drm/i915/perf: per-gen timebase for checking sample freq

[karo-tx-linux.git] / drivers / gpu / drm / i915 / i915_perf.c

/*
 * Copyright © 2015-2016 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Authors:
 *   Robert Bragg <robert@sixbynine.org>
 */


/**
 * DOC: i915 Perf Overview
 *
 * Gen graphics supports a large number of performance counters that can help
 * driver and application developers understand and optimize their use of the
 * GPU.
 *
 * This i915 perf interface enables userspace to configure and open a file
 * descriptor representing a stream of GPU metrics which can then be read() as
 * a stream of sample records.
 *
 * The interface is particularly suited to exposing buffered metrics that are
 * captured by DMA from the GPU, unsynchronized with and unrelated to the CPU.
 *
 * Streams representing a single context are accessible to applications with a
 * corresponding drm file descriptor, such that OpenGL can use the interface
 * without special privileges. Access to system-wide metrics requires root
 * privileges by default, unless changed via the dev.i915.perf_event_paranoid
 * sysctl option.
 *
 */

/**
 * DOC: i915 Perf History and Comparison with Core Perf
 *
 * The interface was initially inspired by the core Perf infrastructure but
 * some notable differences are:
 *
 * i915 perf file descriptors represent a "stream" instead of an "event"; where
 * a perf event primarily corresponds to a single 64bit value, while a stream
 * might sample sets of tightly-coupled counters, depending on the
 * configuration.  For example the Gen OA unit isn't designed to support
 * orthogonal configurations of individual counters; it's configured for a set
 * of related counters. Samples for an i915 perf stream capturing OA metrics
 * will include a set of counter values packed in a compact HW specific format.
 * The OA unit supports a number of different packing formats which can be
 * selected by the user opening the stream. Perf has support for grouping
 * events, but each event in the group is configured, validated and
 * authenticated individually with separate system calls.
 *
 * i915 perf stream configurations are provided as an array of u64 (key,value)
 * pairs, instead of a fixed struct with multiple miscellaneous config members,
 * interleaved with event-type specific members.
 *
 * i915 perf doesn't support exposing metrics via an mmap'd circular buffer.
 * The supported metrics are being written to memory by the GPU unsynchronized
 * with the CPU, using HW specific packing formats for counter sets. Sometimes
 * the constraints on HW configuration require reports to be filtered before it
 * would be acceptable to expose them to unprivileged applications - to hide
 * the metrics of other processes/contexts. For these use cases a read() based
 * interface is a good fit, and provides an opportunity to filter data as it
 * gets copied from the GPU mapped buffers to userspace buffers.
 *
 *
 * Issues hit with first prototype based on Core Perf
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * The first prototype of this driver was based on the core perf
 * infrastructure, and while we did make that mostly work, with some changes to
 * perf, we found we were breaking or working around too many assumptions baked
 * into perf's currently cpu centric design.
 *
 * In the end we didn't see a clear benefit to making perf's implementation and
 * interface more complex by changing design assumptions while we knew we still
 * wouldn't be able to use any existing perf based userspace tools.
 *
 * Also considering the Gen specific nature of the Observability hardware and
 * how userspace will sometimes need to combine i915 perf OA metrics with
 * side-band OA data captured via MI_REPORT_PERF_COUNT commands; we're
 * expecting the interface to be used by a platform specific userspace such as
 * OpenGL or tools. This is to say; we aren't inherently missing out on having
 * a standard vendor/architecture agnostic interface by not using perf.
 *
 *
 * For posterity, in case we might re-visit trying to adapt core perf to be
 * better suited to exposing i915 metrics these were the main pain points we
 * hit:
 *
 * - The perf based OA PMU driver broke some significant design assumptions:
 *
 *   Existing perf pmus are used for profiling work on a cpu and we were
 *   introducing the idea of _IS_DEVICE pmus with different security
 *   implications, the need to fake cpu-related data (such as user/kernel
 *   registers) to fit with perf's current design, and adding _DEVICE records
 *   as a way to forward device-specific status records.
 *
 *   The OA unit writes reports of counters into a circular buffer, without
 *   involvement from the CPU, making our PMU driver the first of a kind.
 *
 *   Given the way we were periodically forward data from the GPU-mapped, OA
 *   buffer to perf's buffer, those bursts of sample writes looked to perf like
 *   we were sampling too fast and so we had to subvert its throttling checks.
 *
 *   Perf supports groups of counters and allows those to be read via
 *   transactions internally but transactions currently seem designed to be
 *   explicitly initiated from the cpu (say in response to a userspace read())
 *   and while we could pull a report out of the OA buffer we can't
 *   trigger a report from the cpu on demand.
 *
 *   Related to being report based; the OA counters are configured in HW as a
 *   set while perf generally expects counter configurations to be orthogonal.
 *   Although counters can be associated with a group leader as they are
 *   opened, there's no clear precedent for being able to provide group-wide
 *   configuration attributes (for example we want to let userspace choose the
 *   OA unit report format used to capture all counters in a set, or specify a
 *   GPU context to filter metrics on). We avoided using perf's grouping
 *   feature and forwarded OA reports to userspace via perf's 'raw' sample
 *   field. This suited our userspace well considering how coupled the counters
 *   are when dealing with normalizing. It would be inconvenient to split
 *   counters up into separate events, only to require userspace to recombine
 *   them. For Mesa it's also convenient to be forwarded raw, periodic reports
 *   for combining with the side-band raw reports it captures using
 *   MI_REPORT_PERF_COUNT commands.
 *
 *   - As a side note on perf's grouping feature; there was also some concern
 *     that using PERF_FORMAT_GROUP as a way to pack together counter values
 *     would quite drastically inflate our sample sizes, which would likely
 *     lower the effective sampling resolutions we could use when the available
 *     memory bandwidth is limited.
 *
 *     With the OA unit's report formats, counters are packed together as 32
 *     or 40bit values, with the largest report size being 256 bytes.
 *
 *     PERF_FORMAT_GROUP values are 64bit, but there doesn't appear to be a
 *     documented ordering to the values, implying PERF_FORMAT_ID must also be
 *     used to add a 64bit ID before each value; giving 16 bytes per counter.
 *
 *   Related to counter orthogonality; we can't time share the OA unit, while
 *   event scheduling is a central design idea within perf for allowing
 *   userspace to open + enable more events than can be configured in HW at any
 *   one time.  The OA unit is not designed to allow re-configuration while in
 *   use. We can't reconfigure the OA unit without losing internal OA unit
 *   state which we can't access explicitly to save and restore. Reconfiguring
 *   the OA unit is also relatively slow, involving ~100 register writes. From
 *   userspace Mesa also depends on a stable OA configuration when emitting
 *   MI_REPORT_PERF_COUNT commands and importantly the OA unit can't be
 *   disabled while there are outstanding MI_RPC commands lest we hang the
 *   command streamer.
 *
 *   The contents of sample records aren't extensible by device drivers (i.e.
 *   the sample_type bits). As an example; Sourab Gupta had been looking to
 *   attach GPU timestamps to our OA samples. We were shoehorning OA reports
 *   into sample records by using the 'raw' field, but it's tricky to pack more
 *   than one thing into this field because events/core.c currently only lets a
 *   pmu give a single raw data pointer plus len which will be copied into the
 *   ring buffer. To include more than the OA report we'd have to copy the
 *   report into an intermediate larger buffer. I'd been considering allowing a
 *   vector of data+len values to be specified for copying the raw data, but
 *   it felt like a kludge to being using the raw field for this purpose.
 *
 * - It felt like our perf based PMU was making some technical compromises
 *   just for the sake of using perf:
 *
 *   perf_event_open() requires events to either relate to a pid or a specific
 *   cpu core, while our device pmu related to neither.  Events opened with a
 *   pid will be automatically enabled/disabled according to the scheduling of
 *   that process - so not appropriate for us. When an event is related to a
 *   cpu id, perf ensures pmu methods will be invoked via an inter process
 *   interrupt on that core. To avoid invasive changes our userspace opened OA
 *   perf events for a specific cpu. This was workable but it meant the
 *   majority of the OA driver ran in atomic context, including all OA report
 *   forwarding, which wasn't really necessary in our case and seems to make
 *   our locking requirements somewhat complex as we handled the interaction
 *   with the rest of the i915 driver.
 */

#include <linux/anon_inodes.h>
#include <linux/sizes.h>

#include "i915_drv.h"
#include "i915_oa_hsw.h"
#include "i915_oa_bdw.h"
#include "i915_oa_chv.h"
#include "i915_oa_sklgt2.h"
#include "i915_oa_sklgt3.h"
#include "i915_oa_sklgt4.h"
#include "i915_oa_bxt.h"

/* HW requires this to be a power of two, between 128k and 16M, though driver
 * is currently generally designed assuming the largest 16M size is used such
 * that the overflow cases are unlikely in normal operation.
 */
#define OA_BUFFER_SIZE          SZ_16M

#define OA_TAKEN(tail, head)    ((tail - head) & (OA_BUFFER_SIZE - 1))

/**
 * DOC: OA Tail Pointer Race
 *
 * There's a HW race condition between OA unit tail pointer register updates and
 * writes to memory whereby the tail pointer can sometimes get ahead of what's
 * been written out to the OA buffer so far (in terms of what's visible to the
 * CPU).
 *
 * Although this can be observed explicitly while copying reports to userspace
 * by checking for a zeroed report-id field in tail reports, we want to account
 * for this earlier, as part of the oa_buffer_check to avoid lots of redundant
 * read() attempts.
 *
 * In effect we define a tail pointer for reading that lags the real tail
 * pointer by at least %OA_TAIL_MARGIN_NSEC nanoseconds, which gives enough
 * time for the corresponding reports to become visible to the CPU.
 *
 * To manage this we actually track two tail pointers:
 *  1) An 'aging' tail with an associated timestamp that is tracked until we
 *     can trust the corresponding data is visible to the CPU; at which point
 *     it is considered 'aged'.
 *  2) An 'aged' tail that can be used for read()ing.
 *
 * The two separate pointers let us decouple read()s from tail pointer aging.
 *
 * The tail pointers are checked and updated at a limited rate within a hrtimer
 * callback (the same callback that is used for delivering POLLIN events)
 *
 * Initially the tails are marked invalid with %INVALID_TAIL_PTR which
 * indicates that an updated tail pointer is needed.
 *
 * Most of the implementation details for this workaround are in
 * oa_buffer_check_unlocked() and _append_oa_reports()
 *
 * Note for posterity: previously the driver used to define an effective tail
 * pointer that lagged the real pointer by a 'tail margin' measured in bytes
 * derived from %OA_TAIL_MARGIN_NSEC and the configured sampling frequency.
 * This was flawed considering that the OA unit may also automatically generate
 * non-periodic reports (such as on context switch) or the OA unit may be
 * enabled without any periodic sampling.
 */
#define OA_TAIL_MARGIN_NSEC     100000ULL
#define INVALID_TAIL_PTR        0xffffffff

/* frequency for checking whether the OA unit has written new reports to the
 * circular OA buffer...
 */
#define POLL_FREQUENCY 200
#define POLL_PERIOD (NSEC_PER_SEC / POLL_FREQUENCY)

/* for sysctl proc_dointvec_minmax of dev.i915.perf_stream_paranoid */
static int zero;
static int one = 1;
static u32 i915_perf_stream_paranoid = true;

/* The maximum exponent the hardware accepts is 63 (essentially it selects one
 * of the 64bit timestamp bits to trigger reports from) but there's currently
 * no known use case for sampling as infrequently as once per 47 thousand years.
 *
 * Since the timestamps included in OA reports are only 32bits it seems
 * reasonable to limit the OA exponent where it's still possible to account for
 * overflow in OA report timestamps.
 */
#define OA_EXPONENT_MAX 31

#define INVALID_CTX_ID 0xffffffff

/* On Gen8+ automatically triggered OA reports include a 'reason' field... */
#define OAREPORT_REASON_MASK           0x3f
#define OAREPORT_REASON_SHIFT          19
#define OAREPORT_REASON_TIMER          (1<<0)
#define OAREPORT_REASON_CTX_SWITCH     (1<<3)
#define OAREPORT_REASON_CLK_RATIO      (1<<5)


/* For sysctl proc_dointvec_minmax of i915_oa_max_sample_rate
 *
 * The highest sampling frequency we can theoretically program the OA unit
 * with is always half the timestamp frequency: E.g. 6.25Mhz for Haswell.
 *
 * Initialized just before we register the sysctl parameter.
 */
static int oa_sample_rate_hard_limit;

/* Theoretically we can program the OA unit to sample every 160ns but don't
 * allow that by default unless root...
 *
 * The default threshold of 100000Hz is based on perf's similar
 * kernel.perf_event_max_sample_rate sysctl parameter.
 */
static u32 i915_oa_max_sample_rate = 100000;

/* XXX: beware if future OA HW adds new report formats that the current
 * code assumes all reports have a power-of-two size and ~(size - 1) can
 * be used as a mask to align the OA tail pointer.
 */
static struct i915_oa_format hsw_oa_formats[I915_OA_FORMAT_MAX] = {
        [I915_OA_FORMAT_A13]        = { 0, 64 },
        [I915_OA_FORMAT_A29]        = { 1, 128 },
        [I915_OA_FORMAT_A13_B8_C8]  = { 2, 128 },
        /* A29_B8_C8 Disallowed as 192 bytes doesn't factor into buffer size */
        [I915_OA_FORMAT_B4_C8]      = { 4, 64 },
        [I915_OA_FORMAT_A45_B8_C8]  = { 5, 256 },
        [I915_OA_FORMAT_B4_C8_A16]  = { 6, 128 },
        [I915_OA_FORMAT_C4_B8]      = { 7, 64 },
};

static struct i915_oa_format gen8_plus_oa_formats[I915_OA_FORMAT_MAX] = {
        [I915_OA_FORMAT_A12]                = { 0, 64 },
        [I915_OA_FORMAT_A12_B8_C8]          = { 2, 128 },
        [I915_OA_FORMAT_A32u40_A4u32_B8_C8] = { 5, 256 },
        [I915_OA_FORMAT_C4_B8]              = { 7, 64 },
};

