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 dma_resv 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         struct list_head cb_list;
 133
 134         lockdep_assert_held(fence->lock);
 135
 136         if (unlikely(test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
 137                                       &fence->flags)))
 138                 return -EINVAL;
 139
 140         /* Stash the cb_list before replacing it with the timestamp */
 141         list_replace(&fence->cb_list, &cb_list);
 142
 143         fence->timestamp = ktime_get();
 144         set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
 145         trace_dma_fence_signaled(fence);
 146
 147         list_for_each_entry_safe(cur, tmp, &cb_list, node) {
 148                 INIT_LIST_HEAD(&cur->node);
 149                 cur->func(fence, cur);
 150         }
 151
 152         return 0;
 153 }
 154 EXPORT_SYMBOL(dma_fence_signal_locked);
 155
 156 /**
 157  * dma_fence_signal - signal completion of a fence
 158  * @fence: the fence to signal
 159  *
 160  * Signal completion for software callbacks on a fence, this will unblock
 161  * dma_fence_wait() calls and run all the callbacks added with
 162  * dma_fence_add_callback(). Can be called multiple times, but since a fence
 163  * can only go from the unsignaled to the signaled state and not back, it will
 164  * only be effective the first time.
 165  *
 166  * Returns 0 on success and a negative error value when @fence has been
 167  * signalled already.
 168  */
 169 int dma_fence_signal(struct dma_fence *fence)
 170 {
 171         unsigned long flags;
 172         int ret;
 173
 174         if (!fence)
 175                 return -EINVAL;
 176
 177         spin_lock_irqsave(fence->lock, flags);
 178         ret = dma_fence_signal_locked(fence);
 179         spin_unlock_irqrestore(fence->lock, flags);
 180
 181         return ret;
 182 }
 183 EXPORT_SYMBOL(dma_fence_signal);
 184
 185 /**
 186  * dma_fence_wait_timeout - sleep until the fence gets signaled
 187  * or until timeout elapses
 188  * @fence: the fence to wait on
 189  * @intr: if true, do an interruptible wait
 190  * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
 191  *
 192  * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
 193  * remaining timeout in jiffies on success. Other error values may be
 194  * returned on custom implementations.
 195  *
 196  * Performs a synchronous wait on this fence. It is assumed the caller
 197  * directly or indirectly (buf-mgr between reservation and committing)
 198  * holds a reference to the fence, otherwise the fence might be
 199  * freed before return, resulting in undefined behavior.
 200  *
 201  * See also dma_fence_wait() and dma_fence_wait_any_timeout().
 202  */
 203 signed long
 204 dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
 205 {
 206         signed long ret;
 207
 208         if (WARN_ON(timeout < 0))
 209                 return -EINVAL;
 210
 211         trace_dma_fence_wait_start(fence);
 212         if (fence->ops->wait)
 213                 ret = fence->ops->wait(fence, intr, timeout);
 214         else
 215                 ret = dma_fence_default_wait(fence, intr, timeout);
 216         trace_dma_fence_wait_end(fence);
 217         return ret;
 218 }
 219 EXPORT_SYMBOL(dma_fence_wait_timeout);
 220
 221 /**
 222  * dma_fence_release - default relese function for fences
 223  * @kref: &dma_fence.recfount
 224  *
 225  * This is the default release functions for &dma_fence. Drivers shouldn't call
 226  * this directly, but instead call dma_fence_put().
 227  */
 228 void dma_fence_release(struct kref *kref)
 229 {
 230         struct dma_fence *fence =
 231                 container_of(kref, struct dma_fence, refcount);
 232
 233         trace_dma_fence_destroy(fence);
 234
 235         if (WARN(!list_empty(&fence->cb_list) &&
 236                  !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags),
 237                  "Fence %s:%s:%llx:%llx released with pending signals!\n",
 238                  fence->ops->get_driver_name(fence),
 239                  fence->ops->get_timeline_name(fence),
 240                  fence->context, fence->seqno)) {
 241                 unsigned long flags;
 242
 243                 /*
 244                  * Failed to signal before release, likely a refcounting issue.
 245                  *
 246                  * This should never happen, but if it does make sure that we
 247                  * don't leave chains dangling. We set the error flag first
 248                  * so that the callbacks know this signal is due to an error.
 249                  */
 250                 spin_lock_irqsave(fence->lock, flags);
 251                 fence->error = -EDEADLK;
 252                 dma_fence_signal_locked(fence);
 253                 spin_unlock_irqrestore(fence->lock, flags);
 254         }
 255
 256         if (fence->ops->release)
 257                 fence->ops->release(fence);
 258         else
 259                 dma_fence_free(fence);
 260 }
 261 EXPORT_SYMBOL(dma_fence_release);
 262
 263 /**
 264  * dma_fence_free - default release function for &dma_fence.
