drivers/hwtracing/stm/core.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * System Trace Module (STM) infrastructure
   4  * Copyright (c) 2014, Intel Corporation.
   5  *
   6  * STM class implements generic infrastructure for  System Trace Module devices
   7  * as defined in MIPI STPv2 specification.
   8  */
   9
  10 #include <linux/pm_runtime.h>
  11 #include <linux/uaccess.h>
  12 #include <linux/kernel.h>
  13 #include <linux/module.h>
  14 #include <linux/device.h>
  15 #include <linux/compat.h>
  16 #include <linux/kdev_t.h>
  17 #include <linux/srcu.h>
  18 #include <linux/slab.h>
  19 #include <linux/stm.h>
  20 #include <linux/fs.h>
  21 #include <linux/mm.h>
  22 #include <linux/vmalloc.h>
  23 #include "stm.h"
  24
  25 #include <uapi/linux/stm.h>
  26
  27 static unsigned int stm_core_up;
  28
  29 /*
  30  * The SRCU here makes sure that STM device doesn't disappear from under a
  31  * stm_source_write() caller, which may want to have as little overhead as
  32  * possible.
  33  */
  34 static struct srcu_struct stm_source_srcu;
  35
  36 static ssize_t masters_show(struct device *dev,
  37                             struct device_attribute *attr,
  38                             char *buf)
  39 {
  40         struct stm_device *stm = to_stm_device(dev);
  41         int ret;
  42
  43         ret = sprintf(buf, "%u %u\n", stm->data->sw_start, stm->data->sw_end);
  44
  45         return ret;
  46 }
  47
  48 static DEVICE_ATTR_RO(masters);
  49
  50 static ssize_t channels_show(struct device *dev,
  51                              struct device_attribute *attr,
  52                              char *buf)
  53 {
  54         struct stm_device *stm = to_stm_device(dev);
  55         int ret;
  56
  57         ret = sprintf(buf, "%u\n", stm->data->sw_nchannels);
  58
  59         return ret;
  60 }
  61
  62 static DEVICE_ATTR_RO(channels);
  63
  64 static ssize_t hw_override_show(struct device *dev,
  65                                 struct device_attribute *attr,
  66                                 char *buf)
  67 {
  68         struct stm_device *stm = to_stm_device(dev);
  69         int ret;
  70
  71         ret = sprintf(buf, "%u\n", stm->data->hw_override);
  72
  73         return ret;
  74 }
  75
  76 static DEVICE_ATTR_RO(hw_override);
  77
  78 static struct attribute *stm_attrs[] = {
  79         &dev_attr_masters.attr,
  80         &dev_attr_channels.attr,
  81         &dev_attr_hw_override.attr,
  82         NULL,
  83 };
  84
  85 ATTRIBUTE_GROUPS(stm);
  86
  87 static struct class stm_class = {
  88         .name           = "stm",
  89         .dev_groups     = stm_groups,
  90 };
  91
  92 static int stm_dev_match(struct device *dev, const void *data)
  93 {
  94         const char *name = data;
  95
  96         return sysfs_streq(name, dev_name(dev));
  97 }
  98
  99 /**
 100  * stm_find_device() - find stm device by name
 101  * @buf:        character buffer containing the name
 102  *
 103  * This is called when either policy gets assigned to an stm device or an
 104  * stm_source device gets linked to an stm device.
 105  *
 106  * This grabs device's reference (get_device()) and module reference, both
 107  * of which the calling path needs to make sure to drop with stm_put_device().
 108  *
 109  * Return:      stm device pointer or null if lookup failed.
 110  */
 111 struct stm_device *stm_find_device(const char *buf)
 112 {
 113         struct stm_device *stm;
 114         struct device *dev;
 115
 116         if (!stm_core_up)
 117                 return NULL;
 118
 119         dev = class_find_device(&stm_class, NULL, buf, stm_dev_match);
 120         if (!dev)
 121                 return NULL;
 122
 123         stm = to_stm_device(dev);
 124         if (!try_module_get(stm->owner)) {
 125                 /* matches class_find_device() above */
 126                 put_device(dev);
 127                 return NULL;
 128         }
 129
 130         return stm;
 131 }
 132
 133 /**
 134  * stm_put_device() - drop references on the stm device
 135  * @stm:        stm device, previously acquired by stm_find_device()
 136  *
 137  * This drops the module reference and device reference taken by
 138  * stm_find_device() or stm_char_open().
 139  */
 140 void stm_put_device(struct stm_device *stm)
 141 {
 142         module_put(stm->owner);
 143         put_device(&stm->dev);
 144 }
 145
 146 /*
 147  * Internally we only care about software-writable masters here, that is the
 148  * ones in the range [stm_data->sw_start..stm_data..sw_end], however we need
 149  * original master numbers to be visible externally, since they are the ones
 150  * that will appear in the STP stream. Thus, the internal bookkeeping uses
 151  * $master - stm_data->sw_start to reference master descriptors and such.
