drivers/hwtracing/stm/core.c

   1 /*
   2  * System Trace Module (STM) infrastructure
   3  * Copyright (c) 2014, Intel Corporation.
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms and conditions of the GNU General Public License,
   7  * version 2, as published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  12  * more details.
  13  *
  14  * STM class implements generic infrastructure for  System Trace Module devices
  15  * as defined in MIPI STPv2 specification.
  16  */
  17
  18 #include <linux/uaccess.h>
  19 #include <linux/kernel.h>
  20 #include <linux/module.h>
  21 #include <linux/device.h>
  22 #include <linux/compat.h>
  23 #include <linux/kdev_t.h>
  24 #include <linux/srcu.h>
  25 #include <linux/slab.h>
  26 #include <linux/stm.h>
  27 #include <linux/fs.h>
  28 #include <linux/mm.h>
  29 #include "stm.h"
  30
  31 #include <uapi/linux/stm.h>
  32
  33 static unsigned int stm_core_up;
  34
  35 /*
  36  * The SRCU here makes sure that STM device doesn't disappear from under a
  37  * stm_source_write() caller, which may want to have as little overhead as
  38  * possible.
  39  */
  40 static struct srcu_struct stm_source_srcu;
  41
  42 static ssize_t masters_show(struct device *dev,
  43                             struct device_attribute *attr,
  44                             char *buf)
  45 {
  46         struct stm_device *stm = to_stm_device(dev);
  47         int ret;
  48
  49         ret = sprintf(buf, "%u %u\n", stm->data->sw_start, stm->data->sw_end);
  50
  51         return ret;
  52 }
  53
  54 static DEVICE_ATTR_RO(masters);
  55
  56 static ssize_t channels_show(struct device *dev,
  57                              struct device_attribute *attr,
  58                              char *buf)
  59 {
  60         struct stm_device *stm = to_stm_device(dev);
  61         int ret;
  62
  63         ret = sprintf(buf, "%u\n", stm->data->sw_nchannels);
  64
  65         return ret;
  66 }
  67
  68 static DEVICE_ATTR_RO(channels);
  69
  70 static struct attribute *stm_attrs[] = {
  71         &dev_attr_masters.attr,
  72         &dev_attr_channels.attr,
  73         NULL,
  74 };
  75
  76 ATTRIBUTE_GROUPS(stm);
  77
  78 static struct class stm_class = {
  79         .name           = "stm",
  80         .dev_groups     = stm_groups,
  81 };
  82
  83 static int stm_dev_match(struct device *dev, const void *data)
  84 {
  85         const char *name = data;
  86
  87         return sysfs_streq(name, dev_name(dev));
  88 }
  89
  90 /**
  91  * stm_find_device() - find stm device by name
  92  * @buf:        character buffer containing the name
  93  *
  94  * This is called when either policy gets assigned to an stm device or an
  95  * stm_source device gets linked to an stm device.
  96  *
  97  * This grabs device's reference (get_device()) and module reference, both
  98  * of which the calling path needs to make sure to drop with stm_put_device().
  99  *
 100  * Return:      stm device pointer or null if lookup failed.
 101  */
 102 struct stm_device *stm_find_device(const char *buf)
 103 {
 104         struct stm_device *stm;
 105         struct device *dev;
 106
 107         if (!stm_core_up)
 108                 return NULL;
 109
 110         dev = class_find_device(&stm_class, NULL, buf, stm_dev_match);
 111         if (!dev)
 112                 return NULL;
 113
 114         stm = to_stm_device(dev);
 115         if (!try_module_get(stm->owner)) {
 116                 put_device(dev);
 117                 return NULL;
 118         }
 119
 120         return stm;
 121 }
 122
 123 /**
 124  * stm_put_device() - drop references on the stm device
 125  * @stm:        stm device, previously acquired by stm_find_device()
 126  *
 127  * This drops the module reference and device reference taken by
 128  * stm_find_device().