 265  * @fence: fence to release
 266  *
 267  * This is the default implementation for &dma_fence_ops.release. It calls
 268  * kfree_rcu() on @fence.
 269  */
 270 void dma_fence_free(struct dma_fence *fence)
 271 {
 272         kfree_rcu(fence, rcu);
 273 }
 274 EXPORT_SYMBOL(dma_fence_free);
 275
 276 /**
 277  * dma_fence_enable_sw_signaling - enable signaling on fence
 278  * @fence: the fence to enable
 279  *
 280  * This will request for sw signaling to be enabled, to make the fence
 281  * complete as soon as possible. This calls &dma_fence_ops.enable_signaling
 282  * internally.
 283  */
 284 void dma_fence_enable_sw_signaling(struct dma_fence *fence)
 285 {
 286         unsigned long flags;
 287
 288         if (!test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
 289                               &fence->flags) &&
 290             !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
 291             fence->ops->enable_signaling) {
 292                 trace_dma_fence_enable_signal(fence);
 293
 294                 spin_lock_irqsave(fence->lock, flags);
 295
 296                 if (!fence->ops->enable_signaling(fence))
 297                         dma_fence_signal_locked(fence);
 298
 299                 spin_unlock_irqrestore(fence->lock, flags);
 300         }
 301 }
 302 EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
 303
 304 /**
 305  * dma_fence_add_callback - add a callback to be called when the fence
 306  * is signaled
 307  * @fence: the fence to wait on
 308  * @cb: the callback to register
 309  * @func: the function to call
 310  *
 311  * @cb will be initialized by dma_fence_add_callback(), no initialization
 312  * by the caller is required. Any number of callbacks can be registered
 313  * to a fence, but a callback can only be registered to one fence at a time.
 314  *
 315  * Note that the callback can be called from an atomic context.  If
 316  * fence is already signaled, this function will return -ENOENT (and
 317  * *not* call the callback).
 318  *
 319  * Add a software callback to the fence. Same restrictions apply to
 320  * refcount as it does to dma_fence_wait(), however the caller doesn't need to
 321  * keep a refcount to fence afterward dma_fence_add_callback() has returned:
 322  * when software access is enabled, the creator of the fence is required to keep
 323  * the fence alive until after it signals with dma_fence_signal(). The callback
 324  * itself can be called from irq context.
 325  *
 326  * Returns 0 in case of success, -ENOENT if the fence is already signaled
 327  * and -EINVAL in case of error.
 328  */
 329 int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
 330                            dma_fence_func_t func)
 331 {
 332         unsigned long flags;
 333         int ret = 0;
 334         bool was_set;
 335
 336         if (WARN_ON(!fence || !func))
 337                 return -EINVAL;
 338
 339         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
 340                 INIT_LIST_HEAD(&cb->node);
 341                 return -ENOENT;
 342         }
 343
 344         spin_lock_irqsave(fence->lock, flags);
 345
 346         was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
 347                                    &fence->flags);
 348
 349         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 350                 ret = -ENOENT;
 351         else if (!was_set && fence->ops->enable_signaling) {
 352                 trace_dma_fence_enable_signal(fence);
 353
 354                 if (!fence->ops->enable_signaling(fence)) {
 355                         dma_fence_signal_locked(fence);
 356                         ret = -ENOENT;
 357                 }
 358         }
 359
 360         if (!ret) {
 361                 cb->func = func;
 362                 list_add_tail(&cb->node, &fence->cb_list);
 363         } else
 364                 INIT_LIST_HEAD(&cb->node);
 365         spin_unlock_irqrestore(fence->lock, flags);
 366
 367         return ret;
 368 }
 369 EXPORT_SYMBOL(dma_fence_add_callback);
 370
 371 /**
 372  * dma_fence_get_status - returns the status upon completion
 373  * @fence: the dma_fence to query
 374  *
 375  * This wraps dma_fence_get_status_locked() to return the error status
 376  * condition on a signaled fence. See dma_fence_get_status_locked() for more
 377  * details.
 378  *
 379  * Returns 0 if the fence has not yet been signaled, 1 if the fence has
 380  * been signaled without an error condition, or a negative error code
 381  * if the fence has been completed in err.