 152  */
 153
 154 #define __stm_master(_s, _m)                            \
 155         ((_s)->masters[(_m) - (_s)->data->sw_start])
 156
 157 static inline struct stp_master *
 158 stm_master(struct stm_device *stm, unsigned int idx)
 159 {
 160         if (idx < stm->data->sw_start || idx > stm->data->sw_end)
 161                 return NULL;
 162
 163         return __stm_master(stm, idx);
 164 }
 165
 166 static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
 167 {
 168         struct stp_master *master;
 169         size_t size;
 170
 171         size = ALIGN(stm->data->sw_nchannels, 8) / 8;
 172         size += sizeof(struct stp_master);
 173         master = kzalloc(size, GFP_ATOMIC);
 174         if (!master)
 175                 return -ENOMEM;
 176
 177         master->nr_free = stm->data->sw_nchannels;
 178         __stm_master(stm, idx) = master;
 179
 180         return 0;
 181 }
 182
 183 static void stp_master_free(struct stm_device *stm, unsigned int idx)
 184 {
 185         struct stp_master *master = stm_master(stm, idx);
 186
 187         if (!master)
 188                 return;
 189
 190         __stm_master(stm, idx) = NULL;
 191         kfree(master);
 192 }
 193
 194 static void stm_output_claim(struct stm_device *stm, struct stm_output *output)
 195 {
 196         struct stp_master *master = stm_master(stm, output->master);
 197
 198         lockdep_assert_held(&stm->mc_lock);
 199         lockdep_assert_held(&output->lock);
 200
 201         if (WARN_ON_ONCE(master->nr_free < output->nr_chans))
 202                 return;
 203
 204         bitmap_allocate_region(&master->chan_map[0], output->channel,
 205                                ilog2(output->nr_chans));
 206
 207         master->nr_free -= output->nr_chans;
 208 }
 209
 210 static void
 211 stm_output_disclaim(struct stm_device *stm, struct stm_output *output)
 212 {
 213         struct stp_master *master = stm_master(stm, output->master);
 214
 215         lockdep_assert_held(&stm->mc_lock);
 216         lockdep_assert_held(&output->lock);
 217
 218         bitmap_release_region(&master->chan_map[0], output->channel,
 219                               ilog2(output->nr_chans));
 220
 221         output->nr_chans = 0;
 222         master->nr_free += output->nr_chans;
 223 }
 224
 225 /*
 226  * This is like bitmap_find_free_region(), except it can ignore @start bits
 227  * at the beginning.
 228  */
 229 static int find_free_channels(unsigned long *bitmap, unsigned int start,
 230                               unsigned int end, unsigned int width)
 231 {
 232         unsigned int pos;
 233         int i;
 234
 235         for (pos = start; pos < end + 1; pos = ALIGN(pos, width)) {
 236                 pos = find_next_zero_bit(bitmap, end + 1, pos);
 237                 if (pos + width > end + 1)
 238                         break;
 239
 240                 if (pos & (width - 1))
 241                         continue;
 242
 243                 for (i = 1; i < width && !test_bit(pos + i, bitmap); i++)
 244                         ;
 245                 if (i == width)
 246                         return pos;
 247         }
 248
 249         return -1;
 250 }
 251
 252 static int
 253 stm_find_master_chan(struct stm_device *stm, unsigned int width,
 254                      unsigned int *mstart, unsigned int mend,
 255                      unsigned int *cstart, unsigned int cend)
 256 {
 257         struct stp_master *master;
 258         unsigned int midx;
 259         int pos, err;
 260
 261         for (midx = *mstart; midx <= mend; midx++) {
 262                 if (!stm_master(stm, midx)) {
 263                         err = stp_master_alloc(stm, midx);
 264                         if (err)
 265                                 return err;
 266                 }
 267
 268                 master = stm_master(stm, midx);
 269
 270                 if (!master->nr_free)
 271                         continue;
 272
 273                 pos = find_free_channels(master->chan_map, *cstart, cend,
 274                                          width);
 275                 if (pos < 0)
 276                         continue;
 277
 278                 *mstart = midx;
 279                 *cstart = pos;
 280                 return 0;
 281         }
 282
 283         return -ENOSPC;
 284 }
 285
 286 static int stm_output_assign(struct stm_device *stm, unsigned int width,
 287                              struct stp_policy_node *policy_node,
 288                              struct stm_output *output)
 289 {
 290         unsigned int midx, cidx, mend, cend;
 291         int ret = -EINVAL;
 292
 293         if (width > stm->data->sw_nchannels)
 294                 return -EINVAL;
 295
 296         if (policy_node) {
 297                 stp_policy_node_get_ranges(policy_node,