 129  */
 130 void stm_put_device(struct stm_device *stm)
 131 {
 132         module_put(stm->owner);
 133         put_device(&stm->dev);
 134 }
 135
 136 /*
 137  * Internally we only care about software-writable masters here, that is the
 138  * ones in the range [stm_data->sw_start..stm_data..sw_end], however we need
 139  * original master numbers to be visible externally, since they are the ones
 140  * that will appear in the STP stream. Thus, the internal bookkeeping uses
 141  * $master - stm_data->sw_start to reference master descriptors and such.
 142  */
 143
 144 #define __stm_master(_s, _m)                            \
 145         ((_s)->masters[(_m) - (_s)->data->sw_start])
 146
 147 static inline struct stp_master *
 148 stm_master(struct stm_device *stm, unsigned int idx)
 149 {
 150         if (idx < stm->data->sw_start || idx > stm->data->sw_end)
 151                 return NULL;
 152
 153         return __stm_master(stm, idx);
 154 }
 155
 156 static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
 157 {
 158         struct stp_master *master;
 159         size_t size;
 160
 161         size = ALIGN(stm->data->sw_nchannels, 8) / 8;
 162         size += sizeof(struct stp_master);
 163         master = kzalloc(size, GFP_ATOMIC);
 164         if (!master)
 165                 return -ENOMEM;
 166
 167         master->nr_free = stm->data->sw_nchannels;
 168         __stm_master(stm, idx) = master;
 169
 170         return 0;
 171 }
 172
 173 static void stp_master_free(struct stm_device *stm, unsigned int idx)
 174 {
 175         struct stp_master *master = stm_master(stm, idx);
 176
 177         if (!master)
 178                 return;
 179
 180         __stm_master(stm, idx) = NULL;
 181         kfree(master);
 182 }
 183
 184 static void stm_output_claim(struct stm_device *stm, struct stm_output *output)
 185 {
 186         struct stp_master *master = stm_master(stm, output->master);
 187
 188         if (WARN_ON_ONCE(master->nr_free < output->nr_chans))
 189                 return;
 190
 191         bitmap_allocate_region(&master->chan_map[0], output->channel,
 192                                ilog2(output->nr_chans));
 193
 194         master->nr_free -= output->nr_chans;
 195 }
 196
 197 static void
 198 stm_output_disclaim(struct stm_device *stm, struct stm_output *output)
 199 {
 200         struct stp_master *master = stm_master(stm, output->master);
 201
 202         bitmap_release_region(&master->chan_map[0], output->channel,
 203                               ilog2(output->nr_chans));
 204
 205         output->nr_chans = 0;
 206         master->nr_free += output->nr_chans;
 207 }
 208
 209 /*
 210  * This is like bitmap_find_free_region(), except it can ignore @start bits
 211  * at the beginning.
 212  */
 213 static int find_free_channels(unsigned long *bitmap, unsigned int start,
 214                               unsigned int end, unsigned int width)
 215 {
 216         unsigned int pos;
 217         int i;
 218
 219         for (pos = start; pos < end + 1; pos = ALIGN(pos, width)) {
 220                 pos = find_next_zero_bit(bitmap, end + 1, pos);
 221                 if (pos + width > end + 1)
 222                         break;
 223
 224                 if (pos & (width - 1))
 225                         continue;
 226
 227                 for (i = 1; i < width && !test_bit(pos + i, bitmap); i++)
 228                         ;
 229                 if (i == width)
 230                         return pos;
 231         }
 232
 233         return -1;
 234 }
 235
 236 static unsigned int
 237 stm_find_master_chan(struct stm_device *stm, unsigned int width,
 238                      unsigned int *mstart, unsigned int mend,
 239                      unsigned int *cstart, unsigned int cend)
 240 {
 241         struct stp_master *master;
 242         unsigned int midx;
 243         int pos, err;
 244
 245         for (midx = *mstart; midx <= mend; midx++) {
 246                 if (!stm_master(stm, midx)) {
 247                         err = stp_master_alloc(stm, midx);
 248                         if (err)
 249                                 return err;
 250                 }
 251
 252                 master = stm_master(stm, midx);
 253
 254                 if (!master->nr_free)