 382  */
 383 int dma_fence_get_status(struct dma_fence *fence)
 384 {
 385         unsigned long flags;
 386         int status;
 387
 388         spin_lock_irqsave(fence->lock, flags);
 389         status = dma_fence_get_status_locked(fence);
 390         spin_unlock_irqrestore(fence->lock, flags);
 391
 392         return status;
 393 }
 394 EXPORT_SYMBOL(dma_fence_get_status);
 395
 396 /**
 397  * dma_fence_remove_callback - remove a callback from the signaling list
 398  * @fence: the fence to wait on
 399  * @cb: the callback to remove
 400  *
 401  * Remove a previously queued callback from the fence. This function returns
 402  * true if the callback is successfully removed, or false if the fence has
 403  * already been signaled.
 404  *
 405  * *WARNING*:
 406  * Cancelling a callback should only be done if you really know what you're
 407  * doing, since deadlocks and race conditions could occur all too easily. For
 408  * this reason, it should only ever be done on hardware lockup recovery,
 409  * with a reference held to the fence.
 410  *
 411  * Behaviour is undefined if @cb has not been added to @fence using
 412  * dma_fence_add_callback() beforehand.
 413  */
 414 bool
 415 dma_fence_remove_callback(struct dma_fence *fence, struct dma_fence_cb *cb)
 416 {
 417         unsigned long flags;
 418         bool ret;
 419
 420         spin_lock_irqsave(fence->lock, flags);
 421
 422         ret = !list_empty(&cb->node);
 423         if (ret)
 424                 list_del_init(&cb->node);
 425
 426         spin_unlock_irqrestore(fence->lock, flags);
 427
 428         return ret;
 429 }
 430 EXPORT_SYMBOL(dma_fence_remove_callback);
 431
 432 struct default_wait_cb {
 433         struct dma_fence_cb base;
 434         struct task_struct *task;
 435 };
 436
 437 static void
 438 dma_fence_default_wait_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
 439 {
 440         struct default_wait_cb *wait =
 441                 container_of(cb, struct default_wait_cb, base);
 442
 443         wake_up_state(wait->task, TASK_NORMAL);
 444 }
 445
 446 /**
 447  * dma_fence_default_wait - default sleep until the fence gets signaled
 448  * or until timeout elapses
 449  * @fence: the fence to wait on
 450  * @intr: if true, do an interruptible wait
 451  * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
 452  *
 453  * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or the
 454  * remaining timeout in jiffies on success. If timeout is zero the value one is
 455  * returned if the fence is already signaled for consistency with other
 456  * functions taking a jiffies timeout.
 457  */
 458 signed long
 459 dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
 460 {
 461         struct default_wait_cb cb;
 462         unsigned long flags;
 463         signed long ret = timeout ? timeout : 1;
 464         bool was_set;
 465
 466         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 467                 return ret;
 468
 469         spin_lock_irqsave(fence->lock, flags);
 470
 471         if (intr && signal_pending(current)) {
 472                 ret = -ERESTARTSYS;
 473                 goto out;
 474         }
 475
 476         was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
 477                                    &fence->flags);
 478
 479         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 480                 goto out;
 481
 482         if (!was_set && fence->ops->enable_signaling) {
 483                 trace_dma_fence_enable_signal(fence);
 484
 485                 if (!fence->ops->enable_signaling(fence)) {
 486                         dma_fence_signal_locked(fence);
 487                         goto out;
 488                 }
 489         }
 490
 491         if (!timeout) {
 492                 ret = 0;
 493                 goto out;
 494         }
 495
 496         cb.base.func = dma_fence_default_wait_cb;
 497         cb.task = current;
 498         list_add(&cb.base.node, &fence->cb_list);
 499
 500         while (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) && ret > 0) {
 501                 if (intr)
 502                         __set_current_state(TASK_INTERRUPTIBLE);
 503                 else
 504                         __set_current_state(TASK_UNINTERRUPTIBLE);
 505                 spin_unlock_irqrestore(fence->lock, flags);
 506
 507                 ret = schedule_timeout(ret);
 508
 509                 spin_lock_irqsave(fence->lock, flags);
 510                 if (ret > 0 && intr && signal_pending(current))
 511                         ret = -ERESTARTSYS;
 512         }
 513
 514         if (!list_empty(&cb.base.node))
 515                 list_del(&cb.base.node);
 516         __set_current_state(TASK_RUNNING);
 517
 518 out:
 519         spin_unlock_irqrestore(fence->lock, flags);
 520         return ret;
 521 }
 522 EXPORT_SYMBOL(dma_fence_default_wait);
 523
 524 static bool
 525 dma_fence_test_signaled_any(struct dma_fence **fences, uint32_t count,
 526                             uint32_t *idx)
 527 {
 528         int i;
 529
 530         for (i = 0; i < count; ++i) {
 531                 struct dma_fence *fence = fences[i];
 532                 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
 533                         if (idx)
 534                                 *idx = i;
 535                         return true;
 536                 }
 537         }
 538         return false;
 539 }
 540
 541 /**
 542  * dma_fence_wait_any_timeout - sleep until any fence gets signaled
 543  * or until timeout elapses
 544  * @fences: array of fences to wait on
 545  * @count: number of fences to wait on
 546  * @intr: if true, do an interruptible wait
 547  * @timeout: timeout value in jiffies, or MAX_SCHEDULE_TIMEOUT
 548  * @idx: used to store the first signaled fence index, meaningful only on
 549  *      positive return
 550  *
 551  * Returns -EINVAL on custom fence wait implementation, -ERESTARTSYS if
 552  * interrupted, 0 if the wait timed out, or the remaining timeout in jiffies
 553  * on success.
