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         lockdep_assert_held(&stm->mc_lock);
 189         lockdep_assert_held(&output->lock);
 190
 191         if (WARN_ON_ONCE(master->nr_free < output->nr_chans))
 192                 return;
 193
 194         bitmap_allocate_region(&master->chan_map[0], output->channel,
 195                                ilog2(output->nr_chans));
 196
 197         master->nr_free -= output->nr_chans;
 198 }
 199
 200 static void
 201 stm_output_disclaim(struct stm_device *stm, struct stm_output *output)
 202 {
 203         struct stp_master *master = stm_master(stm, output->master);
 204
 205         lockdep_assert_held(&stm->mc_lock);
 206         lockdep_assert_held(&output->lock);
 207
 208         bitmap_release_region(&master->chan_map[0], output->channel,
 209                               ilog2(output->nr_chans));
 210
 211         output->nr_chans = 0;
 212         master->nr_free += output->nr_chans;
 213 }
 214
 215 /*
 216  * This is like bitmap_find_free_region(), except it can ignore @start bits
 217  * at the beginning.
 218  */
 219 static int find_free_channels(unsigned long *bitmap, unsigned int start,
 220                               unsigned int end, unsigned int width)
 221 {
 222         unsigned int pos;
 223         int i;
 224
 225         for (pos = start; pos < end + 1; pos = ALIGN(pos, width)) {
 226                 pos = find_next_zero_bit(bitmap, end + 1, pos);
 227                 if (pos + width > end + 1)
 228                         break;
 229
 230                 if (pos & (width - 1))
 231                         continue;
 232
 233                 for (i = 1; i < width && !test_bit(pos + i, bitmap); i++)
 234                         ;
 235                 if (i == width)
 236                         return pos;
 237         }
 238
 239         return -1;
 240 }
 241
 242 static unsigned int
 243 stm_find_master_chan(struct stm_device *stm, unsigned int width,
 244                      unsigned int *mstart, unsigned int mend,
 245                      unsigned int *cstart, unsigned int cend)
 246 {
 247         struct stp_master *master;
 248         unsigned int midx;
 249         int pos, err;
 250
 251         for (midx = *mstart; midx <= mend; midx++) {
 252                 if (!stm_master(stm, midx)) {
 253                         err = stp_master_alloc(stm, midx);
 254                         if (err)
 255                                 return err;
 256                 }
 257
 258                 master = stm_master(stm, midx);
 259
 260                 if (!master->nr_free)
 261                         continue;
 262
 263                 pos = find_free_channels(master->chan_map, *cstart, cend,
 264                                          width);
 265                 if (pos < 0)
 266                         continue;
 267
 268                 *mstart = midx;
 269                 *cstart = pos;
 270                 return 0;
 271         }
 272
 273         return -ENOSPC;
 274 }
 275
 276 static int stm_output_assign(struct stm_device *stm, unsigned int width,
 277                              struct stp_policy_node *policy_node,
 278                              struct stm_output *output)
 279 {
 280         unsigned int midx, cidx, mend, cend;
 281         int ret = -EINVAL;
 282
 283         if (width > stm->data->sw_nchannels)
 284                 return -EINVAL;
 285
 286         if (policy_node) {
 287                 stp_policy_node_get_ranges(policy_node,
 288                                            &midx, &mend, &cidx, &cend);
 289         } else {
 290                 midx = stm->data->sw_start;
 291                 cidx = 0;
 292                 mend = stm->data->sw_end;
 293                 cend = stm->data->sw_nchannels - 1;
 294         }
 295
 296         spin_lock(&stm->mc_lock);
 297         spin_lock(&output->lock);
 298         /* output is already assigned -- shouldn't happen */
 299         if (WARN_ON_ONCE(output->nr_chans))
 300                 goto unlock;
 301
 302         ret = stm_find_master_chan(stm, width, &midx, mend, &cidx, cend);
 303         if (ret)
 304                 goto unlock;
 305
 306         output->master = midx;
 307         output->channel = cidx;
 308         output->nr_chans = width;
 309         stm_output_claim(stm, output);
 310         dev_dbg(&stm->dev, "assigned %u:%u (+%u)\n", midx, cidx, width);
 311
 312         ret = 0;
 313 unlock:
 314         spin_unlock(&output->lock);
 315         spin_unlock(&stm->mc_lock);
 316
 317         return ret;
 318 }
 319
 320 static void stm_output_free(struct stm_device *stm, struct stm_output *output)
 321 {
 322         spin_lock(&stm->mc_lock);
 323         spin_lock(&output->lock);
 324         if (output->nr_chans)
 325                 stm_output_disclaim(stm, output);
 326         spin_unlock(&output->lock);
 327         spin_unlock(&stm->mc_lock);
 328 }
 329
 330 static void stm_output_init(struct stm_output *output)
 331 {
 332         spin_lock_init(&output->lock);
 333 }
 334
 335 static int major_match(struct device *dev, const void *data)
 336 {
 337         unsigned int major = *(unsigned int *)data;
 338
 339         return MAJOR(dev->devt) == major;
 340 }
 341
 342 static int stm_char_open(struct inode *inode, struct file *file)
 343 {
 344         struct stm_file *stmf;
 345         struct device *dev;
 346         unsigned int major = imajor(inode);
 347         int err = -ENODEV;
 348
 349         dev = class_find_device(&stm_class, NULL, &major, major_match);
 350         if (!dev)
 351                 return -ENODEV;
 352
 353         stmf = kzalloc(sizeof(*stmf), GFP_KERNEL);
 354         if (!stmf)
 355                 return -ENOMEM;
 356
 357         stm_output_init(&stmf->output);
 358         stmf->stm = to_stm_device(dev);
 359
 360         if (!try_module_get(stmf->stm->owner))
 361                 goto err_free;
 362
 363         file->private_data = stmf;
 364
 365         return nonseekable_open(inode, file);
 366
 367 err_free:
 368         kfree(stmf);
 369
 370         return err;
 371 }
 372
 373 static int stm_char_release(struct inode *inode, struct file *file)
 374 {
 375         struct stm_file *stmf = file->private_data;
 376
 377         stm_output_free(stmf->stm, &stmf->output);
 378         stm_put_device(stmf->stm);
 379         kfree(stmf);
 380
 381         return 0;
 382 }
 383
 384 static int stm_file_assign(struct stm_file *stmf, char *id, unsigned int width)
 385 {
 386         struct stm_device *stm = stmf->stm;
 387         int ret;
 388
 389         stmf->policy_node = stp_policy_node_lookup(stm, id);
 390
 391         ret = stm_output_assign(stm, width, stmf->policy_node, &stmf->output);
 392
 393         if (stmf->policy_node)
 394                 stp_policy_node_put(stmf->policy_node);
 395
 396         return ret;
 397 }
 398
 399 static ssize_t stm_write(struct stm_data *data, unsigned int master,
 400                           unsigned int channel, const char *buf, size_t count)
 401 {
 402         unsigned int flags = STP_PACKET_TIMESTAMPED;
 403         const unsigned char *p = buf, nil = 0;
 404         size_t pos;
 405         ssize_t sz;
 406
 407         for (pos = 0, p = buf; count > pos; pos += sz, p += sz) {
 408                 sz = min_t(unsigned int, count - pos, 8);
 409                 sz = data->packet(data, master, channel, STP_PACKET_DATA, flags,
 410                                   sz, p);
 411                 flags = 0;
 412
 413                 if (sz < 0)
 414                         break;
 415         }
 416
 417         data->packet(data, master, channel, STP_PACKET_FLAG, 0, 0, &nil);
 418
 419         return pos;
 420 }
 421
 422 static ssize_t stm_char_write(struct file *file, const char __user *buf,
 423                               size_t count, loff_t *ppos)
 424 {
 425         struct stm_file *stmf = file->private_data;
 426         struct stm_device *stm = stmf->stm;
 427         char *kbuf;
 428         int err;
 429
 430         if (count + 1 > PAGE_SIZE)
 431                 count = PAGE_SIZE - 1;
 432
 433         /*
 434          * if no m/c have been assigned to this writer up to this
 435          * point, use "default" policy entry
 436          */
 437         if (!stmf->output.nr_chans) {
 438                 err = stm_file_assign(stmf, "default", 1);
 439                 /*
 440                  * EBUSY means that somebody else just assigned this
 441                  * output, which is just fine for write()
 442                  */
 443                 if (err && err != -EBUSY)
 444                         return err;
 445         }
 446
 447         kbuf = kmalloc(count + 1, GFP_KERNEL);
 448         if (!kbuf)
 449                 return -ENOMEM;
 450
 451         err = copy_from_user(kbuf, buf, count);
 452         if (err) {
 453                 kfree(kbuf);
 454                 return -EFAULT;
 455         }