 255                         continue;
 256
 257                 pos = find_free_channels(master->chan_map, *cstart, cend,
 258                                          width);
 259                 if (pos < 0)
 260                         continue;
 261
 262                 *mstart = midx;
 263                 *cstart = pos;
 264                 return 0;
 265         }
 266
 267         return -ENOSPC;
 268 }
 269
 270 static int stm_output_assign(struct stm_device *stm, unsigned int width,
 271                              struct stp_policy_node *policy_node,
 272                              struct stm_output *output)
 273 {
 274         unsigned int midx, cidx, mend, cend;
 275         int ret = -EINVAL;
 276
 277         if (width > stm->data->sw_nchannels)
 278                 return -EINVAL;
 279
 280         if (policy_node) {
 281                 stp_policy_node_get_ranges(policy_node,
 282                                            &midx, &mend, &cidx, &cend);
 283         } else {
 284                 midx = stm->data->sw_start;
 285                 cidx = 0;
 286                 mend = stm->data->sw_end;
 287                 cend = stm->data->sw_nchannels - 1;
 288         }
 289
 290         spin_lock(&stm->mc_lock);
 291         /* output is already assigned -- shouldn't happen */
 292         if (WARN_ON_ONCE(output->nr_chans))
 293                 goto unlock;
 294
 295         ret = stm_find_master_chan(stm, width, &midx, mend, &cidx, cend);
 296         if (ret)
 297                 goto unlock;
 298
 299         output->master = midx;
 300         output->channel = cidx;
 301         output->nr_chans = width;
 302         stm_output_claim(stm, output);
 303         dev_dbg(&stm->dev, "assigned %u:%u (+%u)\n", midx, cidx, width);
 304
 305         ret = 0;
 306 unlock:
 307         spin_unlock(&stm->mc_lock);
 308
 309         return ret;
 310 }
 311
 312 static void stm_output_free(struct stm_device *stm, struct stm_output *output)
 313 {
 314         spin_lock(&stm->mc_lock);
 315         if (output->nr_chans)
 316                 stm_output_disclaim(stm, output);
 317         spin_unlock(&stm->mc_lock);
 318 }
 319
 320 static int major_match(struct device *dev, const void *data)
 321 {
 322         unsigned int major = *(unsigned int *)data;
 323
 324         return MAJOR(dev->devt) == major;
 325 }
 326
 327 static int stm_char_open(struct inode *inode, struct file *file)
 328 {
 329         struct stm_file *stmf;
 330         struct device *dev;
 331         unsigned int major = imajor(inode);
 332         int err = -ENODEV;
 333
 334         dev = class_find_device(&stm_class, NULL, &major, major_match);
 335         if (!dev)
 336                 return -ENODEV;
 337
 338         stmf = kzalloc(sizeof(*stmf), GFP_KERNEL);
 339         if (!stmf)
 340                 return -ENOMEM;
 341
 342         stmf->stm = to_stm_device(dev);
 343
 344         if (!try_module_get(stmf->stm->owner))
 345                 goto err_free;
 346
 347         file->private_data = stmf;
 348
 349         return nonseekable_open(inode, file);
 350
 351 err_free:
 352         kfree(stmf);
 353
 354         return err;
 355 }
 356
 357 static int stm_char_release(struct inode *inode, struct file *file)
 358 {
 359         struct stm_file *stmf = file->private_data;
 360
 361         stm_output_free(stmf->stm, &stmf->output);
 362         stm_put_device(stmf->stm);
 363         kfree(stmf);
 364
 365         return 0;
 366 }
 367
 368 static int stm_file_assign(struct stm_file *stmf, char *id, unsigned int width)
 369 {
 370         struct stm_device *stm = stmf->stm;
 371         int ret;
 372
 373         stmf->policy_node = stp_policy_node_lookup(stm, id);
 374
 375         ret = stm_output_assign(stm, width, stmf->policy_node, &stmf->output);
 376
 377         if (stmf->policy_node)
 378                 stp_policy_node_put(stmf->policy_node);
 379
 380         return ret;
 381 }
 382
 383 static void stm_write(struct stm_data *data, unsigned int master,
 384                       unsigned int channel, const char *buf, size_t count)
 385 {
 386         unsigned int flags = STP_PACKET_TIMESTAMPED;
 387         const unsigned char *p = buf, nil = 0;
 388         size_t pos;
 389         ssize_t sz;
 390
 391         for (pos = 0, p = buf; count > pos; pos += sz, p += sz) {