#define SAMPLE_OA_REPORT      (1<<0)

/**
 * struct perf_open_properties - for validated properties given to open a stream
 * @sample_flags: `DRM_I915_PERF_PROP_SAMPLE_*` properties are tracked as flags
 * @single_context: Whether a single or all gpu contexts should be monitored
 * @ctx_handle: A gem ctx handle for use with @single_context
 * @metrics_set: An ID for an OA unit metric set advertised via sysfs
 * @oa_format: An OA unit HW report format
 * @oa_periodic: Whether to enable periodic OA unit sampling
 * @oa_period_exponent: The OA unit sampling period is derived from this
 *
 * As read_properties_unlocked() enumerates and validates the properties given
 * to open a stream of metrics the configuration is built up in the structure
 * which starts out zero initialized.
 */
struct perf_open_properties {
        u32 sample_flags;

        u64 single_context:1;
        u64 ctx_handle;

        /* OA sampling state */
        int metrics_set;
        int oa_format;
        bool oa_periodic;
        int oa_period_exponent;
};

static u32 gen8_oa_hw_tail_read(struct drm_i915_private *dev_priv)
{
        return I915_READ(GEN8_OATAILPTR) & GEN8_OATAILPTR_MASK;
}

static u32 gen7_oa_hw_tail_read(struct drm_i915_private *dev_priv)
{
        u32 oastatus1 = I915_READ(GEN7_OASTATUS1);

        return oastatus1 & GEN7_OASTATUS1_TAIL_MASK;
}

/**
 * oa_buffer_check_unlocked - check for data and update tail ptr state
 * @dev_priv: i915 device instance
 *
 * This is either called via fops (for blocking reads in user ctx) or the poll
 * check hrtimer (atomic ctx) to check the OA buffer tail pointer and check
 * if there is data available for userspace to read.
 *
 * This function is central to providing a workaround for the OA unit tail
 * pointer having a race with respect to what data is visible to the CPU.
 * It is responsible for reading tail pointers from the hardware and giving
 * the pointers time to 'age' before they are made available for reading.
 * (See description of OA_TAIL_MARGIN_NSEC above for further details.)
 *
 * Besides returning true when there is data available to read() this function
 * also has the side effect of updating the oa_buffer.tails[], .aging_timestamp
 * and .aged_tail_idx state used for reading.
 *
 * Note: It's safe to read OA config state here unlocked, assuming that this is
 * only called while the stream is enabled, while the global OA configuration
 * can't be modified.
 *
 * Returns: %true if the OA buffer contains data, else %false
 */
static bool oa_buffer_check_unlocked(struct drm_i915_private *dev_priv)
{
        int report_size = dev_priv->perf.oa.oa_buffer.format_size;
        unsigned long flags;
        unsigned int aged_idx;
        u32 head, hw_tail, aged_tail, aging_tail;
        u64 now;

        /* We have to consider the (unlikely) possibility that read() errors
         * could result in an OA buffer reset which might reset the head,
         * tails[] and aged_tail state.
         */
        spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        /* NB: The head we observe here might effectively be a little out of
         * date (between head and tails[aged_idx].offset if there is currently
         * a read() in progress.
         */
        head = dev_priv->perf.oa.oa_buffer.head;

        aged_idx = dev_priv->perf.oa.oa_buffer.aged_tail_idx;
        aged_tail = dev_priv->perf.oa.oa_buffer.tails[aged_idx].offset;
        aging_tail = dev_priv->perf.oa.oa_buffer.tails[!aged_idx].offset;

        hw_tail = dev_priv->perf.oa.ops.oa_hw_tail_read(dev_priv);

        /* The tail pointer increases in 64 byte increments,
         * not in report_size steps...
         */
        hw_tail &= ~(report_size - 1);

        now = ktime_get_mono_fast_ns();

        /* Update the aged tail
         *
         * Flip the tail pointer available for read()s once the aging tail is
         * old enough to trust that the corresponding data will be visible to
         * the CPU...
         *
         * Do this before updating the aging pointer in case we may be able to
         * immediately start aging a new pointer too (if new data has become
         * available) without needing to wait for a later hrtimer callback.
         */
        if (aging_tail != INVALID_TAIL_PTR &&
            ((now - dev_priv->perf.oa.oa_buffer.aging_timestamp) >
             OA_TAIL_MARGIN_NSEC)) {

                aged_idx ^= 1;
                dev_priv->perf.oa.oa_buffer.aged_tail_idx = aged_idx;

                aged_tail = aging_tail;

                /* Mark that we need a new pointer to start aging... */
                dev_priv->perf.oa.oa_buffer.tails[!aged_idx].offset = INVALID_TAIL_PTR;
                aging_tail = INVALID_TAIL_PTR;
        }

        /* Update the aging tail
         *
         * We throttle aging tail updates until we have a new tail that
         * represents >= one report more data than is already available for
         * reading. This ensures there will be enough data for a successful
         * read once this new pointer has aged and ensures we will give the new
         * pointer time to age.
         */
        if (aging_tail == INVALID_TAIL_PTR &&
            (aged_tail == INVALID_TAIL_PTR ||
             OA_TAKEN(hw_tail, aged_tail) >= report_size)) {
                struct i915_vma *vma = dev_priv->perf.oa.oa_buffer.vma;
                u32 gtt_offset = i915_ggtt_offset(vma);

                /* Be paranoid and do a bounds check on the pointer read back
                 * from hardware, just in case some spurious hardware condition
                 * could put the tail out of bounds...
                 */
                if (hw_tail >= gtt_offset &&
                    hw_tail < (gtt_offset + OA_BUFFER_SIZE)) {
                        dev_priv->perf.oa.oa_buffer.tails[!aged_idx].offset =
                                aging_tail = hw_tail;
                        dev_priv->perf.oa.oa_buffer.aging_timestamp = now;
                } else {
                        DRM_ERROR("Ignoring spurious out of range OA buffer tail pointer = %u\n",
                                  hw_tail);
                }
        }

        spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        return aged_tail == INVALID_TAIL_PTR ?
                false : OA_TAKEN(aged_tail, head) >= report_size;
}

/**
 * append_oa_status - Appends a status record to a userspace read() buffer.
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 * @type: The kind of status to report to userspace
 *
 * Writes a status record (such as `DRM_I915_PERF_RECORD_OA_REPORT_LOST`)
 * into the userspace read() buffer.
 *
 * The @buf @offset will only be updated on success.
 *
 * Returns: 0 on success, negative error code on failure.
 */
static int append_oa_status(struct i915_perf_stream *stream,
                            char __user *buf,
                            size_t count,
                            size_t *offset,
                            enum drm_i915_perf_record_type type)
{
        struct drm_i915_perf_record_header header = { type, 0, sizeof(header) };

        if ((count - *offset) < header.size)
                return -ENOSPC;

        if (copy_to_user(buf + *offset, &header, sizeof(header)))
                return -EFAULT;

        (*offset) += header.size;

        return 0;
}

/**
 * append_oa_sample - Copies single OA report into userspace read() buffer.
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 * @report: A single OA report to (optionally) include as part of the sample
 *
 * The contents of a sample are configured through `DRM_I915_PERF_PROP_SAMPLE_*`
 * properties when opening a stream, tracked as `stream->sample_flags`. This
 * function copies the requested components of a single sample to the given
 * read() @buf.
 *
 * The @buf @offset will only be updated on success.
 *
 * Returns: 0 on success, negative error code on failure.
 */
static int append_oa_sample(struct i915_perf_stream *stream,
                            char __user *buf,
                            size_t count,
                            size_t *offset,
                            const u8 *report)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;
        int report_size = dev_priv->perf.oa.oa_buffer.format_size;
        struct drm_i915_perf_record_header header;
        u32 sample_flags = stream->sample_flags;

        header.type = DRM_I915_PERF_RECORD_SAMPLE;
        header.pad = 0;
        header.size = stream->sample_size;

        if ((count - *offset) < header.size)
                return -ENOSPC;

        buf += *offset;
        if (copy_to_user(buf, &header, sizeof(header)))
                return -EFAULT;
        buf += sizeof(header);

        if (sample_flags & SAMPLE_OA_REPORT) {
                if (copy_to_user(buf, report, report_size))
                        return -EFAULT;
        }

        (*offset) += header.size;

        return 0;
}

/**
 * Copies all buffered OA reports into userspace read() buffer.
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 *
 * Notably any error condition resulting in a short read (-%ENOSPC or
 * -%EFAULT) will be returned even though one or more records may
 * have been successfully copied. In this case it's up to the caller
 * to decide if the error should be squashed before returning to
 * userspace.
 *
 * Note: reports are consumed from the head, and appended to the
 * tail, so the tail chases the head?... If you think that's mad
 * and back-to-front you're not alone, but this follows the
 * Gen PRM naming convention.
 *
 * Returns: 0 on success, negative error code on failure.
 */
static int gen8_append_oa_reports(struct i915_perf_stream *stream,
                                  char __user *buf,
                                  size_t count,
                                  size_t *offset)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;
        int report_size = dev_priv->perf.oa.oa_buffer.format_size;
        u8 *oa_buf_base = dev_priv->perf.oa.oa_buffer.vaddr;
        u32 gtt_offset = i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma);
        u32 mask = (OA_BUFFER_SIZE - 1);
        size_t start_offset = *offset;
        unsigned long flags;
        unsigned int aged_tail_idx;
        u32 head, tail;
        u32 taken;
        int ret = 0;

        if (WARN_ON(!stream->enabled))
                return -EIO;

        spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        head = dev_priv->perf.oa.oa_buffer.head;
        aged_tail_idx = dev_priv->perf.oa.oa_buffer.aged_tail_idx;
        tail = dev_priv->perf.oa.oa_buffer.tails[aged_tail_idx].offset;

        spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        /*
         * An invalid tail pointer here means we're still waiting for the poll
         * hrtimer callback to give us a pointer
         */
        if (tail == INVALID_TAIL_PTR)
                return -EAGAIN;

        /*
         * NB: oa_buffer.head/tail include the gtt_offset which we don't want
         * while indexing relative to oa_buf_base.
         */
        head -= gtt_offset;
        tail -= gtt_offset;

        /*
         * An out of bounds or misaligned head or tail pointer implies a driver
         * bug since we validate + align the tail pointers we read from the
         * hardware and we are in full control of the head pointer which should
         * only be incremented by multiples of the report size (notably also
         * all a power of two).
         */
        if (WARN_ONCE(head > OA_BUFFER_SIZE || head % report_size ||
                      tail > OA_BUFFER_SIZE || tail % report_size,
                      "Inconsistent OA buffer pointers: head = %u, tail = %u\n",
                      head, tail))
                return -EIO;


        for (/* none */;
             (taken = OA_TAKEN(tail, head));
             head = (head + report_size) & mask) {
                u8 *report = oa_buf_base + head;
                u32 *report32 = (void *)report;
                u32 ctx_id;
                u32 reason;

                /*
                 * All the report sizes factor neatly into the buffer
                 * size so we never expect to see a report split
                 * between the beginning and end of the buffer.
                 *
                 * Given the initial alignment check a misalignment
                 * here would imply a driver bug that would result
                 * in an overrun.
                 */
                if (WARN_ON((OA_BUFFER_SIZE - head) < report_size)) {
                        DRM_ERROR("Spurious OA head ptr: non-integral report offset\n");
                        break;
                }

                /*
                 * The reason field includes flags identifying what
                 * triggered this specific report (mostly timer
                 * triggered or e.g. due to a context switch).
                 *
                 * This field is never expected to be zero so we can
                 * check that the report isn't invalid before copying
                 * it to userspace...
                 */
                reason = ((report32[0] >> OAREPORT_REASON_SHIFT) &
                          OAREPORT_REASON_MASK);
                if (reason == 0) {
                        if (__ratelimit(&dev_priv->perf.oa.spurious_report_rs))
                                DRM_NOTE("Skipping spurious, invalid OA report\n");
                        continue;
                }

                /*
                 * XXX: Just keep the lower 21 bits for now since I'm not
                 * entirely sure if the HW touches any of the higher bits in
                 * this field
                 */
                ctx_id = report32[2] & 0x1fffff;

                /*
                 * Squash whatever is in the CTX_ID field if it's marked as
                 * invalid to be sure we avoid false-positive, single-context
                 * filtering below...
                 *
                 * Note: that we don't clear the valid_ctx_bit so userspace can
                 * understand that the ID has been squashed by the kernel.
                 */
                if (!(report32[0] & dev_priv->perf.oa.gen8_valid_ctx_bit))
                        ctx_id = report32[2] = INVALID_CTX_ID;

                /*
                 * NB: For Gen 8 the OA unit no longer supports clock gating
                 * off for a specific context and the kernel can't securely
                 * stop the counters from updating as system-wide / global
                 * values.
                 *
                 * Automatic reports now include a context ID so reports can be
                 * filtered on the cpu but it's not worth trying to
                 * automatically subtract/hide counter progress for other
                 * contexts while filtering since we can't stop userspace
                 * issuing MI_REPORT_PERF_COUNT commands which would still
                 * provide a side-band view of the real values.
                 *
                 * To allow userspace (such as Mesa/GL_INTEL_performance_query)
                 * to normalize counters for a single filtered context then it
                 * needs be forwarded bookend context-switch reports so that it
                 * can track switches in between MI_REPORT_PERF_COUNT commands
                 * and can itself subtract/ignore the progress of counters
                 * associated with other contexts. Note that the hardware
                 * automatically triggers reports when switching to a new
                 * context which are tagged with the ID of the newly active
                 * context. To avoid the complexity (and likely fragility) of
                 * reading ahead while parsing reports to try and minimize
                 * forwarding redundant context switch reports (i.e. between
                 * other, unrelated contexts) we simply elect to forward them
                 * all.
                 *
                 * We don't rely solely on the reason field to identify context
                 * switches since it's not-uncommon for periodic samples to
                 * identify a switch before any 'context switch' report.
                 */
                if (!dev_priv->perf.oa.exclusive_stream->ctx ||
                    dev_priv->perf.oa.specific_ctx_id == ctx_id ||
                    (dev_priv->perf.oa.oa_buffer.last_ctx_id ==
                     dev_priv->perf.oa.specific_ctx_id) ||
                    reason & OAREPORT_REASON_CTX_SWITCH) {