 298                                            &midx, &mend, &cidx, &cend);
 299         } else {
 300                 midx = stm->data->sw_start;
 301                 cidx = 0;
 302                 mend = stm->data->sw_end;
 303                 cend = stm->data->sw_nchannels - 1;
 304         }
 305
 306         spin_lock(&stm->mc_lock);
 307         spin_lock(&output->lock);
 308         /* output is already assigned -- shouldn't happen */
 309         if (WARN_ON_ONCE(output->nr_chans))
 310                 goto unlock;
 311
 312         ret = stm_find_master_chan(stm, width, &midx, mend, &cidx, cend);
 313         if (ret < 0)
 314                 goto unlock;
 315
 316         output->master = midx;
 317         output->channel = cidx;
 318         output->nr_chans = width;
 319         stm_output_claim(stm, output);
 320         dev_dbg(&stm->dev, "assigned %u:%u (+%u)\n", midx, cidx, width);
 321
 322         ret = 0;
 323 unlock:
 324         spin_unlock(&output->lock);
 325         spin_unlock(&stm->mc_lock);
 326
 327         return ret;
 328 }
 329
 330 static void stm_output_free(struct stm_device *stm, struct stm_output *output)
 331 {
 332         spin_lock(&stm->mc_lock);
 333         spin_lock(&output->lock);
 334         if (output->nr_chans)
 335                 stm_output_disclaim(stm, output);
 336         spin_unlock(&output->lock);
 337         spin_unlock(&stm->mc_lock);
 338 }
 339
 340 static void stm_output_init(struct stm_output *output)
 341 {
 342         spin_lock_init(&output->lock);
 343 }
 344
 345 static int major_match(struct device *dev, const void *data)
 346 {
 347         unsigned int major = *(unsigned int *)data;
 348
 349         return MAJOR(dev->devt) == major;
 350 }
 351
 352 static int stm_char_open(struct inode *inode, struct file *file)
 353 {
 354         struct stm_file *stmf;
 355         struct device *dev;
 356         unsigned int major = imajor(inode);
 357         int err = -ENOMEM;
 358
 359         dev = class_find_device(&stm_class, NULL, &major, major_match);
 360         if (!dev)
 361                 return -ENODEV;
 362
 363         stmf = kzalloc(sizeof(*stmf), GFP_KERNEL);
 364         if (!stmf)
 365                 goto err_put_device;
 366
 367         err = -ENODEV;
 368         stm_output_init(&stmf->output);
 369         stmf->stm = to_stm_device(dev);
 370
 371         if (!try_module_get(stmf->stm->owner))
 372                 goto err_free;
 373
 374         file->private_data = stmf;
 375
 376         return nonseekable_open(inode, file);
 377
 378 err_free:
 379         kfree(stmf);
 380 err_put_device:
 381         /* matches class_find_device() above */
 382         put_device(dev);
 383
 384         return err;
 385 }
 386
 387 static int stm_char_release(struct inode *inode, struct file *file)
 388 {
 389         struct stm_file *stmf = file->private_data;
 390         struct stm_device *stm = stmf->stm;
 391
 392         if (stm->data->unlink)
 393                 stm->data->unlink(stm->data, stmf->output.master,
 394                                   stmf->output.channel);
 395
 396         stm_output_free(stm, &stmf->output);
 397
 398         /*
 399          * matches the stm_char_open()'s
 400          * class_find_device() + try_module_get()
 401          */
 402         stm_put_device(stm);
 403         kfree(stmf);
 404
 405         return 0;
 406 }
 407
 408 static int stm_file_assign(struct stm_file *stmf, char *id, unsigned int width)
 409 {
 410         struct stm_device *stm = stmf->stm;
 411         int ret;
 412
 413         stmf->policy_node = stp_policy_node_lookup(stm, id);
 414
 415         ret = stm_output_assign(stm, width, stmf->policy_node, &stmf->output);
 416
 417         if (stmf->policy_node)
 418                 stp_policy_node_put(stmf->policy_node);
 419
 420         return ret;
 421 }
 422
 423 static ssize_t notrace stm_write(struct stm_data *data, unsigned int master,
 424                           unsigned int channel, const char *buf, size_t count)
 425 {
 426         unsigned int flags = STP_PACKET_TIMESTAMPED;
 427         const unsigned char *p = buf, nil = 0;
 428         size_t pos;
 429         ssize_t sz;
 430
 431         for (pos = 0, p = buf; count > pos; pos += sz, p += sz) {
 432                 sz = min_t(unsigned int, count - pos, 8);
 433                 sz = data->packet(data, master, channel, STP_PACKET_DATA, flags,
 434                                   sz, p);
 435                 flags = 0;
 436
 437                 if (sz < 0)
 438                         break;
 439         }
 440
 441         data->packet(data, master, channel, STP_PACKET_FLAG, 0, 0, &nil);
 442
 443         return pos;
 444 }
 445
 446 static ssize_t stm_char_write(struct file *file, const char __user *buf,
 447                               size_t count, loff_t *ppos)