 392                 sz = min_t(unsigned int, count - pos, 8);
 393                 sz = data->packet(data, master, channel, STP_PACKET_DATA, flags,
 394                                   sz, p);
 395                 flags = 0;
 396         }
 397
 398         data->packet(data, master, channel, STP_PACKET_FLAG, 0, 0, &nil);
 399 }
 400
 401 static ssize_t stm_char_write(struct file *file, const char __user *buf,
 402                               size_t count, loff_t *ppos)
 403 {
 404         struct stm_file *stmf = file->private_data;
 405         struct stm_device *stm = stmf->stm;
 406         char *kbuf;
 407         int err;
 408
 409         /*
 410          * if no m/c have been assigned to this writer up to this
 411          * point, use "default" policy entry
 412          */
 413         if (!stmf->output.nr_chans) {
 414                 err = stm_file_assign(stmf, "default", 1);
 415                 /*
 416                  * EBUSY means that somebody else just assigned this
 417                  * output, which is just fine for write()
 418                  */
 419                 if (err && err != -EBUSY)
 420                         return err;
 421         }
 422
 423         kbuf = kmalloc(count + 1, GFP_KERNEL);
 424         if (!kbuf)
 425                 return -ENOMEM;
 426
 427         err = copy_from_user(kbuf, buf, count);
 428         if (err) {
 429                 kfree(kbuf);
 430                 return -EFAULT;
 431         }
 432
 433         stm_write(stm->data, stmf->output.master, stmf->output.channel, kbuf,
 434                   count);
 435
 436         kfree(kbuf);
 437
 438         return count;
 439 }
 440
 441 static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 442 {
 443         struct stm_file *stmf = file->private_data;
 444         struct stm_device *stm = stmf->stm;
 445         unsigned long size, phys;
 446
 447         if (!stm->data->mmio_addr)
 448                 return -EOPNOTSUPP;
 449
 450         if (vma->vm_pgoff)
 451                 return -EINVAL;
 452
 453         size = vma->vm_end - vma->vm_start;
 454
 455         if (stmf->output.nr_chans * stm->data->sw_mmiosz != size)
 456                 return -EINVAL;
 457
 458         phys = stm->data->mmio_addr(stm->data, stmf->output.master,
 459                                     stmf->output.channel,
 460                                     stmf->output.nr_chans);
 461
 462         if (!phys)
 463                 return -EINVAL;
 464
 465         vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 466         vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
 467         vm_iomap_memory(vma, phys, size);
 468
 469         return 0;
 470 }
 471
 472 static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
 473 {
 474         struct stm_device *stm = stmf->stm;
 475         struct stp_policy_id *id;
 476         int ret = -EINVAL;
 477         u32 size;
 478
 479         if (stmf->output.nr_chans)
 480                 return -EBUSY;
 481
 482         if (copy_from_user(&size, arg, sizeof(size)))
 483                 return -EFAULT;
 484
 485         if (size >= PATH_MAX + sizeof(*id))
 486                 return -EINVAL;
 487
 488         /*
 489          * size + 1 to make sure the .id string at the bottom is terminated,
 490          * which is also why memdup_user() is not useful here
 491          */
 492         id = kzalloc(size + 1, GFP_KERNEL);
 493         if (!id)
 494                 return -ENOMEM;
 495
 496         if (copy_from_user(id, arg, size)) {
 497                 ret = -EFAULT;
 498                 goto err_free;
 499         }
 500
 501         if (id->__reserved_0 || id->__reserved_1)
 502                 goto err_free;
 503
 504         if (id->width < 1 ||
 505             id->width > PAGE_SIZE / stm->data->sw_mmiosz)
 506                 goto err_free;
 507
 508         ret = stm_file_assign(stmf, id->id, id->width);
 509         if (ret)
 510                 goto err_free;
 511
 512         ret = 0;
 513
 514         if (stm->data->link)
 515                 ret = stm->data->link(stm->data, stmf->output.master,
 516                                       stmf->output.channel);
 517
 518         if (ret) {
 519                 stm_output_free(stmf->stm, &stmf->output);
