drivers/dma-buf/dma-fence.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Fence mechanism for dma-buf and to allow for asynchronous dma access
   4  *
   5  * Copyright (C) 2012 Canonical Ltd
   6  * Copyright (C) 2012 Texas Instruments
   7  *
   8  * Authors:
   9  * Rob Clark <robdclark@gmail.com>
  10  * Maarten Lankhorst <maarten.lankhorst@canonical.com>
  11  */
  12
  13 #include <linux/slab.h>
  14 #include <linux/export.h>
  15 #include <linux/atomic.h>
  16 #include <linux/dma-fence.h>
  17 #include <linux/sched/signal.h>
  18
  19 #define CREATE_TRACE_POINTS
  20 #include <trace/events/dma_fence.h>
  21
  22 EXPORT_TRACEPOINT_SYMBOL(dma_fence_emit);
  23 EXPORT_TRACEPOINT_SYMBOL(dma_fence_enable_signal);
  24 EXPORT_TRACEPOINT_SYMBOL(dma_fence_signaled);
  25
  26 static DEFINE_SPINLOCK(dma_fence_stub_lock);
  27 static struct dma_fence dma_fence_stub;
  28
  29 /*
  30  * fence context counter: each execution context should have its own
  31  * fence context, this allows checking if fences belong to the same
  32  * context or not. One device can have multiple separate contexts,
  33  * and they're used if some engine can run independently of another.
  34  */
  35 static atomic64_t dma_fence_context_counter = ATOMIC64_INIT(1);
  36
  37 /**
  38  * DOC: DMA fences overview
  39  *
  40  * DMA fences, represented by &struct dma_fence, are the kernel internal
  41  * synchronization primitive for DMA operations like GPU rendering, video
  42  * encoding/decoding, or displaying buffers on a screen.
  43  *
  44  * A fence is initialized using dma_fence_init() and completed using
  45  * dma_fence_signal(). Fences are associated with a context, allocated through
  46  * dma_fence_context_alloc(), and all fences on the same context are
  47  * fully ordered.
  48  *
  49  * Since the purposes of fences is to facilitate cross-device and
  50  * cross-application synchronization, there's multiple ways to use one:
  51  *
  52  * - Individual fences can be exposed as a &sync_file, accessed as a file
  53  *   descriptor from userspace, created by calling sync_file_create(). This is
  54  *   called explicit fencing, since userspace passes around explicit
  55  *   synchronization points.
  56  *
  57  * - Some subsystems also have their own explicit fencing primitives, like
  58  *   &drm_syncobj. Compared to &sync_file, a &drm_syncobj allows the underlying
  59  *   fence to be updated.
  60  *
  61  * - Then there's also implicit fencing, where the synchronization points are
  62  *   implicitly passed around as part of shared &dma_buf instances. Such
  63  *   implicit fences are stored in &struct reservation_object through the
  64  *   &dma_buf.resv pointer.
  65  */
  66
  67 static const char *dma_fence_stub_get_name(struct dma_fence *fence)
  68 {
  69         return "stub";
  70 }
  71
  72 static const struct dma_fence_ops dma_fence_stub_ops = {
  73         .get_driver_name = dma_fence_stub_get_name,
  74         .get_timeline_name = dma_fence_stub_get_name,
  75 };
  76
  77 /**
  78  * dma_fence_get_stub - return a signaled fence
  79  *
  80  * Return a stub fence which is already signaled.
  81  */
  82 struct dma_fence *dma_fence_get_stub(void)
  83 {
  84         spin_lock(&dma_fence_stub_lock);
  85         if (!dma_fence_stub.ops) {
  86                 dma_fence_init(&dma_fence_stub,
  87                                &dma_fence_stub_ops,
  88                                &dma_fence_stub_lock,
  89                                0, 0);
  90                 dma_fence_signal_locked(&dma_fence_stub);
  91         }
  92         spin_unlock(&dma_fence_stub_lock);
  93
  94         return dma_fence_get(&dma_fence_stub);
  95 }
  96 EXPORT_SYMBOL(dma_fence_get_stub);
  97
  98 /**
  99  * dma_fence_context_alloc - allocate an array of fence contexts
 100  * @num: amount of contexts to allocate
 101  *
 102  * This function will return the first index of the number of fence contexts
 103  * allocated.  The fence context is used for setting &dma_fence.context to a
 104  * unique number by passing the context to dma_fence_init().
