ARM: vexpress/dcscb: add CPU use counts to the power up/down API implementation

It is possible for a CPU to be told to power up before it managed
to power itself down.  Solve this race with a usage count to deal
with this possibility as mandated by the MCPM API definition.

Signed-off-by: nicolas Pitre <nico@linaro.org>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Pawel Moll <pawel.moll@arm.com>

diff --git a/arch/arm/mach-vexpress/dcscb.c b/arch/arm/mach-vexpress/dcscb.c
index 2ca4bbce530c59454869288b7ef56118e98879ba..65dee78180822911d773ab66e7f6b32323d78b40 100644 (file)
--- a/arch/arm/mach-vexpress/dcscb.c
+++ b/arch/arm/mach-vexpress/dcscb.c
@@ -44,6 +44,7 @@
 static arch_spinlock_t dcscb_lock = __ARCH_SPIN_LOCK_UNLOCKED;
 
 static void __iomem *dcscb_base;
+static int dcscb_use_count[4][2];
 
 static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
 {
@@ -60,14 +61,27 @@ static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
        local_irq_disable();
        arch_spin_lock(&dcscb_lock);
 
-       rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
-       if (rst_hold & (1 << 8)) {
-               /* remove cluster reset and add individual CPU's reset */
-               rst_hold &= ~(1 << 8);
-               rst_hold |= 0xf;
+       dcscb_use_count[cpu][cluster]++;
+       if (dcscb_use_count[cpu][cluster] == 1) {
+               rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
+               if (rst_hold & (1 << 8)) {
+                       /* remove cluster reset and add individual CPU's reset */
+                       rst_hold &= ~(1 << 8);
+                       rst_hold |= 0xf;
+               }
+               rst_hold &= ~(cpumask | (cpumask << 4));
+               writel_relaxed(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
+       } else if (dcscb_use_count[cpu][cluster] != 2) {
+               /*
+                * The only possible values are:
+                * 0 = CPU down
+                * 1 = CPU (still) up
+                * 2 = CPU requested to be up before it had a chance
+                *     to actually make itself down.
+                * Any other value is a bug.
+                */
+               BUG();
        }
-       rst_hold &= ~(cpumask | (cpumask << 4));
-       writel_relaxed(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
 
        arch_spin_unlock(&dcscb_lock);
        local_irq_enable();
@@ -77,7 +91,8 @@ static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
 
 static void dcscb_power_down(void)
 {
-       unsigned int mpidr, cpu, cluster, rst_hold, cpumask, last_man;
+       unsigned int mpidr, cpu, cluster, rst_hold, cpumask;
+       bool last_man = false, skip_wfi = false;
 
        mpidr = read_cpuid_mpidr();
        cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);
@@ -88,13 +103,26 @@ static void dcscb_power_down(void)
        BUG_ON(cpu >= 4 || cluster >= 2);
 
        arch_spin_lock(&dcscb_lock);
-       rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
-       rst_hold |= cpumask;
-       if (((rst_hold | (rst_hold >> 4)) & 0xf) == 0xf)
-               rst_hold |= (1 << 8);
-       writel_relaxed(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
+       dcscb_use_count[cpu][cluster]--;
+       if (dcscb_use_count[cpu][cluster] == 0) {
+               rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
+               rst_hold |= cpumask;
+               if (((rst_hold | (rst_hold >> 4)) & 0xf) == 0xf) {
+                       rst_hold |= (1 << 8);
+                       last_man = true;
+               }
+               writel_relaxed(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
+       } else if (dcscb_use_count[cpu][cluster] == 1) {
+               /*
+                * A power_up request went ahead of us.
+                * Even if we do not want to shut this CPU down,
+                * the caller expects a certain state as if the WFI
+                * was aborted.  So let's continue with cache cleaning.
+                */
+               skip_wfi = true;
+       } else
+               BUG();
        arch_spin_unlock(&dcscb_lock);
-       last_man = (rst_hold & (1 << 8));
 
        /*
         * Now let's clean our L1 cache and shut ourself down.
@@ -122,7 +150,8 @@ static void dcscb_power_down(void)
 
        /* Now we are prepared for power-down, do it: */
        dsb();
-       wfi();
+       if (!skip_wfi)
+               wfi();
 
        /* Not dead at this point?  Let our caller cope. */
 }
@@ -132,6 +161,19 @@ static const struct mcpm_platform_ops dcscb_power_ops = {
        .power_down     = dcscb_power_down,
 };
 
+static void __init dcscb_usage_count_init(void)
+{
+       unsigned int mpidr, cpu, cluster;
+
+       mpidr = read_cpuid_mpidr();
+       cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+       cluster = MPIDR_AFFINITY_LEVEL(mpidr, 1);
+
+       pr_debug("%s: cpu %u cluster %u\n", __func__, cpu, cluster);
+       BUG_ON(cpu >= 4 || cluster >= 2);
+       dcscb_use_count[cpu][cluster] = 1;
+}
+
 static int __init dcscb_init(void)
 {
        struct device_node *node;
@@ -144,6 +186,8 @@ static int __init dcscb_init(void)
        if (!dcscb_base)
                return -EADDRNOTAVAIL;
 
+       dcscb_usage_count_init();
+
        ret = mcpm_platform_register(&dcscb_power_ops);
        if (ret) {
                iounmap(dcscb_base);