 520                 stm_put_device(stmf->stm);
 521         }
 522
 523 err_free:
 524         kfree(id);
 525
 526         return ret;
 527 }
 528
 529 static int stm_char_policy_get_ioctl(struct stm_file *stmf, void __user *arg)
 530 {
 531         struct stp_policy_id id = {
 532                 .size           = sizeof(id),
 533                 .master         = stmf->output.master,
 534                 .channel        = stmf->output.channel,
 535                 .width          = stmf->output.nr_chans,
 536                 .__reserved_0   = 0,
 537                 .__reserved_1   = 0,
 538         };
 539
 540         return copy_to_user(arg, &id, id.size) ? -EFAULT : 0;
 541 }
 542
 543 static long
 544 stm_char_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 545 {
 546         struct stm_file *stmf = file->private_data;
 547         struct stm_data *stm_data = stmf->stm->data;
 548         int err = -ENOTTY;
 549         u64 options;
 550
 551         switch (cmd) {
 552         case STP_POLICY_ID_SET:
 553                 err = stm_char_policy_set_ioctl(stmf, (void __user *)arg);
 554                 if (err)
 555                         return err;
 556
 557                 return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 558
 559         case STP_POLICY_ID_GET:
 560                 return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 561
 562         case STP_SET_OPTIONS:
 563                 if (copy_from_user(&options, (u64 __user *)arg, sizeof(u64)))
 564                         return -EFAULT;
 565
 566                 if (stm_data->set_options)
 567                         err = stm_data->set_options(stm_data,
 568                                                     stmf->output.master,
 569                                                     stmf->output.channel,
 570                                                     stmf->output.nr_chans,
 571                                                     options);
 572
 573                 break;
 574         default:
 575                 break;
 576         }
 577
 578         return err;
 579 }
 580
 581 #ifdef CONFIG_COMPAT
 582 static long
 583 stm_char_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 584 {
 585         return stm_char_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
 586 }
 587 #else
 588 #define stm_char_compat_ioctl   NULL
 589 #endif
 590
 591 static const struct file_operations stm_fops = {
 592         .open           = stm_char_open,
 593         .release        = stm_char_release,
 594         .write          = stm_char_write,
 595         .mmap           = stm_char_mmap,
 596         .unlocked_ioctl = stm_char_ioctl,
 597         .compat_ioctl   = stm_char_compat_ioctl,
 598         .llseek         = no_llseek,
 599 };
 600
 601 static void stm_device_release(struct device *dev)
 602 {
 603         struct stm_device *stm = to_stm_device(dev);
 604
 605         kfree(stm);
 606 }
 607
 608 int stm_register_device(struct device *parent, struct stm_data *stm_data,
 609                         struct module *owner)
 610 {
 611         struct stm_device *stm;
 612         unsigned int nmasters;
 613         int err = -ENOMEM;
 614
 615         if (!stm_core_up)
 616                 return -EPROBE_DEFER;
 617
 618         if (!stm_data->packet || !stm_data->sw_nchannels)
 619                 return -EINVAL;
 620
 621         nmasters = stm_data->sw_end - stm_data->sw_start;
 622         stm = kzalloc(sizeof(*stm) + nmasters * sizeof(void *), GFP_KERNEL);
 623         if (!stm)
 624                 return -ENOMEM;
 625
 626         stm->major = register_chrdev(0, stm_data->name, &stm_fops);
 627         if (stm->major < 0)
 628                 goto err_free;
 629
 630         device_initialize(&stm->dev);
 631         stm->dev.devt = MKDEV(stm->major, 0);
 632         stm->dev.class = &stm_class;
 633         stm->dev.parent = parent;
 634         stm->dev.release = stm_device_release;
 635
 636         err = kobject_set_name(&stm->dev.kobj, "%s", stm_data->name);
 637         if (err)
 638                 goto err_device;
 639
 640         err = device_add(&stm->dev);
 641         if (err)
 642                 goto err_device;
 643
 644         spin_lock_init(&stm->link_lock);