                        /*
                         * While filtering for a single context we avoid
                         * leaking the IDs of other contexts.
                         */
                        if (dev_priv->perf.oa.exclusive_stream->ctx &&
                            dev_priv->perf.oa.specific_ctx_id != ctx_id) {
                                report32[2] = INVALID_CTX_ID;
                        }

                        ret = append_oa_sample(stream, buf, count, offset,
                                               report);
                        if (ret)
                                break;

                        dev_priv->perf.oa.oa_buffer.last_ctx_id = ctx_id;
                }

                /*
                 * The above reason field sanity check is based on
                 * the assumption that the OA buffer is initially
                 * zeroed and we reset the field after copying so the
                 * check is still meaningful once old reports start
                 * being overwritten.
                 */
                report32[0] = 0;
        }

        if (start_offset != *offset) {
                spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

                /*
                 * We removed the gtt_offset for the copy loop above, indexing
                 * relative to oa_buf_base so put back here...
                 */
                head += gtt_offset;

                I915_WRITE(GEN8_OAHEADPTR, head & GEN8_OAHEADPTR_MASK);
                dev_priv->perf.oa.oa_buffer.head = head;

                spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);
        }

        return ret;
}

/**
 * gen8_oa_read - copy status records then buffered OA reports
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 *
 * Checks OA unit status registers and if necessary appends corresponding
 * status records for userspace (such as for a buffer full condition) and then
 * initiate appending any buffered OA reports.
 *
 * Updates @offset according to the number of bytes successfully copied into
 * the userspace buffer.
 *
 * NB: some data may be successfully copied to the userspace buffer
 * even if an error is returned, and this is reflected in the
 * updated @offset.
 *
 * Returns: zero on success or a negative error code
 */
static int gen8_oa_read(struct i915_perf_stream *stream,
                        char __user *buf,
                        size_t count,
                        size_t *offset)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;
        u32 oastatus;
        int ret;

        if (WARN_ON(!dev_priv->perf.oa.oa_buffer.vaddr))
                return -EIO;

        oastatus = I915_READ(GEN8_OASTATUS);

        /*
         * We treat OABUFFER_OVERFLOW as a significant error:
         *
         * Although theoretically we could handle this more gracefully
         * sometimes, some Gens don't correctly suppress certain
         * automatically triggered reports in this condition and so we
         * have to assume that old reports are now being trampled
         * over.
         *
         * Considering how we don't currently give userspace control
         * over the OA buffer size and always configure a large 16MB
         * buffer, then a buffer overflow does anyway likely indicate
         * that something has gone quite badly wrong.
         */
        if (oastatus & GEN8_OASTATUS_OABUFFER_OVERFLOW) {
                ret = append_oa_status(stream, buf, count, offset,
                                       DRM_I915_PERF_RECORD_OA_BUFFER_LOST);
                if (ret)
                        return ret;

                DRM_DEBUG("OA buffer overflow (exponent = %d): force restart\n",
                          dev_priv->perf.oa.period_exponent);

                dev_priv->perf.oa.ops.oa_disable(dev_priv);
                dev_priv->perf.oa.ops.oa_enable(dev_priv);

                /*
                 * Note: .oa_enable() is expected to re-init the oabuffer and
                 * reset GEN8_OASTATUS for us
                 */
                oastatus = I915_READ(GEN8_OASTATUS);
        }

        if (oastatus & GEN8_OASTATUS_REPORT_LOST) {
                ret = append_oa_status(stream, buf, count, offset,
                                       DRM_I915_PERF_RECORD_OA_REPORT_LOST);
                if (ret)
                        return ret;
                I915_WRITE(GEN8_OASTATUS,
                           oastatus & ~GEN8_OASTATUS_REPORT_LOST);
        }

        return gen8_append_oa_reports(stream, buf, count, offset);
}

/**
 * Copies all buffered OA reports into userspace read() buffer.
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 *
 * Notably any error condition resulting in a short read (-%ENOSPC or
 * -%EFAULT) will be returned even though one or more records may
 * have been successfully copied. In this case it's up to the caller
 * to decide if the error should be squashed before returning to
 * userspace.
 *
 * Note: reports are consumed from the head, and appended to the
 * tail, so the tail chases the head?... If you think that's mad
 * and back-to-front you're not alone, but this follows the
 * Gen PRM naming convention.
 *
 * Returns: 0 on success, negative error code on failure.
 */
static int gen7_append_oa_reports(struct i915_perf_stream *stream,
                                  char __user *buf,
                                  size_t count,
                                  size_t *offset)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;
        int report_size = dev_priv->perf.oa.oa_buffer.format_size;
        u8 *oa_buf_base = dev_priv->perf.oa.oa_buffer.vaddr;
        u32 gtt_offset = i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma);
        u32 mask = (OA_BUFFER_SIZE - 1);
        size_t start_offset = *offset;
        unsigned long flags;
        unsigned int aged_tail_idx;
        u32 head, tail;
        u32 taken;
        int ret = 0;

        if (WARN_ON(!stream->enabled))
                return -EIO;

        spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        head = dev_priv->perf.oa.oa_buffer.head;
        aged_tail_idx = dev_priv->perf.oa.oa_buffer.aged_tail_idx;
        tail = dev_priv->perf.oa.oa_buffer.tails[aged_tail_idx].offset;

        spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        /* An invalid tail pointer here means we're still waiting for the poll
         * hrtimer callback to give us a pointer
         */
        if (tail == INVALID_TAIL_PTR)
                return -EAGAIN;

        /* NB: oa_buffer.head/tail include the gtt_offset which we don't want
         * while indexing relative to oa_buf_base.
         */
        head -= gtt_offset;
        tail -= gtt_offset;

        /* An out of bounds or misaligned head or tail pointer implies a driver
         * bug since we validate + align the tail pointers we read from the
         * hardware and we are in full control of the head pointer which should
         * only be incremented by multiples of the report size (notably also
         * all a power of two).
         */
        if (WARN_ONCE(head > OA_BUFFER_SIZE || head % report_size ||
                      tail > OA_BUFFER_SIZE || tail % report_size,
                      "Inconsistent OA buffer pointers: head = %u, tail = %u\n",
                      head, tail))
                return -EIO;


        for (/* none */;
             (taken = OA_TAKEN(tail, head));
             head = (head + report_size) & mask) {
                u8 *report = oa_buf_base + head;
                u32 *report32 = (void *)report;

                /* All the report sizes factor neatly into the buffer
                 * size so we never expect to see a report split
                 * between the beginning and end of the buffer.
                 *
                 * Given the initial alignment check a misalignment
                 * here would imply a driver bug that would result
                 * in an overrun.
                 */
                if (WARN_ON((OA_BUFFER_SIZE - head) < report_size)) {
                        DRM_ERROR("Spurious OA head ptr: non-integral report offset\n");
                        break;
                }

                /* The report-ID field for periodic samples includes
                 * some undocumented flags related to what triggered
                 * the report and is never expected to be zero so we
                 * can check that the report isn't invalid before
                 * copying it to userspace...
                 */
                if (report32[0] == 0) {
                        if (__ratelimit(&dev_priv->perf.oa.spurious_report_rs))
                                DRM_NOTE("Skipping spurious, invalid OA report\n");
                        continue;
                }

                ret = append_oa_sample(stream, buf, count, offset, report);
                if (ret)
                        break;

                /* The above report-id field sanity check is based on
                 * the assumption that the OA buffer is initially
                 * zeroed and we reset the field after copying so the
                 * check is still meaningful once old reports start
                 * being overwritten.
                 */
                report32[0] = 0;
        }

        if (start_offset != *offset) {
                spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

                /* We removed the gtt_offset for the copy loop above, indexing
                 * relative to oa_buf_base so put back here...
                 */
                head += gtt_offset;

                I915_WRITE(GEN7_OASTATUS2,
                           ((head & GEN7_OASTATUS2_HEAD_MASK) |
                            OA_MEM_SELECT_GGTT));
                dev_priv->perf.oa.oa_buffer.head = head;

                spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);
        }

        return ret;
}

/**
 * gen7_oa_read - copy status records then buffered OA reports
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 *
 * Checks Gen 7 specific OA unit status registers and if necessary appends
 * corresponding status records for userspace (such as for a buffer full
 * condition) and then initiate appending any buffered OA reports.
 *
 * Updates @offset according to the number of bytes successfully copied into
 * the userspace buffer.
 *
 * Returns: zero on success or a negative error code
 */
static int gen7_oa_read(struct i915_perf_stream *stream,
                        char __user *buf,
                        size_t count,
                        size_t *offset)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;
        u32 oastatus1;
        int ret;

        if (WARN_ON(!dev_priv->perf.oa.oa_buffer.vaddr))
                return -EIO;

        oastatus1 = I915_READ(GEN7_OASTATUS1);

        /* XXX: On Haswell we don't have a safe way to clear oastatus1
         * bits while the OA unit is enabled (while the tail pointer
         * may be updated asynchronously) so we ignore status bits
         * that have already been reported to userspace.
         */
        oastatus1 &= ~dev_priv->perf.oa.gen7_latched_oastatus1;

        /* We treat OABUFFER_OVERFLOW as a significant error:
         *
         * - The status can be interpreted to mean that the buffer is
         *   currently full (with a higher precedence than OA_TAKEN()
         *   which will start to report a near-empty buffer after an
         *   overflow) but it's awkward that we can't clear the status
         *   on Haswell, so without a reset we won't be able to catch
         *   the state again.
         *
         * - Since it also implies the HW has started overwriting old
         *   reports it may also affect our sanity checks for invalid
         *   reports when copying to userspace that assume new reports
         *   are being written to cleared memory.
         *
         * - In the future we may want to introduce a flight recorder
         *   mode where the driver will automatically maintain a safe
         *   guard band between head/tail, avoiding this overflow
         *   condition, but we avoid the added driver complexity for
         *   now.
         */
        if (unlikely(oastatus1 & GEN7_OASTATUS1_OABUFFER_OVERFLOW)) {
                ret = append_oa_status(stream, buf, count, offset,
                                       DRM_I915_PERF_RECORD_OA_BUFFER_LOST);
                if (ret)
                        return ret;

                DRM_DEBUG("OA buffer overflow (exponent = %d): force restart\n",
                          dev_priv->perf.oa.period_exponent);

                dev_priv->perf.oa.ops.oa_disable(dev_priv);
                dev_priv->perf.oa.ops.oa_enable(dev_priv);

                oastatus1 = I915_READ(GEN7_OASTATUS1);
        }

        if (unlikely(oastatus1 & GEN7_OASTATUS1_REPORT_LOST)) {
                ret = append_oa_status(stream, buf, count, offset,
                                       DRM_I915_PERF_RECORD_OA_REPORT_LOST);
                if (ret)
                        return ret;
                dev_priv->perf.oa.gen7_latched_oastatus1 |=
                        GEN7_OASTATUS1_REPORT_LOST;
        }

        return gen7_append_oa_reports(stream, buf, count, offset);
}

/**
 * i915_oa_wait_unlocked - handles blocking IO until OA data available
 * @stream: An i915-perf stream opened for OA metrics
 *
 * Called when userspace tries to read() from a blocking stream FD opened
 * for OA metrics. It waits until the hrtimer callback finds a non-empty
 * OA buffer and wakes us.
 *
 * Note: it's acceptable to have this return with some false positives
 * since any subsequent read handling will return -EAGAIN if there isn't
 * really data ready for userspace yet.
 *
 * Returns: zero on success or a negative error code
 */
static int i915_oa_wait_unlocked(struct i915_perf_stream *stream)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;

        /* We would wait indefinitely if periodic sampling is not enabled */
        if (!dev_priv->perf.oa.periodic)
                return -EIO;

        return wait_event_interruptible(dev_priv->perf.oa.poll_wq,
                                        oa_buffer_check_unlocked(dev_priv));
}

/**
 * i915_oa_poll_wait - call poll_wait() for an OA stream poll()
 * @stream: An i915-perf stream opened for OA metrics
 * @file: An i915 perf stream file
 * @wait: poll() state table
 *
 * For handling userspace polling on an i915 perf stream opened for OA metrics,
 * this starts a poll_wait with the wait queue that our hrtimer callback wakes
 * when it sees data ready to read in the circular OA buffer.
 */
static void i915_oa_poll_wait(struct i915_perf_stream *stream,
                              struct file *file,
                              poll_table *wait)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;

        poll_wait(file, &dev_priv->perf.oa.poll_wq, wait);
}

/**
 * i915_oa_read - just calls through to &i915_oa_ops->read
 * @stream: An i915-perf stream opened for OA metrics
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @offset: (inout): the current position for writing into @buf
 *
 * Updates @offset according to the number of bytes successfully copied into
 * the userspace buffer.
 *
 * Returns: zero on success or a negative error code
 */
static int i915_oa_read(struct i915_perf_stream *stream,
                        char __user *buf,
                        size_t count,
                        size_t *offset)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;

        return dev_priv->perf.oa.ops.read(stream, buf, count, offset);
}

/**
 * oa_get_render_ctx_id - determine and hold ctx hw id
 * @stream: An i915-perf stream opened for OA metrics
 *
 * Determine the render context hw id, and ensure it remains fixed for the
 * lifetime of the stream. This ensures that we don't have to worry about
 * updating the context ID in OACONTROL on the fly.
 *
 * Returns: zero on success or a negative error code
 */
static int oa_get_render_ctx_id(struct i915_perf_stream *stream)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;

        if (i915.enable_execlists)
                dev_priv->perf.oa.specific_ctx_id = stream->ctx->hw_id;
        else {
                struct intel_engine_cs *engine = dev_priv->engine[RCS];
                struct intel_ring *ring;
                int ret;

                ret = i915_mutex_lock_interruptible(&dev_priv->drm);
                if (ret)
                        return ret;