 456
 457         count = stm_write(stm->data, stmf->output.master, stmf->output.channel,
 458                           kbuf, count);
 459
 460         kfree(kbuf);
 461
 462         return count;
 463 }
 464
 465 static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 466 {
 467         struct stm_file *stmf = file->private_data;
 468         struct stm_device *stm = stmf->stm;
 469         unsigned long size, phys;
 470
 471         if (!stm->data->mmio_addr)
 472                 return -EOPNOTSUPP;
 473
 474         if (vma->vm_pgoff)
 475                 return -EINVAL;
 476
 477         size = vma->vm_end - vma->vm_start;
 478
 479         if (stmf->output.nr_chans * stm->data->sw_mmiosz != size)
 480                 return -EINVAL;
 481
 482         phys = stm->data->mmio_addr(stm->data, stmf->output.master,
 483                                     stmf->output.channel,
 484                                     stmf->output.nr_chans);
 485
 486         if (!phys)
 487                 return -EINVAL;
 488
 489         vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 490         vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
 491         vm_iomap_memory(vma, phys, size);
 492
 493         return 0;
 494 }
 495
 496 static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
 497 {
 498         struct stm_device *stm = stmf->stm;
 499         struct stp_policy_id *id;
 500         int ret = -EINVAL;
 501         u32 size;
 502
 503         if (stmf->output.nr_chans)
 504                 return -EBUSY;
 505
 506         if (copy_from_user(&size, arg, sizeof(size)))
 507                 return -EFAULT;
 508
 509         if (size >= PATH_MAX + sizeof(*id))
 510                 return -EINVAL;
 511
 512         /*
 513          * size + 1 to make sure the .id string at the bottom is terminated,
 514          * which is also why memdup_user() is not useful here
 515          */
 516         id = kzalloc(size + 1, GFP_KERNEL);
 517         if (!id)
 518                 return -ENOMEM;
 519
 520         if (copy_from_user(id, arg, size)) {
 521                 ret = -EFAULT;
 522                 goto err_free;
 523         }
 524
 525         if (id->__reserved_0 || id->__reserved_1)
 526                 goto err_free;
 527
 528         if (id->width < 1 ||
 529             id->width > PAGE_SIZE / stm->data->sw_mmiosz)
 530                 goto err_free;
 531
 532         ret = stm_file_assign(stmf, id->id, id->width);
 533         if (ret)
 534                 goto err_free;
 535
 536         ret = 0;
 537
 538         if (stm->data->link)
 539                 ret = stm->data->link(stm->data, stmf->output.master,
 540                                       stmf->output.channel);
 541
 542         if (ret) {
 543                 stm_output_free(stmf->stm, &stmf->output);
 544                 stm_put_device(stmf->stm);
 545         }
 546
 547 err_free:
 548         kfree(id);
 549
 550         return ret;
 551 }
 552
 553 static int stm_char_policy_get_ioctl(struct stm_file *stmf, void __user *arg)
 554 {
 555         struct stp_policy_id id = {
 556                 .size           = sizeof(id),
 557                 .master         = stmf->output.master,
 558                 .channel        = stmf->output.channel,
 559                 .width          = stmf->output.nr_chans,
 560                 .__reserved_0   = 0,
 561                 .__reserved_1   = 0,
 562         };
 563
 564         return copy_to_user(arg, &id, id.size) ? -EFAULT : 0;
 565 }
 566
 567 static long
 568 stm_char_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 569 {
 570         struct stm_file *stmf = file->private_data;
 571         struct stm_data *stm_data = stmf->stm->data;
 572         int err = -ENOTTY;
 573         u64 options;
 574
 575         switch (cmd) {
 576         case STP_POLICY_ID_SET:
 577                 err = stm_char_policy_set_ioctl(stmf, (void __user *)arg);
 578                 if (err)
 579                         return err;
 580
 581                 return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 582
 583         case STP_POLICY_ID_GET:
 584                 return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 585
 586         case STP_SET_OPTIONS:
 587                 if (copy_from_user(&options, (u64 __user *)arg, sizeof(u64)))
 588                         return -EFAULT;
 589
 590                 if (stm_data->set_options)