 448 {
 449         struct stm_file *stmf = file->private_data;
 450         struct stm_device *stm = stmf->stm;
 451         char *kbuf;
 452         int err;
 453
 454         if (count + 1 > PAGE_SIZE)
 455                 count = PAGE_SIZE - 1;
 456
 457         /*
 458          * if no m/c have been assigned to this writer up to this
 459          * point, use "default" policy entry
 460          */
 461         if (!stmf->output.nr_chans) {
 462                 err = stm_file_assign(stmf, "default", 1);
 463                 /*
 464                  * EBUSY means that somebody else just assigned this
 465                  * output, which is just fine for write()
 466                  */
 467                 if (err && err != -EBUSY)
 468                         return err;
 469         }
 470
 471         kbuf = kmalloc(count + 1, GFP_KERNEL);
 472         if (!kbuf)
 473                 return -ENOMEM;
 474
 475         err = copy_from_user(kbuf, buf, count);
 476         if (err) {
 477                 kfree(kbuf);
 478                 return -EFAULT;
 479         }
 480
 481         pm_runtime_get_sync(&stm->dev);
 482
 483         count = stm_write(stm->data, stmf->output.master, stmf->output.channel,
 484                           kbuf, count);
 485
 486         pm_runtime_mark_last_busy(&stm->dev);
 487         pm_runtime_put_autosuspend(&stm->dev);
 488         kfree(kbuf);
 489
 490         return count;
 491 }
 492
 493 static void stm_mmap_open(struct vm_area_struct *vma)
 494 {
 495         struct stm_file *stmf = vma->vm_file->private_data;
 496         struct stm_device *stm = stmf->stm;
 497
 498         pm_runtime_get(&stm->dev);
 499 }
 500
 501 static void stm_mmap_close(struct vm_area_struct *vma)
 502 {
 503         struct stm_file *stmf = vma->vm_file->private_data;
 504         struct stm_device *stm = stmf->stm;
 505
 506         pm_runtime_mark_last_busy(&stm->dev);
 507         pm_runtime_put_autosuspend(&stm->dev);
 508 }
 509
 510 static const struct vm_operations_struct stm_mmap_vmops = {
 511         .open   = stm_mmap_open,
 512         .close  = stm_mmap_close,
 513 };
 514
 515 static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 516 {
 517         struct stm_file *stmf = file->private_data;
 518         struct stm_device *stm = stmf->stm;
 519         unsigned long size, phys;
 520
 521         if (!stm->data->mmio_addr)
 522                 return -EOPNOTSUPP;
 523
 524         if (vma->vm_pgoff)
 525                 return -EINVAL;
 526
 527         size = vma->vm_end - vma->vm_start;
 528
 529         if (stmf->output.nr_chans * stm->data->sw_mmiosz != size)
 530                 return -EINVAL;
 531
 532         phys = stm->data->mmio_addr(stm->data, stmf->output.master,
 533                                     stmf->output.channel,
 534                                     stmf->output.nr_chans);
 535
 536         if (!phys)
 537                 return -EINVAL;
 538
 539         pm_runtime_get_sync(&stm->dev);
 540
 541         vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 542         vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
 543         vma->vm_ops = &stm_mmap_vmops;
 544         vm_iomap_memory(vma, phys, size);
 545
 546         return 0;
 547 }
 548
 549 static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
 550 {
 551         struct stm_device *stm = stmf->stm;
 552         struct stp_policy_id *id;
 553         int ret = -EINVAL;
 554         u32 size;
 555
 556         if (stmf->output.nr_chans)
 557                 return -EBUSY;
 558
 559         if (copy_from_user(&size, arg, sizeof(size)))
 560                 return -EFAULT;
 561
 562         if (size < sizeof(*id) || size >= PATH_MAX + sizeof(*id))
 563                 return -EINVAL;
 564
 565         /*
 566          * size + 1 to make sure the .id string at the bottom is terminated,
 567          * which is also why memdup_user() is not useful here
 568          */
 569         id = kzalloc(size + 1, GFP_KERNEL);
 570         if (!id)
 571                 return -ENOMEM;
 572
 573         if (copy_from_user(id, arg, size)) {
 574                 ret = -EFAULT;
 575                 goto err_free;
 576         }
 577
 578         if (id->__reserved_0 || id->__reserved_1)
 579                 goto err_free;
 580
 581         if (id->width < 1 ||
 582             id->width > PAGE_SIZE / stm->data->sw_mmiosz)
 583                 goto err_free;
 584
 585         ret = stm_file_assign(stmf, id->id, id->width);
 586         if (ret)
 587                 goto err_free;
 588
 589         if (stm->data->link)
 590                 ret = stm->data->link(stm->data, stmf->output.master,
 591                                       stmf->output.channel);
 592
 593         if (ret)