                /*
                 * As the ID is the gtt offset of the context's vma we
                 * pin the vma to ensure the ID remains fixed.
                 *
                 * NB: implied RCS engine...
                 */
                ring = engine->context_pin(engine, stream->ctx);
                mutex_unlock(&dev_priv->drm.struct_mutex);
                if (IS_ERR(ring))
                        return PTR_ERR(ring);


                /*
                 * Explicitly track the ID (instead of calling
                 * i915_ggtt_offset() on the fly) considering the difference
                 * with gen8+ and execlists
                 */
                dev_priv->perf.oa.specific_ctx_id =
                        i915_ggtt_offset(stream->ctx->engine[engine->id].state);
        }

        return 0;
}

/**
 * oa_put_render_ctx_id - counterpart to oa_get_render_ctx_id releases hold
 * @stream: An i915-perf stream opened for OA metrics
 *
 * In case anything needed doing to ensure the context HW ID would remain valid
 * for the lifetime of the stream, then that can be undone here.
 */
static void oa_put_render_ctx_id(struct i915_perf_stream *stream)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;

        if (i915.enable_execlists) {
                dev_priv->perf.oa.specific_ctx_id = INVALID_CTX_ID;
        } else {
                struct intel_engine_cs *engine = dev_priv->engine[RCS];

                mutex_lock(&dev_priv->drm.struct_mutex);

                dev_priv->perf.oa.specific_ctx_id = INVALID_CTX_ID;
                engine->context_unpin(engine, stream->ctx);

                mutex_unlock(&dev_priv->drm.struct_mutex);
        }
}

static void
free_oa_buffer(struct drm_i915_private *i915)
{
        mutex_lock(&i915->drm.struct_mutex);

        i915_gem_object_unpin_map(i915->perf.oa.oa_buffer.vma->obj);
        i915_vma_unpin(i915->perf.oa.oa_buffer.vma);
        i915_gem_object_put(i915->perf.oa.oa_buffer.vma->obj);

        i915->perf.oa.oa_buffer.vma = NULL;
        i915->perf.oa.oa_buffer.vaddr = NULL;

        mutex_unlock(&i915->drm.struct_mutex);
}

static void i915_oa_stream_destroy(struct i915_perf_stream *stream)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;

        BUG_ON(stream != dev_priv->perf.oa.exclusive_stream);

        /*
         * Unset exclusive_stream first, it might be checked while
         * disabling the metric set on gen8+.
         */
        dev_priv->perf.oa.exclusive_stream = NULL;

        dev_priv->perf.oa.ops.disable_metric_set(dev_priv);

        free_oa_buffer(dev_priv);

        intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
        intel_runtime_pm_put(dev_priv);

        if (stream->ctx)
                oa_put_render_ctx_id(stream);

        if (dev_priv->perf.oa.spurious_report_rs.missed) {
                DRM_NOTE("%d spurious OA report notices suppressed due to ratelimiting\n",
                         dev_priv->perf.oa.spurious_report_rs.missed);
        }
}

static void gen7_init_oa_buffer(struct drm_i915_private *dev_priv)
{
        u32 gtt_offset = i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma);
        unsigned long flags;

        spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        /* Pre-DevBDW: OABUFFER must be set with counters off,
         * before OASTATUS1, but after OASTATUS2
         */
        I915_WRITE(GEN7_OASTATUS2, gtt_offset | OA_MEM_SELECT_GGTT); /* head */
        dev_priv->perf.oa.oa_buffer.head = gtt_offset;

        I915_WRITE(GEN7_OABUFFER, gtt_offset);

        I915_WRITE(GEN7_OASTATUS1, gtt_offset | OABUFFER_SIZE_16M); /* tail */

        /* Mark that we need updated tail pointers to read from... */
        dev_priv->perf.oa.oa_buffer.tails[0].offset = INVALID_TAIL_PTR;
        dev_priv->perf.oa.oa_buffer.tails[1].offset = INVALID_TAIL_PTR;

        spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        /* On Haswell we have to track which OASTATUS1 flags we've
         * already seen since they can't be cleared while periodic
         * sampling is enabled.
         */
        dev_priv->perf.oa.gen7_latched_oastatus1 = 0;

        /* NB: although the OA buffer will initially be allocated
         * zeroed via shmfs (and so this memset is redundant when
         * first allocating), we may re-init the OA buffer, either
         * when re-enabling a stream or in error/reset paths.
         *
         * The reason we clear the buffer for each re-init is for the
         * sanity check in gen7_append_oa_reports() that looks at the
         * report-id field to make sure it's non-zero which relies on
         * the assumption that new reports are being written to zeroed
         * memory...
         */
        memset(dev_priv->perf.oa.oa_buffer.vaddr, 0, OA_BUFFER_SIZE);

        /* Maybe make ->pollin per-stream state if we support multiple
         * concurrent streams in the future.
         */
        dev_priv->perf.oa.pollin = false;
}

static void gen8_init_oa_buffer(struct drm_i915_private *dev_priv)
{
        u32 gtt_offset = i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma);
        unsigned long flags;

        spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        I915_WRITE(GEN8_OASTATUS, 0);
        I915_WRITE(GEN8_OAHEADPTR, gtt_offset);
        dev_priv->perf.oa.oa_buffer.head = gtt_offset;

        I915_WRITE(GEN8_OABUFFER_UDW, 0);

        /*
         * PRM says:
         *
         *  "This MMIO must be set before the OATAILPTR
         *  register and after the OAHEADPTR register. This is
         *  to enable proper functionality of the overflow
         *  bit."
         */
        I915_WRITE(GEN8_OABUFFER, gtt_offset |
                   OABUFFER_SIZE_16M | OA_MEM_SELECT_GGTT);
        I915_WRITE(GEN8_OATAILPTR, gtt_offset & GEN8_OATAILPTR_MASK);

        /* Mark that we need updated tail pointers to read from... */
        dev_priv->perf.oa.oa_buffer.tails[0].offset = INVALID_TAIL_PTR;
        dev_priv->perf.oa.oa_buffer.tails[1].offset = INVALID_TAIL_PTR;

        /*
         * Reset state used to recognise context switches, affecting which
         * reports we will forward to userspace while filtering for a single
         * context.
         */
        dev_priv->perf.oa.oa_buffer.last_ctx_id = INVALID_CTX_ID;

        spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);

        /*
         * NB: although the OA buffer will initially be allocated
         * zeroed via shmfs (and so this memset is redundant when
         * first allocating), we may re-init the OA buffer, either
         * when re-enabling a stream or in error/reset paths.
         *
         * The reason we clear the buffer for each re-init is for the
         * sanity check in gen8_append_oa_reports() that looks at the
         * reason field to make sure it's non-zero which relies on
         * the assumption that new reports are being written to zeroed
         * memory...
         */
        memset(dev_priv->perf.oa.oa_buffer.vaddr, 0, OA_BUFFER_SIZE);

        /*
         * Maybe make ->pollin per-stream state if we support multiple
         * concurrent streams in the future.
         */
        dev_priv->perf.oa.pollin = false;
}

static int alloc_oa_buffer(struct drm_i915_private *dev_priv)
{
        struct drm_i915_gem_object *bo;
        struct i915_vma *vma;
        int ret;

        if (WARN_ON(dev_priv->perf.oa.oa_buffer.vma))
                return -ENODEV;

        ret = i915_mutex_lock_interruptible(&dev_priv->drm);
        if (ret)
                return ret;

        BUILD_BUG_ON_NOT_POWER_OF_2(OA_BUFFER_SIZE);
        BUILD_BUG_ON(OA_BUFFER_SIZE < SZ_128K || OA_BUFFER_SIZE > SZ_16M);

        bo = i915_gem_object_create(dev_priv, OA_BUFFER_SIZE);
        if (IS_ERR(bo)) {
                DRM_ERROR("Failed to allocate OA buffer\n");
                ret = PTR_ERR(bo);
                goto unlock;
        }

        ret = i915_gem_object_set_cache_level(bo, I915_CACHE_LLC);
        if (ret)
                goto err_unref;

        /* PreHSW required 512K alignment, HSW requires 16M */
        vma = i915_gem_object_ggtt_pin(bo, NULL, 0, SZ_16M, 0);
        if (IS_ERR(vma)) {
                ret = PTR_ERR(vma);
                goto err_unref;
        }
        dev_priv->perf.oa.oa_buffer.vma = vma;

        dev_priv->perf.oa.oa_buffer.vaddr =
                i915_gem_object_pin_map(bo, I915_MAP_WB);
        if (IS_ERR(dev_priv->perf.oa.oa_buffer.vaddr)) {
                ret = PTR_ERR(dev_priv->perf.oa.oa_buffer.vaddr);
                goto err_unpin;
        }

        dev_priv->perf.oa.ops.init_oa_buffer(dev_priv);

        DRM_DEBUG_DRIVER("OA Buffer initialized, gtt offset = 0x%x, vaddr = %p\n",
                         i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma),
                         dev_priv->perf.oa.oa_buffer.vaddr);

        goto unlock;

err_unpin:
        __i915_vma_unpin(vma);

err_unref:
        i915_gem_object_put(bo);

        dev_priv->perf.oa.oa_buffer.vaddr = NULL;
        dev_priv->perf.oa.oa_buffer.vma = NULL;

unlock:
        mutex_unlock(&dev_priv->drm.struct_mutex);
        return ret;
}

static void config_oa_regs(struct drm_i915_private *dev_priv,
                           const struct i915_oa_reg *regs,
                           int n_regs)
{
        int i;

        for (i = 0; i < n_regs; i++) {
                const struct i915_oa_reg *reg = regs + i;

                I915_WRITE(reg->addr, reg->value);
        }
}

static int hsw_enable_metric_set(struct drm_i915_private *dev_priv)
{
        int ret = i915_oa_select_metric_set_hsw(dev_priv);
        int i;

        if (ret)
                return ret;

        I915_WRITE(GDT_CHICKEN_BITS, (I915_READ(GDT_CHICKEN_BITS) |
                                      GT_NOA_ENABLE));

        /* PRM:
         *
         * OA unit is using “crclk” for its functionality. When trunk
         * level clock gating takes place, OA clock would be gated,
         * unable to count the events from non-render clock domain.
         * Render clock gating must be disabled when OA is enabled to
         * count the events from non-render domain. Unit level clock
         * gating for RCS should also be disabled.
         */
        I915_WRITE(GEN7_MISCCPCTL, (I915_READ(GEN7_MISCCPCTL) &
                                    ~GEN7_DOP_CLOCK_GATE_ENABLE));
        I915_WRITE(GEN6_UCGCTL1, (I915_READ(GEN6_UCGCTL1) |
                                  GEN6_CSUNIT_CLOCK_GATE_DISABLE));

        for (i = 0; i < dev_priv->perf.oa.n_mux_configs; i++) {
                config_oa_regs(dev_priv, dev_priv->perf.oa.mux_regs[i],
                               dev_priv->perf.oa.mux_regs_lens[i]);
        }

        /* It apparently takes a fairly long time for a new MUX
         * configuration to be be applied after these register writes.
         * This delay duration was derived empirically based on the
         * render_basic config but hopefully it covers the maximum
         * configuration latency.
         *
         * As a fallback, the checks in _append_oa_reports() to skip
         * invalid OA reports do also seem to work to discard reports
         * generated before this config has completed - albeit not
         * silently.
         *
         * Unfortunately this is essentially a magic number, since we
         * don't currently know of a reliable mechanism for predicting
         * how long the MUX config will take to apply and besides
         * seeing invalid reports we don't know of a reliable way to
         * explicitly check that the MUX config has landed.
         *
         * It's even possible we've miss characterized the underlying
         * problem - it just seems like the simplest explanation why
         * a delay at this location would mitigate any invalid reports.
         */
        usleep_range(15000, 20000);

        config_oa_regs(dev_priv, dev_priv->perf.oa.b_counter_regs,
                       dev_priv->perf.oa.b_counter_regs_len);

        return 0;
}

static void hsw_disable_metric_set(struct drm_i915_private *dev_priv)
{
        I915_WRITE(GEN6_UCGCTL1, (I915_READ(GEN6_UCGCTL1) &
                                  ~GEN6_CSUNIT_CLOCK_GATE_DISABLE));
        I915_WRITE(GEN7_MISCCPCTL, (I915_READ(GEN7_MISCCPCTL) |
                                    GEN7_DOP_CLOCK_GATE_ENABLE));

        I915_WRITE(GDT_CHICKEN_BITS, (I915_READ(GDT_CHICKEN_BITS) &
                                      ~GT_NOA_ENABLE));
}

/*
 * NB: It must always remain pointer safe to run this even if the OA unit
 * has been disabled.
 *
 * It's fine to put out-of-date values into these per-context registers
 * in the case that the OA unit has been disabled.
 */
static void gen8_update_reg_state_unlocked(struct i915_gem_context *ctx,
                                           u32 *reg_state)
{
        struct drm_i915_private *dev_priv = ctx->i915;
        const struct i915_oa_reg *flex_regs = dev_priv->perf.oa.flex_regs;
        int n_flex_regs = dev_priv->perf.oa.flex_regs_len;
        u32 ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
        u32 ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
        /* The MMIO offsets for Flex EU registers aren't contiguous */
        u32 flex_mmio[] = {
                i915_mmio_reg_offset(EU_PERF_CNTL0),
                i915_mmio_reg_offset(EU_PERF_CNTL1),
                i915_mmio_reg_offset(EU_PERF_CNTL2),
                i915_mmio_reg_offset(EU_PERF_CNTL3),
                i915_mmio_reg_offset(EU_PERF_CNTL4),
                i915_mmio_reg_offset(EU_PERF_CNTL5),
                i915_mmio_reg_offset(EU_PERF_CNTL6),
        };
        int i;

        reg_state[ctx_oactxctrl] = i915_mmio_reg_offset(GEN8_OACTXCONTROL);
        reg_state[ctx_oactxctrl+1] = (dev_priv->perf.oa.period_exponent <<
                                      GEN8_OA_TIMER_PERIOD_SHIFT) |
                                     (dev_priv->perf.oa.periodic ?
                                      GEN8_OA_TIMER_ENABLE : 0) |
                                     GEN8_OA_COUNTER_RESUME;

        for (i = 0; i < ARRAY_SIZE(flex_mmio); i++) {
                u32 state_offset = ctx_flexeu0 + i * 2;
                u32 mmio = flex_mmio[i];