 591                         err = stm_data->set_options(stm_data,
 592                                                     stmf->output.master,
 593                                                     stmf->output.channel,
 594                                                     stmf->output.nr_chans,
 595                                                     options);
 596
 597                 break;
 598         default:
 599                 break;
 600         }
 601
 602         return err;
 603 }
 604
 605 #ifdef CONFIG_COMPAT
 606 static long
 607 stm_char_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 608 {
 609         return stm_char_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
 610 }
 611 #else
 612 #define stm_char_compat_ioctl   NULL
 613 #endif
 614
 615 static const struct file_operations stm_fops = {
 616         .open           = stm_char_open,
 617         .release        = stm_char_release,
 618         .write          = stm_char_write,
 619         .mmap           = stm_char_mmap,
 620         .unlocked_ioctl = stm_char_ioctl,
 621         .compat_ioctl   = stm_char_compat_ioctl,
 622         .llseek         = no_llseek,
 623 };
 624
 625 static void stm_device_release(struct device *dev)
 626 {
 627         struct stm_device *stm = to_stm_device(dev);
 628
 629         kfree(stm);
 630 }
 631
 632 int stm_register_device(struct device *parent, struct stm_data *stm_data,
 633                         struct module *owner)
 634 {
 635         struct stm_device *stm;
 636         unsigned int nmasters;
 637         int err = -ENOMEM;
 638
 639         if (!stm_core_up)
 640                 return -EPROBE_DEFER;
 641
 642         if (!stm_data->packet || !stm_data->sw_nchannels)
 643                 return -EINVAL;
 644
 645         nmasters = stm_data->sw_end - stm_data->sw_start;
 646         stm = kzalloc(sizeof(*stm) + nmasters * sizeof(void *), GFP_KERNEL);
 647         if (!stm)
 648                 return -ENOMEM;
 649
 650         stm->major = register_chrdev(0, stm_data->name, &stm_fops);
 651         if (stm->major < 0)
 652                 goto err_free;
 653
 654         device_initialize(&stm->dev);
 655         stm->dev.devt = MKDEV(stm->major, 0);
 656         stm->dev.class = &stm_class;
 657         stm->dev.parent = parent;
 658         stm->dev.release = stm_device_release;
 659
 660         err = kobject_set_name(&stm->dev.kobj, "%s", stm_data->name);
 661         if (err)
 662                 goto err_device;
 663
 664         err = device_add(&stm->dev);
 665         if (err)
 666                 goto err_device;
 667
 668         mutex_init(&stm->link_mutex);
 669         spin_lock_init(&stm->link_lock);
 670         INIT_LIST_HEAD(&stm->link_list);
 671
 672         spin_lock_init(&stm->mc_lock);
 673         mutex_init(&stm->policy_mutex);
 674         stm->sw_nmasters = nmasters;
 675         stm->owner = owner;
 676         stm->data = stm_data;
 677         stm_data->stm = stm;
 678
 679         return 0;
 680
 681 err_device:
 682         put_device(&stm->dev);
 683 err_free:
 684         kfree(stm);
 685
 686         return err;
 687 }
 688 EXPORT_SYMBOL_GPL(stm_register_device);
 689
 690 static void __stm_source_link_drop(struct stm_source_device *src,
 691                                    struct stm_device *stm);
 692
 693 void stm_unregister_device(struct stm_data *stm_data)
 694 {
 695         struct stm_device *stm = stm_data->stm;
 696         struct stm_source_device *src, *iter;
 697         int i;
 698
 699         mutex_lock(&stm->link_mutex);
 700         list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {
 701                 __stm_source_link_drop(src, stm);
 702         }
 703         mutex_unlock(&stm->link_mutex);
 704
 705         synchronize_srcu(&stm_source_srcu);
 706
 707         unregister_chrdev(stm->major, stm_data->name);
 708
 709         mutex_lock(&stm->policy_mutex);
 710         if (stm->policy)
 711                 stp_policy_unbind(stm->policy);
 712         mutex_unlock(&stm->policy_mutex);
 713
 714         for (i = 0; i < stm->sw_nmasters; i++)
 715                 stp_master_free(stm, i);
 716
 717         device_unregister(&stm->dev);
 718         stm_data->stm = NULL;
 719 }
 720 EXPORT_SYMBOL_GPL(stm_unregister_device);
 721
 722 /*
 723  * stm::link_list access serialization uses a spinlock and a mutex; holding
 724  * either of them guarantees that the list is stable; modification requires
 725  * holding both of them.