 594                 stm_output_free(stmf->stm, &stmf->output);
 595
 596 err_free:
 597         kfree(id);
 598
 599         return ret;
 600 }
 601
 602 static int stm_char_policy_get_ioctl(struct stm_file *stmf, void __user *arg)
 603 {
 604         struct stp_policy_id id = {
 605                 .size           = sizeof(id),
 606                 .master         = stmf->output.master,
 607                 .channel        = stmf->output.channel,
 608                 .width          = stmf->output.nr_chans,
 609                 .__reserved_0   = 0,
 610                 .__reserved_1   = 0,
 611         };
 612
 613         return copy_to_user(arg, &id, id.size) ? -EFAULT : 0;
 614 }
 615
 616 static long
 617 stm_char_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 618 {
 619         struct stm_file *stmf = file->private_data;
 620         struct stm_data *stm_data = stmf->stm->data;
 621         int err = -ENOTTY;
 622         u64 options;
 623
 624         switch (cmd) {
 625         case STP_POLICY_ID_SET:
 626                 err = stm_char_policy_set_ioctl(stmf, (void __user *)arg);
 627                 if (err)
 628                         return err;
 629
 630                 return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 631
 632         case STP_POLICY_ID_GET:
 633                 return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 634
 635         case STP_SET_OPTIONS:
 636                 if (copy_from_user(&options, (u64 __user *)arg, sizeof(u64)))
 637                         return -EFAULT;
 638
 639                 if (stm_data->set_options)
 640                         err = stm_data->set_options(stm_data,
 641                                                     stmf->output.master,
 642                                                     stmf->output.channel,
 643                                                     stmf->output.nr_chans,
 644                                                     options);
 645
 646                 break;
 647         default:
 648                 break;
 649         }
 650
 651         return err;
 652 }
 653
 654 #ifdef CONFIG_COMPAT
 655 static long
 656 stm_char_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 657 {
 658         return stm_char_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
 659 }
 660 #else
 661 #define stm_char_compat_ioctl   NULL
 662 #endif
 663
 664 static const struct file_operations stm_fops = {
 665         .open           = stm_char_open,
 666         .release        = stm_char_release,
 667         .write          = stm_char_write,
 668         .mmap           = stm_char_mmap,
 669         .unlocked_ioctl = stm_char_ioctl,
 670         .compat_ioctl   = stm_char_compat_ioctl,
 671         .llseek         = no_llseek,
 672 };
 673
 674 static void stm_device_release(struct device *dev)
 675 {
 676         struct stm_device *stm = to_stm_device(dev);
 677
 678         vfree(stm);
 679 }
 680
 681 int stm_register_device(struct device *parent, struct stm_data *stm_data,
 682                         struct module *owner)
 683 {
 684         struct stm_device *stm;
 685         unsigned int nmasters;
 686         int err = -ENOMEM;
 687
 688         if (!stm_core_up)
 689                 return -EPROBE_DEFER;
 690
 691         if (!stm_data->packet || !stm_data->sw_nchannels)
 692                 return -EINVAL;
 693
 694         nmasters = stm_data->sw_end - stm_data->sw_start + 1;
 695         stm = vzalloc(sizeof(*stm) + nmasters * sizeof(void *));
 696         if (!stm)
 697                 return -ENOMEM;
 698
 699         stm->major = register_chrdev(0, stm_data->name, &stm_fops);
 700         if (stm->major < 0)
 701                 goto err_free;
 702
 703         device_initialize(&stm->dev);
 704         stm->dev.devt = MKDEV(stm->major, 0);
 705         stm->dev.class = &stm_class;
 706         stm->dev.parent = parent;
 707         stm->dev.release = stm_device_release;
 708
 709         mutex_init(&stm->link_mutex);
 710         spin_lock_init(&stm->link_lock);
 711         INIT_LIST_HEAD(&stm->link_list);
 712
 713         /* initialize the object before it is accessible via sysfs */
 714         spin_lock_init(&stm->mc_lock);
 715         mutex_init(&stm->policy_mutex);
 716         stm->sw_nmasters = nmasters;
 717         stm->owner = owner;
 718         stm->data = stm_data;
 719         stm_data->stm = stm;
 720
 721         err = kobject_set_name(&stm->dev.kobj, "%s", stm_data->name);
 722         if (err)
 723                 goto err_device;
 724
 725         err = device_add(&stm->dev);
 726         if (err)
 727                 goto err_device;
 728
 729         /*
 730          * Use delayed autosuspend to avoid bouncing back and forth
 731          * on recurring character device writes, with the initial
 732          * delay time of 2 seconds.