                /*
                 * This arbitrary default will select the 'EU FPU0 Pipeline
                 * Active' event. In the future it's anticipated that there
                 * will be an explicit 'No Event' we can select, but not yet...
                 */
                u32 value = 0;
                int j;

                for (j = 0; j < n_flex_regs; j++) {
                        if (i915_mmio_reg_offset(flex_regs[j].addr) == mmio) {
                                value = flex_regs[j].value;
                                break;
                        }
                }

                reg_state[state_offset] = mmio;
                reg_state[state_offset+1] = value;
        }
}

/*
 * Same as gen8_update_reg_state_unlocked only through the batchbuffer. This
 * is only used by the kernel context.
 */
static int gen8_emit_oa_config(struct drm_i915_gem_request *req)
{
        struct drm_i915_private *dev_priv = req->i915;
        const struct i915_oa_reg *flex_regs = dev_priv->perf.oa.flex_regs;
        int n_flex_regs = dev_priv->perf.oa.flex_regs_len;
        /* The MMIO offsets for Flex EU registers aren't contiguous */
        u32 flex_mmio[] = {
                i915_mmio_reg_offset(EU_PERF_CNTL0),
                i915_mmio_reg_offset(EU_PERF_CNTL1),
                i915_mmio_reg_offset(EU_PERF_CNTL2),
                i915_mmio_reg_offset(EU_PERF_CNTL3),
                i915_mmio_reg_offset(EU_PERF_CNTL4),
                i915_mmio_reg_offset(EU_PERF_CNTL5),
                i915_mmio_reg_offset(EU_PERF_CNTL6),
        };
        u32 *cs;
        int i;

        cs = intel_ring_begin(req, n_flex_regs * 2 + 4);
        if (IS_ERR(cs))
                return PTR_ERR(cs);

        *cs++ = MI_LOAD_REGISTER_IMM(n_flex_regs + 1);

        *cs++ = i915_mmio_reg_offset(GEN8_OACTXCONTROL);
        *cs++ = (dev_priv->perf.oa.period_exponent << GEN8_OA_TIMER_PERIOD_SHIFT) |
                (dev_priv->perf.oa.periodic ? GEN8_OA_TIMER_ENABLE : 0) |
                GEN8_OA_COUNTER_RESUME;

        for (i = 0; i < ARRAY_SIZE(flex_mmio); i++) {
                u32 mmio = flex_mmio[i];

                /*
                 * This arbitrary default will select the 'EU FPU0 Pipeline
                 * Active' event. In the future it's anticipated that there
                 * will be an explicit 'No Event' we can select, but not
                 * yet...
                 */
                u32 value = 0;
                int j;

                for (j = 0; j < n_flex_regs; j++) {
                        if (i915_mmio_reg_offset(flex_regs[j].addr) == mmio) {
                                value = flex_regs[j].value;
                                break;
                        }
                }

                *cs++ = mmio;
                *cs++ = value;
        }

        *cs++ = MI_NOOP;
        intel_ring_advance(req, cs);

        return 0;
}

static int gen8_switch_to_updated_kernel_context(struct drm_i915_private *dev_priv)
{
        struct intel_engine_cs *engine = dev_priv->engine[RCS];
        struct i915_gem_timeline *timeline;
        struct drm_i915_gem_request *req;
        int ret;

        lockdep_assert_held(&dev_priv->drm.struct_mutex);

        i915_gem_retire_requests(dev_priv);

        req = i915_gem_request_alloc(engine, dev_priv->kernel_context);
        if (IS_ERR(req))
                return PTR_ERR(req);

        ret = gen8_emit_oa_config(req);
        if (ret) {
                i915_add_request(req);
                return ret;
        }

        /* Queue this switch after all other activity */
        list_for_each_entry(timeline, &dev_priv->gt.timelines, link) {
                struct drm_i915_gem_request *prev;
                struct intel_timeline *tl;

                tl = &timeline->engine[engine->id];
                prev = i915_gem_active_raw(&tl->last_request,
                                           &dev_priv->drm.struct_mutex);
                if (prev)
                        i915_sw_fence_await_sw_fence_gfp(&req->submit,
                                                         &prev->submit,
                                                         GFP_KERNEL);
        }

        ret = i915_switch_context(req);
        i915_add_request(req);

        return ret;
}

/*
 * Manages updating the per-context aspects of the OA stream
 * configuration across all contexts.
 *
 * The awkward consideration here is that OACTXCONTROL controls the
 * exponent for periodic sampling which is primarily used for system
 * wide profiling where we'd like a consistent sampling period even in
 * the face of context switches.
 *
 * Our approach of updating the register state context (as opposed to
 * say using a workaround batch buffer) ensures that the hardware
 * won't automatically reload an out-of-date timer exponent even
 * transiently before a WA BB could be parsed.
 *
 * This function needs to:
 * - Ensure the currently running context's per-context OA state is
 *   updated
 * - Ensure that all existing contexts will have the correct per-context
 *   OA state if they are scheduled for use.
 * - Ensure any new contexts will be initialized with the correct
 *   per-context OA state.
 *
 * Note: it's only the RCS/Render context that has any OA state.
 */
static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv,
                                       bool interruptible)
{
        struct i915_gem_context *ctx;
        int ret;
        unsigned int wait_flags = I915_WAIT_LOCKED;

        if (interruptible) {
                ret = i915_mutex_lock_interruptible(&dev_priv->drm);
                if (ret)
                        return ret;

                wait_flags |= I915_WAIT_INTERRUPTIBLE;
        } else {
                mutex_lock(&dev_priv->drm.struct_mutex);
        }

        /* Switch away from any user context. */
        ret = gen8_switch_to_updated_kernel_context(dev_priv);
        if (ret)
                goto out;

        /*
         * The OA register config is setup through the context image. This image
         * might be written to by the GPU on context switch (in particular on
         * lite-restore). This means we can't safely update a context's image,
         * if this context is scheduled/submitted to run on the GPU.
         *
         * We could emit the OA register config through the batch buffer but
         * this might leave small interval of time where the OA unit is
         * configured at an invalid sampling period.
         *
         * So far the best way to work around this issue seems to be draining
         * the GPU from any submitted work.
         */
        ret = i915_gem_wait_for_idle(dev_priv, wait_flags);
        if (ret)
                goto out;

        /* Update all contexts now that we've stalled the submission. */
        list_for_each_entry(ctx, &dev_priv->context_list, link) {
                struct intel_context *ce = &ctx->engine[RCS];
                u32 *regs;

                /* OA settings will be set upon first use */
                if (!ce->state)
                        continue;

                regs = i915_gem_object_pin_map(ce->state->obj, I915_MAP_WB);
                if (IS_ERR(regs)) {
                        ret = PTR_ERR(regs);
                        goto out;
                }

                ce->state->obj->mm.dirty = true;
                regs += LRC_STATE_PN * PAGE_SIZE / sizeof(*regs);

                gen8_update_reg_state_unlocked(ctx, regs);

                i915_gem_object_unpin_map(ce->state->obj);
        }

 out:
        mutex_unlock(&dev_priv->drm.struct_mutex);

        return ret;
}

static int gen8_enable_metric_set(struct drm_i915_private *dev_priv)
{
        int ret = dev_priv->perf.oa.ops.select_metric_set(dev_priv);
        int i;

        if (ret)
                return ret;

        /*
         * We disable slice/unslice clock ratio change reports on SKL since
         * they are too noisy. The HW generates a lot of redundant reports
         * where the ratio hasn't really changed causing a lot of redundant
         * work to processes and increasing the chances we'll hit buffer
         * overruns.
         *
         * Although we don't currently use the 'disable overrun' OABUFFER
         * feature it's worth noting that clock ratio reports have to be
         * disabled before considering to use that feature since the HW doesn't
         * correctly block these reports.
         *
         * Currently none of the high-level metrics we have depend on knowing
         * this ratio to normalize.
         *
         * Note: This register is not power context saved and restored, but
         * that's OK considering that we disable RC6 while the OA unit is
         * enabled.
         *
         * The _INCLUDE_CLK_RATIO bit allows the slice/unslice frequency to
         * be read back from automatically triggered reports, as part of the
         * RPT_ID field.
         */
        if (IS_SKYLAKE(dev_priv) || IS_BROXTON(dev_priv)) {
                I915_WRITE(GEN8_OA_DEBUG,
                           _MASKED_BIT_ENABLE(GEN9_OA_DEBUG_DISABLE_CLK_RATIO_REPORTS |
                                              GEN9_OA_DEBUG_INCLUDE_CLK_RATIO));
        }

        /*
         * Update all contexts prior writing the mux configurations as we need
         * to make sure all slices/subslices are ON before writing to NOA
         * registers.
         */
        ret = gen8_configure_all_contexts(dev_priv, true);
        if (ret)
                return ret;

        I915_WRITE(GDT_CHICKEN_BITS, 0xA0);
        for (i = 0; i < dev_priv->perf.oa.n_mux_configs; i++) {
                config_oa_regs(dev_priv, dev_priv->perf.oa.mux_regs[i],
                               dev_priv->perf.oa.mux_regs_lens[i]);
        }
        I915_WRITE(GDT_CHICKEN_BITS, 0x80);

        config_oa_regs(dev_priv, dev_priv->perf.oa.b_counter_regs,
                       dev_priv->perf.oa.b_counter_regs_len);

        return 0;
}

static void gen8_disable_metric_set(struct drm_i915_private *dev_priv)
{
        /* Reset all contexts' slices/subslices configurations. */
        gen8_configure_all_contexts(dev_priv, false);
}

static void gen7_update_oacontrol_locked(struct drm_i915_private *dev_priv)
{
        lockdep_assert_held(&dev_priv->perf.hook_lock);

        if (dev_priv->perf.oa.exclusive_stream->enabled) {
                struct i915_gem_context *ctx =
                        dev_priv->perf.oa.exclusive_stream->ctx;
                u32 ctx_id = dev_priv->perf.oa.specific_ctx_id;

                bool periodic = dev_priv->perf.oa.periodic;
                u32 period_exponent = dev_priv->perf.oa.period_exponent;
                u32 report_format = dev_priv->perf.oa.oa_buffer.format;

                I915_WRITE(GEN7_OACONTROL,
                           (ctx_id & GEN7_OACONTROL_CTX_MASK) |
                           (period_exponent <<
                            GEN7_OACONTROL_TIMER_PERIOD_SHIFT) |
                           (periodic ? GEN7_OACONTROL_TIMER_ENABLE : 0) |
                           (report_format << GEN7_OACONTROL_FORMAT_SHIFT) |
                           (ctx ? GEN7_OACONTROL_PER_CTX_ENABLE : 0) |
                           GEN7_OACONTROL_ENABLE);
        } else
                I915_WRITE(GEN7_OACONTROL, 0);
}

static void gen7_oa_enable(struct drm_i915_private *dev_priv)
{
        unsigned long flags;

        /* Reset buf pointers so we don't forward reports from before now.
         *
         * Think carefully if considering trying to avoid this, since it
         * also ensures status flags and the buffer itself are cleared
         * in error paths, and we have checks for invalid reports based
         * on the assumption that certain fields are written to zeroed
         * memory which this helps maintains.
         */
        gen7_init_oa_buffer(dev_priv);

        spin_lock_irqsave(&dev_priv->perf.hook_lock, flags);
        gen7_update_oacontrol_locked(dev_priv);
        spin_unlock_irqrestore(&dev_priv->perf.hook_lock, flags);
}

static void gen8_oa_enable(struct drm_i915_private *dev_priv)
{
        u32 report_format = dev_priv->perf.oa.oa_buffer.format;

        /*
         * Reset buf pointers so we don't forward reports from before now.
         *
         * Think carefully if considering trying to avoid this, since it
         * also ensures status flags and the buffer itself are cleared
         * in error paths, and we have checks for invalid reports based
         * on the assumption that certain fields are written to zeroed
         * memory which this helps maintains.
         */
        gen8_init_oa_buffer(dev_priv);

        /*
         * Note: we don't rely on the hardware to perform single context
         * filtering and instead filter on the cpu based on the context-id
         * field of reports
         */
        I915_WRITE(GEN8_OACONTROL, (report_format <<
                                    GEN8_OA_REPORT_FORMAT_SHIFT) |
                                   GEN8_OA_COUNTER_ENABLE);
}

/**
 * i915_oa_stream_enable - handle `I915_PERF_IOCTL_ENABLE` for OA stream
 * @stream: An i915 perf stream opened for OA metrics
 *
 * [Re]enables hardware periodic sampling according to the period configured
 * when opening the stream. This also starts a hrtimer that will periodically
 * check for data in the circular OA buffer for notifying userspace (e.g.
 * during a read() or poll()).
 */
static void i915_oa_stream_enable(struct i915_perf_stream *stream)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;

        dev_priv->perf.oa.ops.oa_enable(dev_priv);

        if (dev_priv->perf.oa.periodic)
                hrtimer_start(&dev_priv->perf.oa.poll_check_timer,
                              ns_to_ktime(POLL_PERIOD),
                              HRTIMER_MODE_REL_PINNED);
}

static void gen7_oa_disable(struct drm_i915_private *dev_priv)
{
        I915_WRITE(GEN7_OACONTROL, 0);
}

static void gen8_oa_disable(struct drm_i915_private *dev_priv)
{
        I915_WRITE(GEN8_OACONTROL, 0);
}