 726  *
 727  * Lock ordering is as follows:
 728  *   stm::link_mutex
 729  *     stm::link_lock
 730  *       src::link_lock
 731  */
 732
 733 /**
 734  * stm_source_link_add() - connect an stm_source device to an stm device
 735  * @src:        stm_source device
 736  * @stm:        stm device
 737  *
 738  * This function establishes a link from stm_source to an stm device so that
 739  * the former can send out trace data to the latter.
 740  *
 741  * Return:      0 on success, -errno otherwise.
 742  */
 743 static int stm_source_link_add(struct stm_source_device *src,
 744                                struct stm_device *stm)
 745 {
 746         char *id;
 747         int err;
 748
 749         mutex_lock(&stm->link_mutex);
 750         spin_lock(&stm->link_lock);
 751         spin_lock(&src->link_lock);
 752
 753         /* src->link is dereferenced under stm_source_srcu but not the list */
 754         rcu_assign_pointer(src->link, stm);
 755         list_add_tail(&src->link_entry, &stm->link_list);
 756
 757         spin_unlock(&src->link_lock);
 758         spin_unlock(&stm->link_lock);
 759         mutex_unlock(&stm->link_mutex);
 760
 761         id = kstrdup(src->data->name, GFP_KERNEL);
 762         if (id) {
 763                 src->policy_node =
 764                         stp_policy_node_lookup(stm, id);
 765
 766                 kfree(id);
 767         }
 768
 769         err = stm_output_assign(stm, src->data->nr_chans,
 770                                 src->policy_node, &src->output);
 771
 772         if (src->policy_node)
 773                 stp_policy_node_put(src->policy_node);
 774
 775         if (err)
 776                 goto fail_detach;
 777
 778         /* this is to notify the STM device that a new link has been made */
 779         if (stm->data->link)
 780                 err = stm->data->link(stm->data, src->output.master,
 781                                       src->output.channel);
 782
 783         if (err)
 784                 goto fail_free_output;
 785
 786         /* this is to let the source carry out all necessary preparations */
 787         if (src->data->link)
 788                 src->data->link(src->data);
 789
 790         return 0;
 791
 792 fail_free_output:
 793         stm_output_free(stm, &src->output);
 794         stm_put_device(stm);
 795
 796 fail_detach:
 797         mutex_lock(&stm->link_mutex);
 798         spin_lock(&stm->link_lock);
 799         spin_lock(&src->link_lock);
 800
 801         rcu_assign_pointer(src->link, NULL);
 802         list_del_init(&src->link_entry);
 803
 804         spin_unlock(&src->link_lock);
 805         spin_unlock(&stm->link_lock);
 806         mutex_unlock(&stm->link_mutex);
 807
 808         return err;
 809 }
 810
 811 /**
 812  * __stm_source_link_drop() - detach stm_source from an stm device
 813  * @src:        stm_source device
 814  * @stm:        stm device
 815  *
 816  * If @stm is @src::link, disconnect them from one another and put the
 817  * reference on the @stm device.