 645         INIT_LIST_HEAD(&stm->link_list);
 646
 647         spin_lock_init(&stm->mc_lock);
 648         mutex_init(&stm->policy_mutex);
 649         stm->sw_nmasters = nmasters;
 650         stm->owner = owner;
 651         stm->data = stm_data;
 652         stm_data->stm = stm;
 653
 654         return 0;
 655
 656 err_device:
 657         put_device(&stm->dev);
 658 err_free:
 659         kfree(stm);
 660
 661         return err;
 662 }
 663 EXPORT_SYMBOL_GPL(stm_register_device);
 664
 665 static void __stm_source_link_drop(struct stm_source_device *src,
 666                                    struct stm_device *stm);
 667
 668 void stm_unregister_device(struct stm_data *stm_data)
 669 {
 670         struct stm_device *stm = stm_data->stm;
 671         struct stm_source_device *src, *iter;
 672         int i;
 673
 674         spin_lock(&stm->link_lock);
 675         list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {
 676                 __stm_source_link_drop(src, stm);
 677         }
 678         spin_unlock(&stm->link_lock);
 679
 680         synchronize_srcu(&stm_source_srcu);
 681
 682         unregister_chrdev(stm->major, stm_data->name);
 683
 684         mutex_lock(&stm->policy_mutex);
 685         if (stm->policy)
 686                 stp_policy_unbind(stm->policy);
 687         mutex_unlock(&stm->policy_mutex);
 688
 689         for (i = 0; i < stm->sw_nmasters; i++)
 690                 stp_master_free(stm, i);
 691
 692         device_unregister(&stm->dev);
 693         stm_data->stm = NULL;
 694 }
 695 EXPORT_SYMBOL_GPL(stm_unregister_device);
 696
 697 /**
 698  * stm_source_link_add() - connect an stm_source device to an stm device
 699  * @src:        stm_source device
 700  * @stm:        stm device
 701  *
 702  * This function establishes a link from stm_source to an stm device so that
 703  * the former can send out trace data to the latter.
 704  *
 705  * Return:      0 on success, -errno otherwise.
 706  */
 707 static int stm_source_link_add(struct stm_source_device *src,
 708                                struct stm_device *stm)
 709 {
 710         char *id;
 711         int err;
 712
 713         spin_lock(&stm->link_lock);
 714         spin_lock(&src->link_lock);
 715
 716         /* src->link is dereferenced under stm_source_srcu but not the list */
 717         rcu_assign_pointer(src->link, stm);
 718         list_add_tail(&src->link_entry, &stm->link_list);
 719
 720         spin_unlock(&src->link_lock);
 721         spin_unlock(&stm->link_lock);
 722
 723         id = kstrdup(src->data->name, GFP_KERNEL);
 724         if (id) {
 725                 src->policy_node =
 726                         stp_policy_node_lookup(stm, id);
 727
 728                 kfree(id);
 729         }
 730
 731         err = stm_output_assign(stm, src->data->nr_chans,
 732                                 src->policy_node, &src->output);
 733
 734         if (src->policy_node)
 735                 stp_policy_node_put(src->policy_node);
 736
 737         if (err)
 738                 goto fail_detach;
 739
 740         /* this is to notify the STM device that a new link has been made */
 741         if (stm->data->link)
 742                 err = stm->data->link(stm->data, src->output.master,
 743                                       src->output.channel);
 744
 745         if (err)
 746                 goto fail_free_output;
 747
 748         /* this is to let the source carry out all necessary preparations */
 749         if (src->data->link)
 750                 src->data->link(src->data);
 751
 752         return 0;
 753
 754 fail_free_output:
 755         stm_output_free(stm, &src->output);
 756         stm_put_device(stm);
 757
 758 fail_detach:
 759         spin_lock(&stm->link_lock);
 760         spin_lock(&src->link_lock);
 761
 762         rcu_assign_pointer(src->link, NULL);
 763         list_del_init(&src->link_entry);
 764
 765         spin_unlock(&src->link_lock);
 766         spin_unlock(&stm->link_lock);
 767
 768         return err;
 769 }
 770
 771 /**
 772  * __stm_source_link_drop() - detach stm_source from an stm device
 773  * @src:        stm_source device
 774  * @stm:        stm device
 775  *
 776  * If @stm is @src::link, disconnect them from one another and put the
 777  * reference on the @stm device.