 733          */
 734         pm_runtime_no_callbacks(&stm->dev);
 735         pm_runtime_use_autosuspend(&stm->dev);
 736         pm_runtime_set_autosuspend_delay(&stm->dev, 2000);
 737         pm_runtime_set_suspended(&stm->dev);
 738         pm_runtime_enable(&stm->dev);
 739
 740         return 0;
 741
 742 err_device:
 743         unregister_chrdev(stm->major, stm_data->name);
 744
 745         /* matches device_initialize() above */
 746         put_device(&stm->dev);
 747 err_free:
 748         vfree(stm);
 749
 750         return err;
 751 }
 752 EXPORT_SYMBOL_GPL(stm_register_device);
 753
 754 static int __stm_source_link_drop(struct stm_source_device *src,
 755                                   struct stm_device *stm);
 756
 757 void stm_unregister_device(struct stm_data *stm_data)
 758 {
 759         struct stm_device *stm = stm_data->stm;
 760         struct stm_source_device *src, *iter;
 761         int i, ret;
 762
 763         pm_runtime_dont_use_autosuspend(&stm->dev);
 764         pm_runtime_disable(&stm->dev);
 765
 766         mutex_lock(&stm->link_mutex);
 767         list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {
 768                 ret = __stm_source_link_drop(src, stm);
 769                 /*
 770                  * src <-> stm link must not change under the same
 771                  * stm::link_mutex, so complain loudly if it has;
 772                  * also in this situation ret!=0 means this src is
 773                  * not connected to this stm and it should be otherwise
 774                  * safe to proceed with the tear-down of stm.
 775                  */
 776                 WARN_ON_ONCE(ret);
 777         }
 778         mutex_unlock(&stm->link_mutex);
 779
 780         synchronize_srcu(&stm_source_srcu);
 781
 782         unregister_chrdev(stm->major, stm_data->name);
 783
 784         mutex_lock(&stm->policy_mutex);
 785         if (stm->policy)
 786                 stp_policy_unbind(stm->policy);
 787         mutex_unlock(&stm->policy_mutex);
 788
 789         for (i = stm->data->sw_start; i <= stm->data->sw_end; i++)
 790                 stp_master_free(stm, i);
 791
 792         device_unregister(&stm->dev);
 793         stm_data->stm = NULL;
 794 }
 795 EXPORT_SYMBOL_GPL(stm_unregister_device);
 796
 797 /*
 798  * stm::link_list access serialization uses a spinlock and a mutex; holding
 799  * either of them guarantees that the list is stable; modification requires
 800  * holding both of them.
 801  *
 802  * Lock ordering is as follows:
 803  *   stm::link_mutex
 804  *     stm::link_lock
 805  *       src::link_lock
 806  */
 807
 808 /**
 809  * stm_source_link_add() - connect an stm_source device to an stm device
 810  * @src:        stm_source device
 811  * @stm:        stm device
 812  *
 813  * This function establishes a link from stm_source to an stm device so that
 814  * the former can send out trace data to the latter.
 815  *
 816  * Return:      0 on success, -errno otherwise.
 817  */
 818 static int stm_source_link_add(struct stm_source_device *src,
 819                                struct stm_device *stm)
 820 {
 821         char *id;
 822         int err;
 823
 824         mutex_lock(&stm->link_mutex);
 825         spin_lock(&stm->link_lock);
 826         spin_lock(&src->link_lock);
 827
 828         /* src->link is dereferenced under stm_source_srcu but not the list */
 829         rcu_assign_pointer(src->link, stm);
 830         list_add_tail(&src->link_entry, &stm->link_list);
 831
 832         spin_unlock(&src->link_lock);
 833         spin_unlock(&stm->link_lock);
 834         mutex_unlock(&stm->link_mutex);
 835
 836         id = kstrdup(src->data->name, GFP_KERNEL);
 837         if (id) {
 838                 src->policy_node =
 839                         stp_policy_node_lookup(stm, id);
 840
 841                 kfree(id);
 842         }
 843
 844         err = stm_output_assign(stm, src->data->nr_chans,
 845                                 src->policy_node, &src->output);
 846
 847         if (src->policy_node)
 848                 stp_policy_node_put(src->policy_node);
 849
 850         if (err)
 851                 goto fail_detach;
 852
 853         /* this is to notify the STM device that a new link has been made */
 854         if (stm->data->link)
 855                 err = stm->data->link(stm->data, src->output.master,
 856                                       src->output.channel);
 857
 858         if (err)
 859                 goto fail_free_output;
 860
 861         /* this is to let the source carry out all necessary preparations */
 862         if (src->data->link)
 863                 src->data->link(src->data);
 864
 865         return 0;
 866
 867 fail_free_output:
 868         stm_output_free(stm, &src->output);
 869
 870 fail_detach:
 871         mutex_lock(&stm->link_mutex);
 872         spin_lock(&stm->link_lock);
 873         spin_lock(&src->link_lock);
 874
 875         rcu_assign_pointer(src->link, NULL);
 876         list_del_init(&src->link_entry);
 877
 878         spin_unlock(&src->link_lock);
 879         spin_unlock(&stm->link_lock);
 880         mutex_unlock(&stm->link_mutex);
 881
 882         return err;
 883 }
 884
 885 /**
 886  * __stm_source_link_drop() - detach stm_source from an stm device
 887  * @src:        stm_source device
 888  * @stm:        stm device
 889  *
 890  * If @stm is @src::link, disconnect them from one another and put the
 891  * reference on the @stm device.