 818  *
 819  * Caller must hold stm::link_mutex.
 820  */
 821 static void __stm_source_link_drop(struct stm_source_device *src,
 822                                    struct stm_device *stm)
 823 {
 824         struct stm_device *link;
 825
 826         lockdep_assert_held(&stm->link_mutex);
 827
 828         if (src->data->unlink)
 829                 src->data->unlink(src->data);
 830
 831         /* for stm::link_list modification, we hold both mutex and spinlock */
 832         spin_lock(&stm->link_lock);
 833         spin_lock(&src->link_lock);
 834         link = srcu_dereference_check(src->link, &stm_source_srcu, 1);
 835         if (WARN_ON_ONCE(link != stm))
 836                 goto unlock;
 837
 838         stm_output_free(link, &src->output);
 839         list_del_init(&src->link_entry);
 840         /* matches stm_find_device() from stm_source_link_store() */
 841         stm_put_device(link);
 842         rcu_assign_pointer(src->link, NULL);
 843
 844 unlock:
 845         spin_unlock(&src->link_lock);
 846         spin_unlock(&stm->link_lock);
 847 }
 848
 849 /**
 850  * stm_source_link_drop() - detach stm_source from its stm device
 851  * @src:        stm_source device
 852  *
 853  * Unlinking means disconnecting from source's STM device; after this
 854  * writes will be unsuccessful until it is linked to a new STM device.
 855  *
 856  * This will happen on "stm_source_link" sysfs attribute write to undo
 857  * the existing link (if any), or on linked STM device's de-registration.
 858  */
 859 static void stm_source_link_drop(struct stm_source_device *src)
 860 {
 861         struct stm_device *stm;
 862         int idx;
 863
 864         idx = srcu_read_lock(&stm_source_srcu);
 865         stm = srcu_dereference(src->link, &stm_source_srcu);
 866
 867         if (stm) {
 868                 mutex_lock(&stm->link_mutex);
 869                 __stm_source_link_drop(src, stm);
 870                 mutex_unlock(&stm->link_mutex);
 871         }
 872
 873         srcu_read_unlock(&stm_source_srcu, idx);
 874 }
 875
 876 static ssize_t stm_source_link_show(struct device *dev,
 877                                     struct device_attribute *attr,
 878                                     char *buf)
 879 {
 880         struct stm_source_device *src = to_stm_source_device(dev);
 881         struct stm_device *stm;
 882         int idx, ret;
 883
 884         idx = srcu_read_lock(&stm_source_srcu);
 885         stm = srcu_dereference(src->link, &stm_source_srcu);
 886         ret = sprintf(buf, "%s\n",
 887                       stm ? dev_name(&stm->dev) : "<none>");
 888         srcu_read_unlock(&stm_source_srcu, idx);
 889
 890         return ret;
 891 }
 892
 893 static ssize_t stm_source_link_store(struct device *dev,
 894                                      struct device_attribute *attr,
 895                                      const char *buf, size_t count)
 896 {
 897         struct stm_source_device *src = to_stm_source_device(dev);
 898         struct stm_device *link;
 899         int err;
 900
 901         stm_source_link_drop(src);
 902
 903         link = stm_find_device(buf);
 904         if (!link)
 905                 return -EINVAL;
 906
 907         err = stm_source_link_add(src, link);
 908         if (err)
 909                 stm_put_device(link);
 910
 911         return err ? : count;
 912 }
 913
 914 static DEVICE_ATTR_RW(stm_source_link);
 915
 916 static struct attribute *stm_source_attrs[] = {
 917         &dev_attr_stm_source_link.attr,
 918         NULL,
 919 };
 920
 921 ATTRIBUTE_GROUPS(stm_source);
 922
 923 static struct class stm_source_class = {
 924         .name           = "stm_source",
 925         .dev_groups     = stm_source_groups,
 926 };
 927
 928 static void stm_source_device_release(struct device *dev)
 929 {
 930         struct stm_source_device *src = to_stm_source_device(dev);
 931
 932         kfree(src);
 933 }
 934
 935 /**
 936  * stm_source_register_device() - register an stm_source device
 937  * @parent:     parent device
 938  * @data:       device description structure
 939  *
 940  * This will create a device of stm_source class that can write
 941  * data to an stm device once linked.