 105  */
 106 u64 dma_fence_context_alloc(unsigned num)
 107 {
 108         WARN_ON(!num);
 109         return atomic64_add_return(num, &dma_fence_context_counter) - num;
 110 }
 111 EXPORT_SYMBOL(dma_fence_context_alloc);
 112
 113 /**
 114  * dma_fence_signal_locked - signal completion of a fence
 115  * @fence: the fence to signal
 116  *
 117  * Signal completion for software callbacks on a fence, this will unblock
 118  * dma_fence_wait() calls and run all the callbacks added with
 119  * dma_fence_add_callback(). Can be called multiple times, but since a fence
 120  * can only go from the unsignaled to the signaled state and not back, it will
 121  * only be effective the first time.
 122  *
 123  * Unlike dma_fence_signal(), this function must be called with &dma_fence.lock
 124  * held.
 125  *
 126  * Returns 0 on success and a negative error value when @fence has been
 127  * signalled already.
 128  */
 129 int dma_fence_signal_locked(struct dma_fence *fence)
 130 {
 131         struct dma_fence_cb *cur, *tmp;
 132         int ret = 0;
 133
 134         lockdep_assert_held(fence->lock);
 135
 136         if (WARN_ON(!fence))
 137                 return -EINVAL;
 138
 139         if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
 140                 ret = -EINVAL;
 141
 142                 /*
 143                  * we might have raced with the unlocked dma_fence_signal,
 144                  * still run through all callbacks
 145                  */
 146         } else {
 147                 fence->timestamp = ktime_get();
 148                 set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
 149                 trace_dma_fence_signaled(fence);
 150         }
 151
 152         list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
 153                 list_del_init(&cur->node);
 154                 cur->func(fence, cur);
 155         }
 156         return ret;
 157 }
 158 EXPORT_SYMBOL(dma_fence_signal_locked);
 159
 160 /**
 161  * dma_fence_signal - signal completion of a fence
 162  * @fence: the fence to signal
 163  *
 164  * Signal completion for software callbacks on a fence, this will unblock
 165  * dma_fence_wait() calls and run all the callbacks added with
 166  * dma_fence_add_callback(). Can be called multiple times, but since a fence
 167  * can only go from the unsignaled to the signaled state and not back, it will
 168  * only be effective the first time.
 169  *
 170  * Returns 0 on success and a negative error value when @fence has been
 171  * signalled already.
 172  */
 173 int dma_fence_signal(struct dma_fence *fence)
 174 {
 175         unsigned long flags;
 176
 177         if (!fence)
 178                 return -EINVAL;
 179
 180         if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 181                 return -EINVAL;
 182
 183         fence->timestamp = ktime_get();
 184         set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
 185         trace_dma_fence_signaled(fence);
 186
 187         if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) {
 188                 struct dma_fence_cb *cur, *tmp;
 189
 190                 spin_lock_irqsave(fence->lock, flags);
 191                 list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
 192                         list_del_init(&cur->node);
 193                         cur->func(fence, cur);
 194                 }
 195                 spin_unlock_irqrestore(fence->lock, flags);
 196         }
 197         return 0;
 198 }
 199 EXPORT_SYMBOL(dma_fence_signal);
 200
 201 /**
 202  * dma_fence_wait_timeout - sleep until the fence gets signaled
 203  * or until timeout elapses
 204  * @fence: the fence to wait on
 205  * @intr: if true, do an interruptible wait
 206  * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
 207  *
 208  * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
 209  * remaining timeout in jiffies on success. Other error values may be
 210  * returned on custom implementations.