 892  *
 893  * Caller must hold stm::link_mutex.
 894  */
 895 static int __stm_source_link_drop(struct stm_source_device *src,
 896                                   struct stm_device *stm)
 897 {
 898         struct stm_device *link;
 899         int ret = 0;
 900
 901         lockdep_assert_held(&stm->link_mutex);
 902
 903         /* for stm::link_list modification, we hold both mutex and spinlock */
 904         spin_lock(&stm->link_lock);
 905         spin_lock(&src->link_lock);
 906         link = srcu_dereference_check(src->link, &stm_source_srcu, 1);
 907
 908         /*
 909          * The linked device may have changed since we last looked, because
 910          * we weren't holding the src::link_lock back then; if this is the
 911          * case, tell the caller to retry.
 912          */
 913         if (link != stm) {
 914                 ret = -EAGAIN;
 915                 goto unlock;
 916         }
 917
 918         stm_output_free(link, &src->output);
 919         list_del_init(&src->link_entry);
 920         pm_runtime_mark_last_busy(&link->dev);
 921         pm_runtime_put_autosuspend(&link->dev);
 922         /* matches stm_find_device() from stm_source_link_store() */
 923         stm_put_device(link);
 924         rcu_assign_pointer(src->link, NULL);
 925
 926 unlock:
 927         spin_unlock(&src->link_lock);
 928         spin_unlock(&stm->link_lock);
 929
 930         /*
 931          * Call the unlink callbacks for both source and stm, when we know
 932          * that we have actually performed the unlinking.
 933          */
 934         if (!ret) {
 935                 if (src->data->unlink)
 936                         src->data->unlink(src->data);
 937
 938                 if (stm->data->unlink)
 939                         stm->data->unlink(stm->data, src->output.master,
 940                                           src->output.channel);
 941         }
 942
 943         return ret;
 944 }
 945
 946 /**
 947  * stm_source_link_drop() - detach stm_source from its stm device
 948  * @src:        stm_source device
 949  *
 950  * Unlinking means disconnecting from source's STM device; after this
 951  * writes will be unsuccessful until it is linked to a new STM device.
 952  *
 953  * This will happen on "stm_source_link" sysfs attribute write to undo
 954  * the existing link (if any), or on linked STM device's de-registration.
 955  */
 956 static void stm_source_link_drop(struct stm_source_device *src)
 957 {
 958         struct stm_device *stm;
 959         int idx, ret;
 960
 961 retry:
 962         idx = srcu_read_lock(&stm_source_srcu);
 963         /*
 964          * The stm device will be valid for the duration of this
 965          * read section, but the link may change before we grab
 966          * the src::link_lock in __stm_source_link_drop().
 967          */
 968         stm = srcu_dereference(src->link, &stm_source_srcu);
 969
 970         ret = 0;
 971         if (stm) {
 972                 mutex_lock(&stm->link_mutex);
 973                 ret = __stm_source_link_drop(src, stm);
 974                 mutex_unlock(&stm->link_mutex);
 975         }
 976
 977         srcu_read_unlock(&stm_source_srcu, idx);
 978
 979         /* if it did change, retry */
 980         if (ret == -EAGAIN)
 981                 goto retry;
 982 }
 983
 984 static ssize_t stm_source_link_show(struct device *dev,
 985                                     struct device_attribute *attr,
 986                                     char *buf)
 987 {
 988         struct stm_source_device *src = to_stm_source_device(dev);
 989         struct stm_device *stm;
 990         int idx, ret;
 991
 992         idx = srcu_read_lock(&stm_source_srcu);
 993         stm = srcu_dereference(src->link, &stm_source_srcu);
 994         ret = sprintf(buf, "%s\n",
 995                       stm ? dev_name(&stm->dev) : "<none>");
 996         srcu_read_unlock(&stm_source_srcu, idx);
 997
 998         return ret;
 999 }
1000
1001 static ssize_t stm_source_link_store(struct device *dev,
1002                                      struct device_attribute *attr,
1003                                      const char *buf, size_t count)
1004 {
1005         struct stm_source_device *src = to_stm_source_device(dev);
1006         struct stm_device *link;
1007         int err;
1008
1009         stm_source_link_drop(src);
1010
1011         link = stm_find_device(buf);
1012         if (!link)
1013                 return -EINVAL;
1014
1015         pm_runtime_get(&link->dev);
1016
1017         err = stm_source_link_add(src, link);
1018         if (err) {
1019                 pm_runtime_put_autosuspend(&link->dev);
1020                 /* matches the stm_find_device() above */
1021                 stm_put_device(link);
1022         }
1023
1024         return err ? : count;
1025 }
1026
1027 static DEVICE_ATTR_RW(stm_source_link);
1028
1029 static struct attribute *stm_source_attrs[] = {
1030         &dev_attr_stm_source_link.attr,
1031         NULL,
1032 };
1033
1034 ATTRIBUTE_GROUPS(stm_source);
1035
1036 static struct class stm_source_class = {
1037         .name           = "stm_source",
1038         .dev_groups     = stm_source_groups,
1039 };
1040
1041 static void stm_source_device_release(struct device *dev)
1042 {
1043         struct stm_source_device *src = to_stm_source_device(dev);
1044
1045         kfree(src);
1046 }
1047
1048 /**
1049  * stm_source_register_device() - register an stm_source device
1050  * @parent:     parent device
1051  * @data:       device description structure
1052  *
1053  * This will create a device of stm_source class that can write
1054  * data to an stm device once linked.