 778  *
 779  * Caller must hold stm::link_lock.
 780  */
 781 static void __stm_source_link_drop(struct stm_source_device *src,
 782                                    struct stm_device *stm)
 783 {
 784         struct stm_device *link;
 785
 786         spin_lock(&src->link_lock);
 787         link = srcu_dereference_check(src->link, &stm_source_srcu, 1);
 788         if (WARN_ON_ONCE(link != stm)) {
 789                 spin_unlock(&src->link_lock);
 790                 return;
 791         }
 792
 793         stm_output_free(link, &src->output);
 794         /* caller must hold stm::link_lock */
 795         list_del_init(&src->link_entry);
 796         /* matches stm_find_device() from stm_source_link_store() */
 797         stm_put_device(link);
 798         rcu_assign_pointer(src->link, NULL);
 799
 800         spin_unlock(&src->link_lock);
 801 }
 802
 803 /**
 804  * stm_source_link_drop() - detach stm_source from its stm device
 805  * @src:        stm_source device
 806  *
 807  * Unlinking means disconnecting from source's STM device; after this
 808  * writes will be unsuccessful until it is linked to a new STM device.
 809  *
 810  * This will happen on "stm_source_link" sysfs attribute write to undo
 811  * the existing link (if any), or on linked STM device's de-registration.
 812  */
 813 static void stm_source_link_drop(struct stm_source_device *src)
 814 {
 815         struct stm_device *stm;
 816         int idx;
 817
 818         idx = srcu_read_lock(&stm_source_srcu);
 819         stm = srcu_dereference(src->link, &stm_source_srcu);
 820
 821         if (stm) {
 822                 if (src->data->unlink)
 823                         src->data->unlink(src->data);
 824
 825                 spin_lock(&stm->link_lock);
 826                 __stm_source_link_drop(src, stm);
 827                 spin_unlock(&stm->link_lock);
 828         }
 829
 830         srcu_read_unlock(&stm_source_srcu, idx);
 831 }
 832
 833 static ssize_t stm_source_link_show(struct device *dev,
 834                                     struct device_attribute *attr,
 835                                     char *buf)
 836 {
 837         struct stm_source_device *src = to_stm_source_device(dev);
 838         struct stm_device *stm;
 839         int idx, ret;
 840
 841         idx = srcu_read_lock(&stm_source_srcu);
 842         stm = srcu_dereference(src->link, &stm_source_srcu);
 843         ret = sprintf(buf, "%s\n",
 844                       stm ? dev_name(&stm->dev) : "<none>");
 845         srcu_read_unlock(&stm_source_srcu, idx);
 846
 847         return ret;
 848 }
 849
 850 static ssize_t stm_source_link_store(struct device *dev,
 851                                      struct device_attribute *attr,
 852                                      const char *buf, size_t count)
 853 {
 854         struct stm_source_device *src = to_stm_source_device(dev);
 855         struct stm_device *link;
 856         int err;
 857
 858         stm_source_link_drop(src);
 859
 860         link = stm_find_device(buf);
 861         if (!link)
 862                 return -EINVAL;
 863
 864         err = stm_source_link_add(src, link);
 865         if (err)
 866                 stm_put_device(link);
 867
 868         return err ? : count;
 869 }
 870
 871 static DEVICE_ATTR_RW(stm_source_link);
 872
 873 static struct attribute *stm_source_attrs[] = {
 874         &dev_attr_stm_source_link.attr,
 875         NULL,
 876 };
 877
 878 ATTRIBUTE_GROUPS(stm_source);
 879
 880 static struct class stm_source_class = {
 881         .name           = "stm_source",
 882         .dev_groups     = stm_source_groups,
 883 };
 884
 885 static void stm_source_device_release(struct device *dev)
 886 {
 887         struct stm_source_device *src = to_stm_source_device(dev);
 888
 889         kfree(src);
 890 }
 891
 892 /**
 893  * stm_source_register_device() - register an stm_source device
 894  * @parent:     parent device
 895  * @data:       device description structure
 896  *
 897  * This will create a device of stm_source class that can write
 898  * data to an stm device once linked.