 211  *
 212  * Performs a synchronous wait on this fence. It is assumed the caller
 213  * directly or indirectly (buf-mgr between reservation and committing)
 214  * holds a reference to the fence, otherwise the fence might be
 215  * freed before return, resulting in undefined behavior.
 216  *
 217  * See also dma_fence_wait() and dma_fence_wait_any_timeout().
 218  */
 219 signed long
 220 dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
 221 {
 222         signed long ret;
 223
 224         if (WARN_ON(timeout < 0))
 225                 return -EINVAL;
 226
 227         trace_dma_fence_wait_start(fence);
 228         if (fence->ops->wait)
 229                 ret = fence->ops->wait(fence, intr, timeout);
 230         else
 231                 ret = dma_fence_default_wait(fence, intr, timeout);
 232         trace_dma_fence_wait_end(fence);
 233         return ret;
 234 }
 235 EXPORT_SYMBOL(dma_fence_wait_timeout);
 236
 237 /**
 238  * dma_fence_release - default relese function for fences
 239  * @kref: &dma_fence.recfount
 240  *
 241  * This is the default release functions for &dma_fence. Drivers shouldn't call
 242  * this directly, but instead call dma_fence_put().
 243  */
 244 void dma_fence_release(struct kref *kref)
 245 {
 246         struct dma_fence *fence =
 247                 container_of(kref, struct dma_fence, refcount);
 248
 249         trace_dma_fence_destroy(fence);
 250
 251         /* Failed to signal before release, could be a refcounting issue */
 252         WARN_ON(!list_empty(&fence->cb_list));
 253
 254         if (fence->ops->release)
 255                 fence->ops->release(fence);
 256         else
 257                 dma_fence_free(fence);
 258 }
 259 EXPORT_SYMBOL(dma_fence_release);
 260
 261 /**
 262  * dma_fence_free - default release function for &dma_fence.
 263  * @fence: fence to release
 264  *
 265  * This is the default implementation for &dma_fence_ops.release. It calls
 266  * kfree_rcu() on @fence.
 267  */
 268 void dma_fence_free(struct dma_fence *fence)
 269 {
 270         kfree_rcu(fence, rcu);
 271 }
 272 EXPORT_SYMBOL(dma_fence_free);
 273
 274 /**
 275  * dma_fence_enable_sw_signaling - enable signaling on fence
 276  * @fence: the fence to enable
 277  *
 278  * This will request for sw signaling to be enabled, to make the fence
 279  * complete as soon as possible. This calls &dma_fence_ops.enable_signaling
 280  * internally.
 281  */
 282 void dma_fence_enable_sw_signaling(struct dma_fence *fence)
 283 {
 284         unsigned long flags;
 285
 286         if (!test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
 287                               &fence->flags) &&
 288             !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
 289             fence->ops->enable_signaling) {
 290                 trace_dma_fence_enable_signal(fence);
 291
 292                 spin_lock_irqsave(fence->lock, flags);
 293
 294                 if (!fence->ops->enable_signaling(fence))
 295                         dma_fence_signal_locked(fence);
 296
 297                 spin_unlock_irqrestore(fence->lock, flags);
 298         }
 299 }
 300 EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
 301
 302 /**
 303  * dma_fence_add_callback - add a callback to be called when the fence
 304  * is signaled
 305  * @fence: the fence to wait on
 306  * @cb: the callback to register
 307  * @func: the function to call
 308  *
 309  * @cb will be initialized by dma_fence_add_callback(), no initialization
 310  * by the caller is required. Any number of callbacks can be registered
 311  * to a fence, but a callback can only be registered to one fence at a time.
 312  *
 313  * Note that the callback can be called from an atomic context.  If
 314  * fence is already signaled, this function will return -ENOENT (and
 315  * *not* call the callback).