1055  *
1056  * Return:      0 on success, -errno otherwise.
1057  */
1058 int stm_source_register_device(struct device *parent,
1059                                struct stm_source_data *data)
1060 {
1061         struct stm_source_device *src;
1062         int err;
1063
1064         if (!stm_core_up)
1065                 return -EPROBE_DEFER;
1066
1067         src = kzalloc(sizeof(*src), GFP_KERNEL);
1068         if (!src)
1069                 return -ENOMEM;
1070
1071         device_initialize(&src->dev);
1072         src->dev.class = &stm_source_class;
1073         src->dev.parent = parent;
1074         src->dev.release = stm_source_device_release;
1075
1076         err = kobject_set_name(&src->dev.kobj, "%s", data->name);
1077         if (err)
1078                 goto err;
1079
1080         pm_runtime_no_callbacks(&src->dev);
1081         pm_runtime_forbid(&src->dev);
1082
1083         err = device_add(&src->dev);
1084         if (err)
1085                 goto err;
1086
1087         stm_output_init(&src->output);
1088         spin_lock_init(&src->link_lock);
1089         INIT_LIST_HEAD(&src->link_entry);
1090         src->data = data;
1091         data->src = src;
1092
1093         return 0;
1094
1095 err:
1096         put_device(&src->dev);
1097         kfree(src);
1098
1099         return err;
1100 }
1101 EXPORT_SYMBOL_GPL(stm_source_register_device);
1102
1103 /**
1104  * stm_source_unregister_device() - unregister an stm_source device
1105  * @data:       device description that was used to register the device
1106  *
1107  * This will remove a previously created stm_source device from the system.
1108  */
1109 void stm_source_unregister_device(struct stm_source_data *data)
1110 {
1111         struct stm_source_device *src = data->src;
1112
1113         stm_source_link_drop(src);
1114
1115         device_unregister(&src->dev);
1116 }
1117 EXPORT_SYMBOL_GPL(stm_source_unregister_device);
1118
1119 int notrace stm_source_write(struct stm_source_data *data,
1120                              unsigned int chan,
1121                              const char *buf, size_t count)
1122 {
1123         struct stm_source_device *src = data->src;
1124         struct stm_device *stm;
1125         int idx;
1126
1127         if (!src->output.nr_chans)
1128                 return -ENODEV;
1129
1130         if (chan >= src->output.nr_chans)
1131                 return -EINVAL;
1132
1133         idx = srcu_read_lock(&stm_source_srcu);
1134
1135         stm = srcu_dereference(src->link, &stm_source_srcu);
1136         if (stm)
1137                 count = stm_write(stm->data, src->output.master,
1138                                   src->output.channel + chan,
1139                                   buf, count);
1140         else
1141                 count = -ENODEV;
1142
1143         srcu_read_unlock(&stm_source_srcu, idx);
1144
1145         return count;
1146 }
1147 EXPORT_SYMBOL_GPL(stm_source_write);
1148
1149 static int __init stm_core_init(void)
1150 {
1151         int err;
1152
1153         err = class_register(&stm_class);
1154         if (err)
1155                 return err;
1156
1157         err = class_register(&stm_source_class);
1158         if (err)
1159                 goto err_stm;
1160
1161         err = stp_configfs_init();
1162         if (err)
1163                 goto err_src;
1164
1165         init_srcu_struct(&stm_source_srcu);
1166
1167         stm_core_up++;
1168
1169         return 0;
1170
1171 err_src:
1172         class_unregister(&stm_source_class);
1173 err_stm:
1174         class_unregister(&stm_class);
1175
1176         return err;
1177 }
1178
1179 module_init(stm_core_init);
1180
1181 static void __exit stm_core_exit(void)
1182 {
1183         cleanup_srcu_struct(&stm_source_srcu);
1184         class_unregister(&stm_source_class);
1185         class_unregister(&stm_class);
1186         stp_configfs_exit();
1187 }
1188
1189 module_exit(stm_core_exit);
1190
1191 MODULE_LICENSE("GPL v2");
1192 MODULE_DESCRIPTION("System Trace Module device class");
1193 MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");