/**
 * i915_oa_stream_disable - handle `I915_PERF_IOCTL_DISABLE` for OA stream
 * @stream: An i915 perf stream opened for OA metrics
 *
 * Stops the OA unit from periodically writing counter reports into the
 * circular OA buffer. This also stops the hrtimer that periodically checks for
 * data in the circular OA buffer, for notifying userspace.
 */
static void i915_oa_stream_disable(struct i915_perf_stream *stream)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;

        dev_priv->perf.oa.ops.oa_disable(dev_priv);

        if (dev_priv->perf.oa.periodic)
                hrtimer_cancel(&dev_priv->perf.oa.poll_check_timer);
}

static const struct i915_perf_stream_ops i915_oa_stream_ops = {
        .destroy = i915_oa_stream_destroy,
        .enable = i915_oa_stream_enable,
        .disable = i915_oa_stream_disable,
        .wait_unlocked = i915_oa_wait_unlocked,
        .poll_wait = i915_oa_poll_wait,
        .read = i915_oa_read,
};

/**
 * i915_oa_stream_init - validate combined props for OA stream and init
 * @stream: An i915 perf stream
 * @param: The open parameters passed to `DRM_I915_PERF_OPEN`
 * @props: The property state that configures stream (individually validated)
 *
 * While read_properties_unlocked() validates properties in isolation it
 * doesn't ensure that the combination necessarily makes sense.
 *
 * At this point it has been determined that userspace wants a stream of
 * OA metrics, but still we need to further validate the combined
 * properties are OK.
 *
 * If the configuration makes sense then we can allocate memory for
 * a circular OA buffer and apply the requested metric set configuration.
 *
 * Returns: zero on success or a negative error code.
 */
static int i915_oa_stream_init(struct i915_perf_stream *stream,
                               struct drm_i915_perf_open_param *param,
                               struct perf_open_properties *props)
{
        struct drm_i915_private *dev_priv = stream->dev_priv;
        int format_size;
        int ret;

        /* If the sysfs metrics/ directory wasn't registered for some
         * reason then don't let userspace try their luck with config
         * IDs
         */
        if (!dev_priv->perf.metrics_kobj) {
                DRM_DEBUG("OA metrics weren't advertised via sysfs\n");
                return -EINVAL;
        }

        if (!(props->sample_flags & SAMPLE_OA_REPORT)) {
                DRM_DEBUG("Only OA report sampling supported\n");
                return -EINVAL;
        }

        if (!dev_priv->perf.oa.ops.init_oa_buffer) {
                DRM_DEBUG("OA unit not supported\n");
                return -ENODEV;
        }

        /* To avoid the complexity of having to accurately filter
         * counter reports and marshal to the appropriate client
         * we currently only allow exclusive access
         */
        if (dev_priv->perf.oa.exclusive_stream) {
                DRM_DEBUG("OA unit already in use\n");
                return -EBUSY;
        }

        if (!props->metrics_set) {
                DRM_DEBUG("OA metric set not specified\n");
                return -EINVAL;
        }

        if (!props->oa_format) {
                DRM_DEBUG("OA report format not specified\n");
                return -EINVAL;
        }

        /* We set up some ratelimit state to potentially throttle any _NOTES
         * about spurious, invalid OA reports which we don't forward to
         * userspace.
         *
         * The initialization is associated with opening the stream (not driver
         * init) considering we print a _NOTE about any throttling when closing
         * the stream instead of waiting until driver _fini which no one would
         * ever see.
         *
         * Using the same limiting factors as printk_ratelimit()
         */
        ratelimit_state_init(&dev_priv->perf.oa.spurious_report_rs,
                             5 * HZ, 10);
        /* Since we use a DRM_NOTE for spurious reports it would be
         * inconsistent to let __ratelimit() automatically print a warning for
         * throttling.
         */
        ratelimit_set_flags(&dev_priv->perf.oa.spurious_report_rs,
                            RATELIMIT_MSG_ON_RELEASE);

        stream->sample_size = sizeof(struct drm_i915_perf_record_header);

        format_size = dev_priv->perf.oa.oa_formats[props->oa_format].size;

        stream->sample_flags |= SAMPLE_OA_REPORT;
        stream->sample_size += format_size;

        dev_priv->perf.oa.oa_buffer.format_size = format_size;
        if (WARN_ON(dev_priv->perf.oa.oa_buffer.format_size == 0))
                return -EINVAL;

        dev_priv->perf.oa.oa_buffer.format =
                dev_priv->perf.oa.oa_formats[props->oa_format].format;

        dev_priv->perf.oa.metrics_set = props->metrics_set;

        dev_priv->perf.oa.periodic = props->oa_periodic;
        if (dev_priv->perf.oa.periodic)
                dev_priv->perf.oa.period_exponent = props->oa_period_exponent;

        if (stream->ctx) {
                ret = oa_get_render_ctx_id(stream);
                if (ret)
                        return ret;
        }

        ret = alloc_oa_buffer(dev_priv);
        if (ret)
                goto err_oa_buf_alloc;

        /* PRM - observability performance counters:
         *
         *   OACONTROL, performance counter enable, note:
         *
         *   "When this bit is set, in order to have coherent counts,
         *   RC6 power state and trunk clock gating must be disabled.
         *   This can be achieved by programming MMIO registers as
         *   0xA094=0 and 0xA090[31]=1"
         *
         *   In our case we are expecting that taking pm + FORCEWAKE
         *   references will effectively disable RC6.
         */
        intel_runtime_pm_get(dev_priv);
        intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);

        ret = dev_priv->perf.oa.ops.enable_metric_set(dev_priv);
        if (ret)
                goto err_enable;

        stream->ops = &i915_oa_stream_ops;

        dev_priv->perf.oa.exclusive_stream = stream;

        return 0;

err_enable:
        intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
        intel_runtime_pm_put(dev_priv);
        free_oa_buffer(dev_priv);

err_oa_buf_alloc:
        if (stream->ctx)
                oa_put_render_ctx_id(stream);

        return ret;
}

void i915_oa_init_reg_state(struct intel_engine_cs *engine,
                            struct i915_gem_context *ctx,
                            u32 *reg_state)
{
        struct drm_i915_private *dev_priv = engine->i915;

        if (engine->id != RCS)
                return;

        if (!dev_priv->perf.initialized)
                return;

        gen8_update_reg_state_unlocked(ctx, reg_state);
}

/**
 * i915_perf_read_locked - &i915_perf_stream_ops->read with error normalisation
 * @stream: An i915 perf stream
 * @file: An i915 perf stream file
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @ppos: (inout) file seek position (unused)
 *
 * Besides wrapping &i915_perf_stream_ops->read this provides a common place to
 * ensure that if we've successfully copied any data then reporting that takes
 * precedence over any internal error status, so the data isn't lost.
 *
 * For example ret will be -ENOSPC whenever there is more buffered data than
 * can be copied to userspace, but that's only interesting if we weren't able
 * to copy some data because it implies the userspace buffer is too small to
 * receive a single record (and we never split records).
 *
 * Another case with ret == -EFAULT is more of a grey area since it would seem
 * like bad form for userspace to ask us to overrun its buffer, but the user
 * knows best:
 *
 *   http://yarchive.net/comp/linux/partial_reads_writes.html
 *
 * Returns: The number of bytes copied or a negative error code on failure.
 */
static ssize_t i915_perf_read_locked(struct i915_perf_stream *stream,
                                     struct file *file,
                                     char __user *buf,
                                     size_t count,
                                     loff_t *ppos)
{
        /* Note we keep the offset (aka bytes read) separate from any
         * error status so that the final check for whether we return
         * the bytes read with a higher precedence than any error (see
         * comment below) doesn't need to be handled/duplicated in
         * stream->ops->read() implementations.
         */
        size_t offset = 0;
        int ret = stream->ops->read(stream, buf, count, &offset);

        return offset ?: (ret ?: -EAGAIN);
}

/**
 * i915_perf_read - handles read() FOP for i915 perf stream FDs
 * @file: An i915 perf stream file
 * @buf: destination buffer given by userspace
 * @count: the number of bytes userspace wants to read
 * @ppos: (inout) file seek position (unused)
 *
 * The entry point for handling a read() on a stream file descriptor from
 * userspace. Most of the work is left to the i915_perf_read_locked() and
 * &i915_perf_stream_ops->read but to save having stream implementations (of
 * which we might have multiple later) we handle blocking read here.
 *
 * We can also consistently treat trying to read from a disabled stream
 * as an IO error so implementations can assume the stream is enabled
 * while reading.
 *
 * Returns: The number of bytes copied or a negative error code on failure.
 */
static ssize_t i915_perf_read(struct file *file,
                              char __user *buf,
                              size_t count,
                              loff_t *ppos)
{
        struct i915_perf_stream *stream = file->private_data;
        struct drm_i915_private *dev_priv = stream->dev_priv;
        ssize_t ret;

        /* To ensure it's handled consistently we simply treat all reads of a
         * disabled stream as an error. In particular it might otherwise lead
         * to a deadlock for blocking file descriptors...
         */
        if (!stream->enabled)
                return -EIO;

        if (!(file->f_flags & O_NONBLOCK)) {
                /* There's the small chance of false positives from
                 * stream->ops->wait_unlocked.
                 *
                 * E.g. with single context filtering since we only wait until
                 * oabuffer has >= 1 report we don't immediately know whether
                 * any reports really belong to the current context
                 */
                do {
                        ret = stream->ops->wait_unlocked(stream);
                        if (ret)
                                return ret;

                        mutex_lock(&dev_priv->perf.lock);
                        ret = i915_perf_read_locked(stream, file,
                                                    buf, count, ppos);
                        mutex_unlock(&dev_priv->perf.lock);
                } while (ret == -EAGAIN);
        } else {
                mutex_lock(&dev_priv->perf.lock);
                ret = i915_perf_read_locked(stream, file, buf, count, ppos);
                mutex_unlock(&dev_priv->perf.lock);
        }

        /* We allow the poll checking to sometimes report false positive POLLIN
         * events where we might actually report EAGAIN on read() if there's
         * not really any data available. In this situation though we don't
         * want to enter a busy loop between poll() reporting a POLLIN event
         * and read() returning -EAGAIN. Clearing the oa.pollin state here
         * effectively ensures we back off until the next hrtimer callback
         * before reporting another POLLIN event.
         */
        if (ret >= 0 || ret == -EAGAIN) {
                /* Maybe make ->pollin per-stream state if we support multiple
                 * concurrent streams in the future.
                 */
                dev_priv->perf.oa.pollin = false;
        }

        return ret;
}

static enum hrtimer_restart oa_poll_check_timer_cb(struct hrtimer *hrtimer)
{
        struct drm_i915_private *dev_priv =
                container_of(hrtimer, typeof(*dev_priv),
                             perf.oa.poll_check_timer);

        if (oa_buffer_check_unlocked(dev_priv)) {
                dev_priv->perf.oa.pollin = true;
                wake_up(&dev_priv->perf.oa.poll_wq);
        }

        hrtimer_forward_now(hrtimer, ns_to_ktime(POLL_PERIOD));

        return HRTIMER_RESTART;
}

/**
 * i915_perf_poll_locked - poll_wait() with a suitable wait queue for stream
 * @dev_priv: i915 device instance
 * @stream: An i915 perf stream
 * @file: An i915 perf stream file
 * @wait: poll() state table
 *
 * For handling userspace polling on an i915 perf stream, this calls through to
 * &i915_perf_stream_ops->poll_wait to call poll_wait() with a wait queue that
 * will be woken for new stream data.
 *
 * Note: The &drm_i915_private->perf.lock mutex has been taken to serialize
 * with any non-file-operation driver hooks.
 *
 * Returns: any poll events that are ready without sleeping
 */
static unsigned int i915_perf_poll_locked(struct drm_i915_private *dev_priv,
                                          struct i915_perf_stream *stream,
                                          struct file *file,
                                          poll_table *wait)
{
        unsigned int events = 0;

        stream->ops->poll_wait(stream, file, wait);

        /* Note: we don't explicitly check whether there's something to read
         * here since this path may be very hot depending on what else
         * userspace is polling, or on the timeout in use. We rely solely on
         * the hrtimer/oa_poll_check_timer_cb to notify us when there are
         * samples to read.
         */
        if (dev_priv->perf.oa.pollin)
                events |= POLLIN;

        return events;
}

/**
 * i915_perf_poll - call poll_wait() with a suitable wait queue for stream
 * @file: An i915 perf stream file
 * @wait: poll() state table
 *
 * For handling userspace polling on an i915 perf stream, this ensures
 * poll_wait() gets called with a wait queue that will be woken for new stream
 * data.
 *
 * Note: Implementation deferred to i915_perf_poll_locked()
 *
 * Returns: any poll events that are ready without sleeping
 */
static unsigned int i915_perf_poll(struct file *file, poll_table *wait)
{
        struct i915_perf_stream *stream = file->private_data;
        struct drm_i915_private *dev_priv = stream->dev_priv;
        int ret;

        mutex_lock(&dev_priv->perf.lock);
        ret = i915_perf_poll_locked(dev_priv, stream, file, wait);
        mutex_unlock(&dev_priv->perf.lock);

        return ret;
}

/**
 * i915_perf_enable_locked - handle `I915_PERF_IOCTL_ENABLE` ioctl
 * @stream: A disabled i915 perf stream
 *
 * [Re]enables the associated capture of data for this stream.
 *
 * If a stream was previously enabled then there's currently no intention
 * to provide userspace any guarantee about the preservation of previously
 * buffered data.
 */
static void i915_perf_enable_locked(struct i915_perf_stream *stream)
{
        if (stream->enabled)
                return;