 316  *
 317  * Add a software callback to the fence. Same restrictions apply to
 318  * refcount as it does to dma_fence_wait(), however the caller doesn't need to
 319  * keep a refcount to fence afterward dma_fence_add_callback() has returned:
 320  * when software access is enabled, the creator of the fence is required to keep
 321  * the fence alive until after it signals with dma_fence_signal(). The callback
 322  * itself can be called from irq context.
 323  *
 324  * Returns 0 in case of success, -ENOENT if the fence is already signaled
 325  * and -EINVAL in case of error.
 326  */
 327 int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
 328                            dma_fence_func_t func)
 329 {
 330         unsigned long flags;
 331         int ret = 0;
 332         bool was_set;
 333
 334         if (WARN_ON(!fence || !func))
 335                 return -EINVAL;
 336
 337         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
 338                 INIT_LIST_HEAD(&cb->node);
 339                 return -ENOENT;
 340         }
 341
 342         spin_lock_irqsave(fence->lock, flags);
 343
 344         was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
 345                                    &fence->flags);
 346
 347         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 348                 ret = -ENOENT;
 349         else if (!was_set && fence->ops->enable_signaling) {
 350                 trace_dma_fence_enable_signal(fence);
 351
 352                 if (!fence->ops->enable_signaling(fence)) {
 353                         dma_fence_signal_locked(fence);
 354                         ret = -ENOENT;
 355                 }
 356         }
 357
 358         if (!ret) {
 359                 cb->func = func;
 360                 list_add_tail(&cb->node, &fence->cb_list);
 361         } else
 362                 INIT_LIST_HEAD(&cb->node);
 363         spin_unlock_irqrestore(fence->lock, flags);
 364
 365         return ret;
 366 }
 367 EXPORT_SYMBOL(dma_fence_add_callback);
 368
 369 /**
 370  * dma_fence_get_status - returns the status upon completion
 371  * @fence: the dma_fence to query
 372  *
 373  * This wraps dma_fence_get_status_locked() to return the error status
 374  * condition on a signaled fence. See dma_fence_get_status_locked() for more
 375  * details.
 376  *
 377  * Returns 0 if the fence has not yet been signaled, 1 if the fence has
 378  * been signaled without an error condition, or a negative error code
 379  * if the fence has been completed in err.
 380  */
 381 int dma_fence_get_status(struct dma_fence *fence)
 382 {
 383         unsigned long flags;
 384         int status;
 385
 386         spin_lock_irqsave(fence->lock, flags);
 387         status = dma_fence_get_status_locked(fence);
 388         spin_unlock_irqrestore(fence->lock, flags);
 389
 390         return status;
 391 }
 392 EXPORT_SYMBOL(dma_fence_get_status);
 393
 394 /**
 395  * dma_fence_remove_callback - remove a callback from the signaling list
 396  * @fence: the fence to wait on
 397  * @cb: the callback to remove
 398  *
 399  * Remove a previously queued callback from the fence. This function returns
 400  * true if the callback is successfully removed, or false if the fence has
 401  * already been signaled.
 402  *
 403  * *WARNING*:
 404  * Cancelling a callback should only be done if you really know what you're
 405  * doing, since deadlocks and race conditions could occur all too easily. For
 406  * this reason, it should only ever be done on hardware lockup recovery,
 407  * with a reference held to the fence.
 408  *
 409  * Behaviour is undefined if @cb has not been added to @fence using
 410  * dma_fence_add_callback() beforehand.