 554  *
 555  * Synchronous waits for the first fence in the array to be signaled. The
 556  * caller needs to hold a reference to all fences in the array, otherwise a
 557  * fence might be freed before return, resulting in undefined behavior.
 558  *
 559  * See also dma_fence_wait() and dma_fence_wait_timeout().
 560  */
 561 signed long
 562 dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count,
 563                            bool intr, signed long timeout, uint32_t *idx)
 564 {
 565         struct default_wait_cb *cb;
 566         signed long ret = timeout;
 567         unsigned i;
 568
 569         if (WARN_ON(!fences || !count || timeout < 0))
 570                 return -EINVAL;
 571
 572         if (timeout == 0) {
 573                 for (i = 0; i < count; ++i)
 574                         if (dma_fence_is_signaled(fences[i])) {
 575                                 if (idx)
 576                                         *idx = i;
 577                                 return 1;
 578                         }
 579
 580                 return 0;
 581         }
 582
 583         cb = kcalloc(count, sizeof(struct default_wait_cb), GFP_KERNEL);
 584         if (cb == NULL) {
 585                 ret = -ENOMEM;
 586                 goto err_free_cb;
 587         }
 588
 589         for (i = 0; i < count; ++i) {
 590                 struct dma_fence *fence = fences[i];
 591
 592                 cb[i].task = current;
 593                 if (dma_fence_add_callback(fence, &cb[i].base,
 594                                            dma_fence_default_wait_cb)) {
 595                         /* This fence is already signaled */
 596                         if (idx)
 597                                 *idx = i;
 598                         goto fence_rm_cb;
 599                 }
 600         }
 601
 602         while (ret > 0) {
 603                 if (intr)
 604                         set_current_state(TASK_INTERRUPTIBLE);
 605                 else
 606                         set_current_state(TASK_UNINTERRUPTIBLE);
 607
 608                 if (dma_fence_test_signaled_any(fences, count, idx))
 609                         break;
 610
 611                 ret = schedule_timeout(ret);
 612
 613                 if (ret > 0 && intr && signal_pending(current))
 614                         ret = -ERESTARTSYS;
 615         }
 616
 617         __set_current_state(TASK_RUNNING);
 618
 619 fence_rm_cb:
 620         while (i-- > 0)
 621                 dma_fence_remove_callback(fences[i], &cb[i].base);
 622
 623 err_free_cb:
 624         kfree(cb);
 625
 626         return ret;
 627 }
 628 EXPORT_SYMBOL(dma_fence_wait_any_timeout);
 629
 630 /**
 631  * dma_fence_init - Initialize a custom fence.
 632  * @fence: the fence to initialize
 633  * @ops: the dma_fence_ops for operations on this fence
 634  * @lock: the irqsafe spinlock to use for locking this fence
 635  * @context: the execution context this fence is run on
 636  * @seqno: a linear increasing sequence number for this context
 637  *
 638  * Initializes an allocated fence, the caller doesn't have to keep its
 639  * refcount after committing with this fence, but it will need to hold a
 640  * refcount again if &dma_fence_ops.enable_signaling gets called.
 641  *
 642  * context and seqno are used for easy comparison between fences, allowing
 643  * to check which fence is later by simply using dma_fence_later().
 644  */
 645 void
 646 dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
 647                spinlock_t *lock, u64 context, u64 seqno)
 648 {
 649         BUG_ON(!lock);
 650         BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name);
 651
 652         kref_init(&fence->refcount);
 653         fence->ops = ops;
 654         INIT_LIST_HEAD(&fence->cb_list);
 655         fence->lock = lock;
 656         fence->context = context;
 657         fence->seqno = seqno;
 658         fence->flags = 0UL;
 659         fence->error = 0;
 660
 661         trace_dma_fence_init(fence);
 662 }
 663 EXPORT_SYMBOL(dma_fence_init);