        /* Allow stream->ops->enable() to refer to this */
        stream->enabled = true;

        if (stream->ops->enable)
                stream->ops->enable(stream);
}

/**
 * i915_perf_disable_locked - handle `I915_PERF_IOCTL_DISABLE` ioctl
 * @stream: An enabled i915 perf stream
 *
 * Disables the associated capture of data for this stream.
 *
 * The intention is that disabling an re-enabling a stream will ideally be
 * cheaper than destroying and re-opening a stream with the same configuration,
 * though there are no formal guarantees about what state or buffered data
 * must be retained between disabling and re-enabling a stream.
 *
 * Note: while a stream is disabled it's considered an error for userspace
 * to attempt to read from the stream (-EIO).
 */
static void i915_perf_disable_locked(struct i915_perf_stream *stream)
{
        if (!stream->enabled)
                return;

        /* Allow stream->ops->disable() to refer to this */
        stream->enabled = false;

        if (stream->ops->disable)
                stream->ops->disable(stream);
}

/**
 * i915_perf_ioctl - support ioctl() usage with i915 perf stream FDs
 * @stream: An i915 perf stream
 * @cmd: the ioctl request
 * @arg: the ioctl data
 *
 * Note: The &drm_i915_private->perf.lock mutex has been taken to serialize
 * with any non-file-operation driver hooks.
 *
 * Returns: zero on success or a negative error code. Returns -EINVAL for
 * an unknown ioctl request.
 */
static long i915_perf_ioctl_locked(struct i915_perf_stream *stream,
                                   unsigned int cmd,
                                   unsigned long arg)
{
        switch (cmd) {
        case I915_PERF_IOCTL_ENABLE:
                i915_perf_enable_locked(stream);
                return 0;
        case I915_PERF_IOCTL_DISABLE:
                i915_perf_disable_locked(stream);
                return 0;
        }

        return -EINVAL;
}

/**
 * i915_perf_ioctl - support ioctl() usage with i915 perf stream FDs
 * @file: An i915 perf stream file
 * @cmd: the ioctl request
 * @arg: the ioctl data
 *
 * Implementation deferred to i915_perf_ioctl_locked().
 *
 * Returns: zero on success or a negative error code. Returns -EINVAL for
 * an unknown ioctl request.
 */
static long i915_perf_ioctl(struct file *file,
                            unsigned int cmd,
                            unsigned long arg)
{
        struct i915_perf_stream *stream = file->private_data;
        struct drm_i915_private *dev_priv = stream->dev_priv;
        long ret;

        mutex_lock(&dev_priv->perf.lock);
        ret = i915_perf_ioctl_locked(stream, cmd, arg);
        mutex_unlock(&dev_priv->perf.lock);

        return ret;
}

/**
 * i915_perf_destroy_locked - destroy an i915 perf stream
 * @stream: An i915 perf stream
 *
 * Frees all resources associated with the given i915 perf @stream, disabling
 * any associated data capture in the process.
 *
 * Note: The &drm_i915_private->perf.lock mutex has been taken to serialize
 * with any non-file-operation driver hooks.
 */
static void i915_perf_destroy_locked(struct i915_perf_stream *stream)
{
        if (stream->enabled)
                i915_perf_disable_locked(stream);

        if (stream->ops->destroy)
                stream->ops->destroy(stream);

        list_del(&stream->link);

        if (stream->ctx)
                i915_gem_context_put_unlocked(stream->ctx);

        kfree(stream);
}

/**
 * i915_perf_release - handles userspace close() of a stream file
 * @inode: anonymous inode associated with file
 * @file: An i915 perf stream file
 *
 * Cleans up any resources associated with an open i915 perf stream file.
 *
 * NB: close() can't really fail from the userspace point of view.
 *
 * Returns: zero on success or a negative error code.
 */
static int i915_perf_release(struct inode *inode, struct file *file)
{
        struct i915_perf_stream *stream = file->private_data;
        struct drm_i915_private *dev_priv = stream->dev_priv;

        mutex_lock(&dev_priv->perf.lock);
        i915_perf_destroy_locked(stream);
        mutex_unlock(&dev_priv->perf.lock);

        return 0;
}


static const struct file_operations fops = {
        .owner          = THIS_MODULE,
        .llseek         = no_llseek,
        .release        = i915_perf_release,
        .poll           = i915_perf_poll,
        .read           = i915_perf_read,
        .unlocked_ioctl = i915_perf_ioctl,
};


static struct i915_gem_context *
lookup_context(struct drm_i915_private *dev_priv,
               struct drm_i915_file_private *file_priv,
               u32 ctx_user_handle)
{
        struct i915_gem_context *ctx;
        int ret;

        ret = i915_mutex_lock_interruptible(&dev_priv->drm);
        if (ret)
                return ERR_PTR(ret);

        ctx = i915_gem_context_lookup(file_priv, ctx_user_handle);
        if (!IS_ERR(ctx))
                i915_gem_context_get(ctx);

        mutex_unlock(&dev_priv->drm.struct_mutex);

        return ctx;
}

/**
 * i915_perf_open_ioctl_locked - DRM ioctl() for userspace to open a stream FD
 * @dev_priv: i915 device instance
 * @param: The open parameters passed to 'DRM_I915_PERF_OPEN`
 * @props: individually validated u64 property value pairs
 * @file: drm file
 *
 * See i915_perf_ioctl_open() for interface details.
 *
 * Implements further stream config validation and stream initialization on
 * behalf of i915_perf_open_ioctl() with the &drm_i915_private->perf.lock mutex
 * taken to serialize with any non-file-operation driver hooks.
 *
 * Note: at this point the @props have only been validated in isolation and
 * it's still necessary to validate that the combination of properties makes
 * sense.
 *
 * In the case where userspace is interested in OA unit metrics then further
 * config validation and stream initialization details will be handled by
 * i915_oa_stream_init(). The code here should only validate config state that
 * will be relevant to all stream types / backends.
 *
 * Returns: zero on success or a negative error code.
 */
static int
i915_perf_open_ioctl_locked(struct drm_i915_private *dev_priv,
                            struct drm_i915_perf_open_param *param,
                            struct perf_open_properties *props,
                            struct drm_file *file)
{
        struct i915_gem_context *specific_ctx = NULL;
        struct i915_perf_stream *stream = NULL;
        unsigned long f_flags = 0;
        bool privileged_op = true;
        int stream_fd;
        int ret;

        if (props->single_context) {
                u32 ctx_handle = props->ctx_handle;
                struct drm_i915_file_private *file_priv = file->driver_priv;

                specific_ctx = lookup_context(dev_priv, file_priv, ctx_handle);
                if (IS_ERR(specific_ctx)) {
                        ret = PTR_ERR(specific_ctx);
                        if (ret != -EINTR)
                                DRM_DEBUG("Failed to look up context with ID %u for opening perf stream\n",
                                          ctx_handle);
                        goto err;
                }
        }

        /*
         * On Haswell the OA unit supports clock gating off for a specific
         * context and in this mode there's no visibility of metrics for the
         * rest of the system, which we consider acceptable for a
         * non-privileged client.
         *
         * For Gen8+ the OA unit no longer supports clock gating off for a
         * specific context and the kernel can't securely stop the counters
         * from updating as system-wide / global values. Even though we can
         * filter reports based on the included context ID we can't block
         * clients from seeing the raw / global counter values via
         * MI_REPORT_PERF_COUNT commands and so consider it a privileged op to
         * enable the OA unit by default.
         */
        if (IS_HASWELL(dev_priv) && specific_ctx)
                privileged_op = false;

        /* Similar to perf's kernel.perf_paranoid_cpu sysctl option
         * we check a dev.i915.perf_stream_paranoid sysctl option
         * to determine if it's ok to access system wide OA counters
         * without CAP_SYS_ADMIN privileges.
         */
        if (privileged_op &&
            i915_perf_stream_paranoid && !capable(CAP_SYS_ADMIN)) {
                DRM_DEBUG("Insufficient privileges to open system-wide i915 perf stream\n");
                ret = -EACCES;
                goto err_ctx;
        }

        stream = kzalloc(sizeof(*stream), GFP_KERNEL);
        if (!stream) {
                ret = -ENOMEM;
                goto err_ctx;
        }

        stream->dev_priv = dev_priv;
        stream->ctx = specific_ctx;

        ret = i915_oa_stream_init(stream, param, props);
        if (ret)
                goto err_alloc;

        /* we avoid simply assigning stream->sample_flags = props->sample_flags
         * to have _stream_init check the combination of sample flags more
         * thoroughly, but still this is the expected result at this point.
         */
        if (WARN_ON(stream->sample_flags != props->sample_flags)) {
                ret = -ENODEV;
                goto err_flags;
        }

        list_add(&stream->link, &dev_priv->perf.streams);

        if (param->flags & I915_PERF_FLAG_FD_CLOEXEC)
                f_flags |= O_CLOEXEC;
        if (param->flags & I915_PERF_FLAG_FD_NONBLOCK)
                f_flags |= O_NONBLOCK;

        stream_fd = anon_inode_getfd("[i915_perf]", &fops, stream, f_flags);
        if (stream_fd < 0) {
                ret = stream_fd;
                goto err_open;
        }

        if (!(param->flags & I915_PERF_FLAG_DISABLED))
                i915_perf_enable_locked(stream);

        return stream_fd;

err_open:
        list_del(&stream->link);
err_flags:
        if (stream->ops->destroy)
                stream->ops->destroy(stream);
err_alloc:
        kfree(stream);
err_ctx:
        if (specific_ctx)
                i915_gem_context_put_unlocked(specific_ctx);
err:
        return ret;
}

static u64 oa_exponent_to_ns(struct drm_i915_private *dev_priv, int exponent)
{
        return div_u64(1000000000ULL * (2ULL << exponent),
                       dev_priv->perf.oa.timestamp_frequency);
}

/**
 * read_properties_unlocked - validate + copy userspace stream open properties
 * @dev_priv: i915 device instance
 * @uprops: The array of u64 key value pairs given by userspace
 * @n_props: The number of key value pairs expected in @uprops
 * @props: The stream configuration built up while validating properties
 *
 * Note this function only validates properties in isolation it doesn't
 * validate that the combination of properties makes sense or that all
 * properties necessary for a particular kind of stream have been set.
 *
 * Note that there currently aren't any ordering requirements for properties so
 * we shouldn't validate or assume anything about ordering here. This doesn't
 * rule out defining new properties with ordering requirements in the future.
 */
static int read_properties_unlocked(struct drm_i915_private *dev_priv,
                                    u64 __user *uprops,
                                    u32 n_props,
                                    struct perf_open_properties *props)
{
        u64 __user *uprop = uprops;
        int i;

        memset(props, 0, sizeof(struct perf_open_properties));

        if (!n_props) {
                DRM_DEBUG("No i915 perf properties given\n");
                return -EINVAL;
        }

        /* Considering that ID = 0 is reserved and assuming that we don't
         * (currently) expect any configurations to ever specify duplicate
         * values for a particular property ID then the last _PROP_MAX value is
         * one greater than the maximum number of properties we expect to get
         * from userspace.
         */
        if (n_props >= DRM_I915_PERF_PROP_MAX) {
                DRM_DEBUG("More i915 perf properties specified than exist\n");
                return -EINVAL;
        }

        for (i = 0; i < n_props; i++) {
                u64 oa_period, oa_freq_hz;
                u64 id, value;
                int ret;

                ret = get_user(id, uprop);
                if (ret)
                        return ret;

                ret = get_user(value, uprop + 1);
                if (ret)
                        return ret;

                if (id == 0 || id >= DRM_I915_PERF_PROP_MAX) {
                        DRM_DEBUG("Unknown i915 perf property ID\n");
                        return -EINVAL;
                }

                switch ((enum drm_i915_perf_property_id)id) {
                case DRM_I915_PERF_PROP_CTX_HANDLE:
                        props->single_context = 1;
                        props->ctx_handle = value;
                        break;
                case DRM_I915_PERF_PROP_SAMPLE_OA:
                        props->sample_flags |= SAMPLE_OA_REPORT;
                        break;
                case DRM_I915_PERF_PROP_OA_METRICS_SET:
                        if (value == 0 ||
                            value > dev_priv->perf.oa.n_builtin_sets) {
                                DRM_DEBUG("Unknown OA metric set ID\n");
                                return -EINVAL;
                        }
                        props->metrics_set = value;
                        break;
                case DRM_I915_PERF_PROP_OA_FORMAT:
                        if (value == 0 || value >= I915_OA_FORMAT_MAX) {
                                DRM_DEBUG("Out-of-range OA report format %llu\n",
                                          value);
                                return -EINVAL;
                        }
                        if (!dev_priv->perf.oa.oa_formats[value].size) {
                                DRM_DEBUG("Unsupported OA report format %llu\n",
                                          value);
                                return -EINVAL;
                        }
                        props->oa_format = value;
                        break;
                case DRM_I915_PERF_PROP_OA_EXPONENT:
                        if (value > OA_EXPONENT_MAX) {
                                DRM_DEBUG("OA timer exponent too high (> %u)\n",
                                         OA_EXPONENT_MAX);
                                return -EINVAL;
                        }

                        /* Theoretically we can program the OA unit to sample
                         * e.g. every 160ns for HSW, 167ns for BDW/SKL or 104ns
                         * for BXT. We don't allow such high sampling
                         * frequencies by default unless root.
                         */

                        BUILD_BUG_ON(sizeof(oa_period) != 8);
                        oa_period = oa_exponent_to_ns(dev_priv, value);

                        /* This check is primarily to ensure that oa_period <=
                         * UINT32_MAX (before passing to do_div which only
                         * accepts a u32 denominator), but we can also skip
                         * checking anything < 1Hz which implicitly can't be
                         * limited via an integer oa_max_sample_rate.
                         */
                        if (oa_period <= NSEC_PER_SEC) {
                                u64 tmp = NSEC_PER_SEC;
                                do_div(tmp, oa_period);
                                oa_freq_hz = tmp;
                        } else
                                oa_freq_hz = 0;