 411  */
 412 bool
 413 dma_fence_remove_callback(struct dma_fence *fence, struct dma_fence_cb *cb)
 414 {
 415         unsigned long flags;
 416         bool ret;
 417
 418         spin_lock_irqsave(fence->lock, flags);
 419
 420         ret = !list_empty(&cb->node);
 421         if (ret)
 422                 list_del_init(&cb->node);
 423
 424         spin_unlock_irqrestore(fence->lock, flags);
 425
 426         return ret;
 427 }
 428 EXPORT_SYMBOL(dma_fence_remove_callback);
 429
 430 struct default_wait_cb {
 431         struct dma_fence_cb base;
 432         struct task_struct *task;
 433 };
 434
 435 static void
 436 dma_fence_default_wait_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
 437 {
 438         struct default_wait_cb *wait =
 439                 container_of(cb, struct default_wait_cb, base);
 440
 441         wake_up_state(wait->task, TASK_NORMAL);
 442 }
 443
 444 /**
 445  * dma_fence_default_wait - default sleep until the fence gets signaled
 446  * or until timeout elapses
 447  * @fence: the fence to wait on
 448  * @intr: if true, do an interruptible wait
 449  * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
 450  *
 451  * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
 452  * remaining timeout in jiffies on success. If timeout is zero the value one is
 453  * returned if the fence is already signaled for consistency with other
 454  * functions taking a jiffies timeout.
 455  */
 456 signed long
 457 dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
 458 {
 459         struct default_wait_cb cb;
 460         unsigned long flags;
 461         signed long ret = timeout ? timeout : 1;
 462         bool was_set;
 463
 464         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 465                 return ret;
 466
 467         spin_lock_irqsave(fence->lock, flags);
 468
 469         if (intr && signal_pending(current)) {
 470                 ret = -ERESTARTSYS;
 471                 goto out;
 472         }
 473
 474         was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
 475                                    &fence->flags);
 476
 477         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 478                 goto out;
 479
 480         if (!was_set && fence->ops->enable_signaling) {
 481                 trace_dma_fence_enable_signal(fence);
 482
 483                 if (!fence->ops->enable_signaling(fence)) {
 484                         dma_fence_signal_locked(fence);
 485                         goto out;
 486                 }
 487         }
 488
 489         if (!timeout) {
 490                 ret = 0;
 491                 goto out;
 492         }
 493
 494         cb.base.func = dma_fence_default_wait_cb;
 495         cb.task = current;
 496         list_add(&cb.base.node, &fence->cb_list);
 497
 498         while (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) && ret > 0) {
 499                 if (intr)
 500                         __set_current_state(TASK_INTERRUPTIBLE);
 501                 else
 502                         __set_current_state(TASK_UNINTERRUPTIBLE);
 503                 spin_unlock_irqrestore(fence->lock, flags);
 504
 505                 ret = schedule_timeout(ret);
 506
 507                 spin_lock_irqsave(fence->lock, flags);
 508                 if (ret > 0 && intr && signal_pending(current))
 509                         ret = -ERESTARTSYS;
 510         }
 511
 512         if (!list_empty(&cb.base.node))
 513                 list_del(&cb.base.node);
 514         __set_current_state(TASK_RUNNING);
 515
 516 out:
 517         spin_unlock_irqrestore(fence->lock, flags);
 518         return ret;
 519 }
 520 EXPORT_SYMBOL(dma_fence_default_wait);
 521
 522 static bool
 523 dma_fence_test_signaled_any(struct dma_fence **fences, uint32_t count,
 524                             uint32_t *idx)
 525 {
 526         int i;
 527
 528         for (i = 0; i < count; ++i) {
 529                 struct dma_fence *fence = fences[i];
 530                 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
 531                         if (idx)
 532                                 *idx = i;
 533                         return true;
 534                 }
 535         }
 536         return false;
 537 }
 538
 539 /**
 540  * dma_fence_wait_any_timeout - sleep until any fence gets signaled
 541  * or until timeout elapses
 542  * @fences: array of fences to wait on
 543  * @count: number of fences to wait on
 544  * @intr: if true, do an interruptible wait
 545  * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
 546  * @idx: used to store the first signaled fence index, meaningful only on
 547  *      positive return
 548  *
 549  * Returns -EINVAL on custom fence wait implementation, -ERESTARTSYS if
 550  * interrupted, 0 if the wait timed out, or the remaining timeout in jiffies
 551  * on success.