 942  *
 943  * Return:      0 on success, -errno otherwise.
 944  */
 945 int stm_source_register_device(struct device *parent,
 946                                struct stm_source_data *data)
 947 {
 948         struct stm_source_device *src;
 949         int err;
 950
 951         if (!stm_core_up)
 952                 return -EPROBE_DEFER;
 953
 954         src = kzalloc(sizeof(*src), GFP_KERNEL);
 955         if (!src)
 956                 return -ENOMEM;
 957
 958         device_initialize(&src->dev);
 959         src->dev.class = &stm_source_class;
 960         src->dev.parent = parent;
 961         src->dev.release = stm_source_device_release;
 962
 963         err = kobject_set_name(&src->dev.kobj, "%s", data->name);
 964         if (err)
 965                 goto err;
 966
 967         err = device_add(&src->dev);
 968         if (err)
 969                 goto err;
 970
 971         stm_output_init(&src->output);
 972         spin_lock_init(&src->link_lock);
 973         INIT_LIST_HEAD(&src->link_entry);
 974         src->data = data;
 975         data->src = src;
 976
 977         return 0;
 978
 979 err:
 980         put_device(&src->dev);
 981         kfree(src);
 982
 983         return err;
 984 }
 985 EXPORT_SYMBOL_GPL(stm_source_register_device);
 986
 987 /**
 988  * stm_source_unregister_device() - unregister an stm_source device
 989  * @data:       device description that was used to register the device
 990  *
 991  * This will remove a previously created stm_source device from the system.
 992  */
 993 void stm_source_unregister_device(struct stm_source_data *data)
 994 {
 995         struct stm_source_device *src = data->src;
 996
 997         stm_source_link_drop(src);
 998
 999         device_destroy(&stm_source_class, src->dev.devt);
1000 }
1001 EXPORT_SYMBOL_GPL(stm_source_unregister_device);
1002
1003 int stm_source_write(struct stm_source_data *data, unsigned int chan,
1004                      const char *buf, size_t count)
1005 {
1006         struct stm_source_device *src = data->src;
1007         struct stm_device *stm;
1008         int idx;
1009
1010         if (!src->output.nr_chans)
1011                 return -ENODEV;
1012
1013         if (chan >= src->output.nr_chans)
1014                 return -EINVAL;
1015
1016         idx = srcu_read_lock(&stm_source_srcu);
1017
1018         stm = srcu_dereference(src->link, &stm_source_srcu);
1019         if (stm)
1020                 count = stm_write(stm->data, src->output.master,
1021                                   src->output.channel + chan,
1022                                   buf, count);
1023         else
1024                 count = -ENODEV;
1025
1026         srcu_read_unlock(&stm_source_srcu, idx);
1027
1028         return count;
1029 }
1030 EXPORT_SYMBOL_GPL(stm_source_write);
1031
1032 static int __init stm_core_init(void)
1033 {
1034         int err;
1035
1036         err = class_register(&stm_class);
1037         if (err)
1038                 return err;
1039
1040         err = class_register(&stm_source_class);
1041         if (err)
1042                 goto err_stm;
1043
1044         err = stp_configfs_init();
1045         if (err)
1046                 goto err_src;
1047
1048         init_srcu_struct(&stm_source_srcu);
1049
1050         stm_core_up++;
1051
1052         return 0;
1053
1054 err_src:
1055         class_unregister(&stm_source_class);
1056 err_stm:
1057         class_unregister(&stm_class);
1058
1059         return err;
1060 }
1061
1062 module_init(stm_core_init);
1063
1064 static void __exit stm_core_exit(void)
1065 {
1066         cleanup_srcu_struct(&stm_source_srcu);
1067         class_unregister(&stm_source_class);
1068         class_unregister(&stm_class);
1069         stp_configfs_exit();
1070 }
1071
1072 module_exit(stm_core_exit);
1073
1074 MODULE_LICENSE("GPL v2");
1075 MODULE_DESCRIPTION("System Trace Module device class");
1076 MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");