 899  *
 900  * Return:      0 on success, -errno otherwise.
 901  */
 902 int stm_source_register_device(struct device *parent,
 903                                struct stm_source_data *data)
 904 {
 905         struct stm_source_device *src;
 906         int err;
 907
 908         if (!stm_core_up)
 909                 return -EPROBE_DEFER;
 910
 911         src = kzalloc(sizeof(*src), GFP_KERNEL);
 912         if (!src)
 913                 return -ENOMEM;
 914
 915         device_initialize(&src->dev);
 916         src->dev.class = &stm_source_class;
 917         src->dev.parent = parent;
 918         src->dev.release = stm_source_device_release;
 919
 920         err = kobject_set_name(&src->dev.kobj, "%s", data->name);
 921         if (err)
 922                 goto err;
 923
 924         err = device_add(&src->dev);
 925         if (err)
 926                 goto err;
 927
 928         spin_lock_init(&src->link_lock);
 929         INIT_LIST_HEAD(&src->link_entry);
 930         src->data = data;
 931         data->src = src;
 932
 933         return 0;
 934
 935 err:
 936         put_device(&src->dev);
 937         kfree(src);
 938
 939         return err;
 940 }
 941 EXPORT_SYMBOL_GPL(stm_source_register_device);
 942
 943 /**
 944  * stm_source_unregister_device() - unregister an stm_source device
 945  * @data:       device description that was used to register the device
 946  *
 947  * This will remove a previously created stm_source device from the system.
 948  */
 949 void stm_source_unregister_device(struct stm_source_data *data)
 950 {
 951         struct stm_source_device *src = data->src;
 952
 953         stm_source_link_drop(src);
 954
 955         device_destroy(&stm_source_class, src->dev.devt);
 956 }
 957 EXPORT_SYMBOL_GPL(stm_source_unregister_device);
 958
 959 int stm_source_write(struct stm_source_data *data, unsigned int chan,
 960                      const char *buf, size_t count)
 961 {
 962         struct stm_source_device *src = data->src;
 963         struct stm_device *stm;
 964         int idx;
 965
 966         if (!src->output.nr_chans)
 967                 return -ENODEV;
 968
 969         if (chan >= src->output.nr_chans)
 970                 return -EINVAL;
 971
 972         idx = srcu_read_lock(&stm_source_srcu);
 973
 974         stm = srcu_dereference(src->link, &stm_source_srcu);
 975         if (stm)
 976                 stm_write(stm->data, src->output.master,
 977                           src->output.channel + chan,
 978                           buf, count);
 979         else
 980                 count = -ENODEV;
 981
 982         srcu_read_unlock(&stm_source_srcu, idx);
 983
 984         return count;
 985 }
 986 EXPORT_SYMBOL_GPL(stm_source_write);
 987
 988 static int __init stm_core_init(void)
 989 {
 990         int err;
 991
 992         err = class_register(&stm_class);
 993         if (err)
 994                 return err;
 995
 996         err = class_register(&stm_source_class);
 997         if (err)
 998                 goto err_stm;
 999
1000         err = stp_configfs_init();
1001         if (err)
1002                 goto err_src;
1003
1004         init_srcu_struct(&stm_source_srcu);
1005
1006         stm_core_up++;
1007
1008         return 0;
1009
1010 err_src:
1011         class_unregister(&stm_source_class);
1012 err_stm:
1013         class_unregister(&stm_class);
1014
1015         return err;
1016 }
1017
1018 module_init(stm_core_init);
1019
1020 static void __exit stm_core_exit(void)
1021 {
1022         cleanup_srcu_struct(&stm_source_srcu);
1023         class_unregister(&stm_source_class);
1024         class_unregister(&stm_class);
1025         stp_configfs_exit();
1026 }
1027
1028 module_exit(stm_core_exit);
1029
1030 MODULE_LICENSE("GPL v2");
1031 MODULE_DESCRIPTION("System Trace Module device class");
1032 MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");