 552  *
 553  * Synchronous waits for the first fence in the array to be signaled. The
 554  * caller needs to hold a reference to all fences in the array, otherwise a
 555  * fence might be freed before return, resulting in undefined behavior.
 556  *
 557  * See also dma_fence_wait() and dma_fence_wait_timeout().
 558  */
 559 signed long
 560 dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count,
 561                            bool intr, signed long timeout, uint32_t *idx)
 562 {
 563         struct default_wait_cb *cb;
 564         signed long ret = timeout;
 565         unsigned i;
 566
 567         if (WARN_ON(!fences || !count || timeout < 0))
 568                 return -EINVAL;
 569
 570         if (timeout == 0) {
 571                 for (i = 0; i < count; ++i)
 572                         if (dma_fence_is_signaled(fences[i])) {
 573                                 if (idx)
 574                                         *idx = i;
 575                                 return 1;
 576                         }
 577
 578                 return 0;
 579         }
 580
 581         cb = kcalloc(count, sizeof(struct default_wait_cb), GFP_KERNEL);
 582         if (cb == NULL) {
 583                 ret = -ENOMEM;
 584                 goto err_free_cb;
 585         }
 586
 587         for (i = 0; i < count; ++i) {
 588                 struct dma_fence *fence = fences[i];
 589
 590                 cb[i].task = current;
 591                 if (dma_fence_add_callback(fence, &cb[i].base,
 592                                            dma_fence_default_wait_cb)) {
 593                         /* This fence is already signaled */
 594                         if (idx)
 595                                 *idx = i;
 596                         goto fence_rm_cb;
 597                 }
 598         }
 599
 600         while (ret > 0) {
 601                 if (intr)
 602                         set_current_state(TASK_INTERRUPTIBLE);
 603                 else
 604                         set_current_state(TASK_UNINTERRUPTIBLE);
 605
 606                 if (dma_fence_test_signaled_any(fences, count, idx))
 607                         break;
 608
 609                 ret = schedule_timeout(ret);
 610
 611                 if (ret > 0 && intr && signal_pending(current))
 612                         ret = -ERESTARTSYS;
 613         }
 614
 615         __set_current_state(TASK_RUNNING);
 616
 617 fence_rm_cb:
 618         while (i-- > 0)
 619                 dma_fence_remove_callback(fences[i], &cb[i].base);
 620
 621 err_free_cb:
 622         kfree(cb);
 623
 624         return ret;
 625 }
 626 EXPORT_SYMBOL(dma_fence_wait_any_timeout);
 627
 628 /**
 629  * dma_fence_init - Initialize a custom fence.
 630  * @fence: the fence to initialize
 631  * @ops: the dma_fence_ops for operations on this fence
 632  * @lock: the irqsafe spinlock to use for locking this fence
 633  * @context: the execution context this fence is run on
 634  * @seqno: a linear increasing sequence number for this context
 635  *
 636  * Initializes an allocated fence, the caller doesn't have to keep its
 637  * refcount after committing with this fence, but it will need to hold a
 638  * refcount again if &dma_fence_ops.enable_signaling gets called.
 639  *
 640  * context and seqno are used for easy comparison between fences, allowing
 641  * to check which fence is later by simply using dma_fence_later().
 642  */
 643 void
 644 dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
 645                spinlock_t *lock, u64 context, u64 seqno)
 646 {
 647         BUG_ON(!lock);
 648         BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name);
 649
 650         kref_init(&fence->refcount);
 651         fence->ops = ops;
 652         INIT_LIST_HEAD(&fence->cb_list);
 653         fence->lock = lock;
 654         fence->context = context;
 655         fence->seqno = seqno;
 656         fence->flags = 0UL;
 657         fence->error = 0;
 658
 659         trace_dma_fence_init(fence);
 660 }
 661 EXPORT_SYMBOL(dma_fence_init);