                        if (oa_freq_hz > i915_oa_max_sample_rate &&
                            !capable(CAP_SYS_ADMIN)) {
                                DRM_DEBUG("OA exponent would exceed the max sampling frequency (sysctl dev.i915.oa_max_sample_rate) %uHz without root privileges\n",
                                          i915_oa_max_sample_rate);
                                return -EACCES;
                        }

                        props->oa_periodic = true;
                        props->oa_period_exponent = value;
                        break;
                case DRM_I915_PERF_PROP_MAX:
                        MISSING_CASE(id);
                        return -EINVAL;
                }

                uprop += 2;
        }

        return 0;
}

/**
 * i915_perf_open_ioctl - DRM ioctl() for userspace to open a stream FD
 * @dev: drm device
 * @data: ioctl data copied from userspace (unvalidated)
 * @file: drm file
 *
 * Validates the stream open parameters given by userspace including flags
 * and an array of u64 key, value pair properties.
 *
 * Very little is assumed up front about the nature of the stream being
 * opened (for instance we don't assume it's for periodic OA unit metrics). An
 * i915-perf stream is expected to be a suitable interface for other forms of
 * buffered data written by the GPU besides periodic OA metrics.
 *
 * Note we copy the properties from userspace outside of the i915 perf
 * mutex to avoid an awkward lockdep with mmap_sem.
 *
 * Most of the implementation details are handled by
 * i915_perf_open_ioctl_locked() after taking the &drm_i915_private->perf.lock
 * mutex for serializing with any non-file-operation driver hooks.
 *
 * Return: A newly opened i915 Perf stream file descriptor or negative
 * error code on failure.
 */
int i915_perf_open_ioctl(struct drm_device *dev, void *data,
                         struct drm_file *file)
{
        struct drm_i915_private *dev_priv = dev->dev_private;
        struct drm_i915_perf_open_param *param = data;
        struct perf_open_properties props;
        u32 known_open_flags;
        int ret;

        if (!dev_priv->perf.initialized) {
                DRM_DEBUG("i915 perf interface not available for this system\n");
                return -ENOTSUPP;
        }

        known_open_flags = I915_PERF_FLAG_FD_CLOEXEC |
                           I915_PERF_FLAG_FD_NONBLOCK |
                           I915_PERF_FLAG_DISABLED;
        if (param->flags & ~known_open_flags) {
                DRM_DEBUG("Unknown drm_i915_perf_open_param flag\n");
                return -EINVAL;
        }

        ret = read_properties_unlocked(dev_priv,
                                       u64_to_user_ptr(param->properties_ptr),
                                       param->num_properties,
                                       &props);
        if (ret)
                return ret;

        mutex_lock(&dev_priv->perf.lock);
        ret = i915_perf_open_ioctl_locked(dev_priv, param, &props, file);
        mutex_unlock(&dev_priv->perf.lock);

        return ret;
}

/**
 * i915_perf_register - exposes i915-perf to userspace
 * @dev_priv: i915 device instance
 *
 * In particular OA metric sets are advertised under a sysfs metrics/
 * directory allowing userspace to enumerate valid IDs that can be
 * used to open an i915-perf stream.
 */
void i915_perf_register(struct drm_i915_private *dev_priv)
{
        if (!dev_priv->perf.initialized)
                return;

        /* To be sure we're synchronized with an attempted
         * i915_perf_open_ioctl(); considering that we register after
         * being exposed to userspace.
         */
        mutex_lock(&dev_priv->perf.lock);

        dev_priv->perf.metrics_kobj =
                kobject_create_and_add("metrics",
                                       &dev_priv->drm.primary->kdev->kobj);
        if (!dev_priv->perf.metrics_kobj)
                goto exit;

        if (IS_HASWELL(dev_priv)) {
                if (i915_perf_register_sysfs_hsw(dev_priv))
                        goto sysfs_error;
        } else if (IS_BROADWELL(dev_priv)) {
                if (i915_perf_register_sysfs_bdw(dev_priv))
                        goto sysfs_error;
        } else if (IS_CHERRYVIEW(dev_priv)) {
                if (i915_perf_register_sysfs_chv(dev_priv))
                        goto sysfs_error;
        } else if (IS_SKYLAKE(dev_priv)) {
                if (IS_SKL_GT2(dev_priv)) {
                        if (i915_perf_register_sysfs_sklgt2(dev_priv))
                                goto sysfs_error;
                } else if (IS_SKL_GT3(dev_priv)) {
                        if (i915_perf_register_sysfs_sklgt3(dev_priv))
                                goto sysfs_error;
                } else if (IS_SKL_GT4(dev_priv)) {
                        if (i915_perf_register_sysfs_sklgt4(dev_priv))
                                goto sysfs_error;
                } else
                        goto sysfs_error;
        } else if (IS_BROXTON(dev_priv)) {
                if (i915_perf_register_sysfs_bxt(dev_priv))
                        goto sysfs_error;
        }

        goto exit;

sysfs_error:
        kobject_put(dev_priv->perf.metrics_kobj);
        dev_priv->perf.metrics_kobj = NULL;

exit:
        mutex_unlock(&dev_priv->perf.lock);
}

/**
 * i915_perf_unregister - hide i915-perf from userspace
 * @dev_priv: i915 device instance
 *
 * i915-perf state cleanup is split up into an 'unregister' and
 * 'deinit' phase where the interface is first hidden from
 * userspace by i915_perf_unregister() before cleaning up
 * remaining state in i915_perf_fini().
 */
void i915_perf_unregister(struct drm_i915_private *dev_priv)
{
        if (!dev_priv->perf.metrics_kobj)
                return;

        if (IS_HASWELL(dev_priv))
                i915_perf_unregister_sysfs_hsw(dev_priv);
        else if (IS_BROADWELL(dev_priv))
                i915_perf_unregister_sysfs_bdw(dev_priv);
        else if (IS_CHERRYVIEW(dev_priv))
                i915_perf_unregister_sysfs_chv(dev_priv);
        else if (IS_SKYLAKE(dev_priv)) {
                if (IS_SKL_GT2(dev_priv))
                        i915_perf_unregister_sysfs_sklgt2(dev_priv);
                else if (IS_SKL_GT3(dev_priv))
                        i915_perf_unregister_sysfs_sklgt3(dev_priv);
                else if (IS_SKL_GT4(dev_priv))
                        i915_perf_unregister_sysfs_sklgt4(dev_priv);
        } else if (IS_BROXTON(dev_priv))
                i915_perf_unregister_sysfs_bxt(dev_priv);

        kobject_put(dev_priv->perf.metrics_kobj);
        dev_priv->perf.metrics_kobj = NULL;
}

static struct ctl_table oa_table[] = {
        {
         .procname = "perf_stream_paranoid",
         .data = &i915_perf_stream_paranoid,
         .maxlen = sizeof(i915_perf_stream_paranoid),
         .mode = 0644,
         .proc_handler = proc_dointvec_minmax,
         .extra1 = &zero,
         .extra2 = &one,
         },
        {
         .procname = "oa_max_sample_rate",
         .data = &i915_oa_max_sample_rate,
         .maxlen = sizeof(i915_oa_max_sample_rate),
         .mode = 0644,
         .proc_handler = proc_dointvec_minmax,
         .extra1 = &zero,
         .extra2 = &oa_sample_rate_hard_limit,
         },
        {}
};

static struct ctl_table i915_root[] = {
        {
         .procname = "i915",
         .maxlen = 0,
         .mode = 0555,
         .child = oa_table,
         },
        {}
};

static struct ctl_table dev_root[] = {
        {
         .procname = "dev",
         .maxlen = 0,
         .mode = 0555,
         .child = i915_root,
         },
        {}
};

/**
 * i915_perf_init - initialize i915-perf state on module load
 * @dev_priv: i915 device instance
 *
 * Initializes i915-perf state without exposing anything to userspace.
 *
 * Note: i915-perf initialization is split into an 'init' and 'register'
 * phase with the i915_perf_register() exposing state to userspace.
 */
void i915_perf_init(struct drm_i915_private *dev_priv)
{
        dev_priv->perf.oa.n_builtin_sets = 0;

        if (IS_HASWELL(dev_priv)) {
                dev_priv->perf.oa.ops.init_oa_buffer = gen7_init_oa_buffer;
                dev_priv->perf.oa.ops.enable_metric_set = hsw_enable_metric_set;
                dev_priv->perf.oa.ops.disable_metric_set = hsw_disable_metric_set;
                dev_priv->perf.oa.ops.oa_enable = gen7_oa_enable;
                dev_priv->perf.oa.ops.oa_disable = gen7_oa_disable;
                dev_priv->perf.oa.ops.read = gen7_oa_read;
                dev_priv->perf.oa.ops.oa_hw_tail_read =
                        gen7_oa_hw_tail_read;

                dev_priv->perf.oa.timestamp_frequency = 12500000;

                dev_priv->perf.oa.oa_formats = hsw_oa_formats;

                dev_priv->perf.oa.n_builtin_sets =
                        i915_oa_n_builtin_metric_sets_hsw;
        } else if (i915.enable_execlists) {
                /* Note: that although we could theoretically also support the
                 * legacy ringbuffer mode on BDW (and earlier iterations of
                 * this driver, before upstreaming did this) it didn't seem
                 * worth the complexity to maintain now that BDW+ enable
                 * execlist mode by default.
                 */

                if (IS_GEN8(dev_priv)) {
                        dev_priv->perf.oa.ctx_oactxctrl_offset = 0x120;
                        dev_priv->perf.oa.ctx_flexeu0_offset = 0x2ce;

                        dev_priv->perf.oa.timestamp_frequency = 12500000;

                        dev_priv->perf.oa.gen8_valid_ctx_bit = (1<<25);

                        if (IS_BROADWELL(dev_priv)) {
                                dev_priv->perf.oa.n_builtin_sets =
                                        i915_oa_n_builtin_metric_sets_bdw;
                                dev_priv->perf.oa.ops.select_metric_set =
                                        i915_oa_select_metric_set_bdw;
                        } else if (IS_CHERRYVIEW(dev_priv)) {
                                dev_priv->perf.oa.n_builtin_sets =
                                        i915_oa_n_builtin_metric_sets_chv;
                                dev_priv->perf.oa.ops.select_metric_set =
                                        i915_oa_select_metric_set_chv;
                        }
                } else if (IS_GEN9(dev_priv)) {
                        dev_priv->perf.oa.ctx_oactxctrl_offset = 0x128;
                        dev_priv->perf.oa.ctx_flexeu0_offset = 0x3de;

                        dev_priv->perf.oa.timestamp_frequency = 12000000;

                        dev_priv->perf.oa.gen8_valid_ctx_bit = (1<<16);

                        if (IS_SKL_GT2(dev_priv)) {
                                dev_priv->perf.oa.n_builtin_sets =
                                        i915_oa_n_builtin_metric_sets_sklgt2;
                                dev_priv->perf.oa.ops.select_metric_set =
                                        i915_oa_select_metric_set_sklgt2;
                        } else if (IS_SKL_GT3(dev_priv)) {
                                dev_priv->perf.oa.n_builtin_sets =
                                        i915_oa_n_builtin_metric_sets_sklgt3;
                                dev_priv->perf.oa.ops.select_metric_set =
                                        i915_oa_select_metric_set_sklgt3;
                        } else if (IS_SKL_GT4(dev_priv)) {
                                dev_priv->perf.oa.n_builtin_sets =
                                        i915_oa_n_builtin_metric_sets_sklgt4;
                                dev_priv->perf.oa.ops.select_metric_set =
                                        i915_oa_select_metric_set_sklgt4;
                        } else if (IS_BROXTON(dev_priv)) {
                                dev_priv->perf.oa.timestamp_frequency = 19200000;

                                dev_priv->perf.oa.n_builtin_sets =
                                        i915_oa_n_builtin_metric_sets_bxt;
                                dev_priv->perf.oa.ops.select_metric_set =
                                        i915_oa_select_metric_set_bxt;
                        }
                }

                if (dev_priv->perf.oa.n_builtin_sets) {
                        dev_priv->perf.oa.ops.init_oa_buffer = gen8_init_oa_buffer;
                        dev_priv->perf.oa.ops.enable_metric_set =
                                gen8_enable_metric_set;
                        dev_priv->perf.oa.ops.disable_metric_set =
                                gen8_disable_metric_set;
                        dev_priv->perf.oa.ops.oa_enable = gen8_oa_enable;
                        dev_priv->perf.oa.ops.oa_disable = gen8_oa_disable;
                        dev_priv->perf.oa.ops.read = gen8_oa_read;
                        dev_priv->perf.oa.ops.oa_hw_tail_read =
                                gen8_oa_hw_tail_read;

                        dev_priv->perf.oa.oa_formats = gen8_plus_oa_formats;
                }
        }

        if (dev_priv->perf.oa.n_builtin_sets) {
                hrtimer_init(&dev_priv->perf.oa.poll_check_timer,
                                CLOCK_MONOTONIC, HRTIMER_MODE_REL);
                dev_priv->perf.oa.poll_check_timer.function = oa_poll_check_timer_cb;
                init_waitqueue_head(&dev_priv->perf.oa.poll_wq);

                INIT_LIST_HEAD(&dev_priv->perf.streams);
                mutex_init(&dev_priv->perf.lock);
                spin_lock_init(&dev_priv->perf.hook_lock);
                spin_lock_init(&dev_priv->perf.oa.oa_buffer.ptr_lock);

                oa_sample_rate_hard_limit =
                        dev_priv->perf.oa.timestamp_frequency / 2;
                dev_priv->perf.sysctl_header = register_sysctl_table(dev_root);

                dev_priv->perf.initialized = true;
        }
}

/**
 * i915_perf_fini - Counter part to i915_perf_init()
 * @dev_priv: i915 device instance
 */
void i915_perf_fini(struct drm_i915_private *dev_priv)
{
        if (!dev_priv->perf.initialized)
                return;

        unregister_sysctl_table(dev_priv->perf.sysctl_header);

        memset(&dev_priv->perf.oa.ops, 0, sizeof(dev_priv->perf.oa.ops));

        dev_priv->perf.initialized = false;
}