1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3 * Fence mechanism for dma-buf 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 #ifndef __LINUX_DMA_FENCE_H
14 #define __LINUX_DMA_FENCE_H
15
16 #include <linux/err.h>
17 #include <linux/wait.h>
18 #include <linux/list.h>
19 #include <linux/bitops.h>
20 #include <linux/kref.h>
21 #include <linux/sched.h>
22 #include <linux/printk.h>
23 #include <linux/rcupdate.h>
24 #include <linux/timekeeping.h>
25
26 struct dma_fence;
27 struct dma_fence_ops;
28 struct dma_fence_cb;
29
30 /**
31 * struct dma_fence - software synchronization primitive
32 * @refcount: refcount for this fence
33 * @ops: dma_fence_ops associated with this fence
34 * @rcu: used for releasing fence with kfree_rcu
35 * @cb_list: list of all callbacks to call
36 * @lock: spin_lock_irqsave used for locking
37 * @context: execution context this fence belongs to, returned by
38 * dma_fence_context_alloc()
39 * @seqno: the sequence number of this fence inside the execution context,
40 * can be compared to decide which fence would be signaled later.
41 * @flags: A mask of DMA_FENCE_FLAG_* defined below
42 * @timestamp: Timestamp when the fence was signaled.
43 * @error: Optional, only valid if < 0, must be set before calling
44 * dma_fence_signal, indicates that the fence has completed with an error.
45 *
46 * the flags member must be manipulated and read using the appropriate
47 * atomic ops (bit_*), so taking the spinlock will not be needed most
48 * of the time.
49 *
50 * DMA_FENCE_FLAG_SIGNALED_BIT - fence is already signaled
51 * DMA_FENCE_FLAG_TIMESTAMP_BIT - timestamp recorded for fence signaling
52 * DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called
53 * DMA_FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
54 * implementer of the fence for its own purposes. Can be used in different
55 * ways by different fence implementers, so do not rely on this.
56 *
57 * Since atomic bitops are used, this is not guaranteed to be the case.
58 * Particularly, if the bit was set, but dma_fence_signal was called right
59 * before this bit was set, it would have been able to set the
60 * DMA_FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
61 * Adding a check for DMA_FENCE_FLAG_SIGNALED_BIT after setting
62 * DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
63 * after dma_fence_signal was called, any enable_signaling call will have either
64 * been completed, or never called at all.
65 */
66 struct dma_fence {
67 spinlock_t *lock;
68 const struct dma_fence_ops *ops;
69 /*
70 * We clear the callback list on kref_put so that by the time we
71 * release the fence it is unused. No one should be adding to the
72 * cb_list that they don't themselves hold a reference for.
73 *
74 * The lifetime of the timestamp is similarly tied to both the
75 * rcu freelist and the cb_list. The timestamp is only set upon
76 * signaling while simultaneously notifying the cb_list. Ergo, we
77 * only use either the cb_list of timestamp. Upon destruction,
78 * neither are accessible, and so we can use the rcu. This means
79 * that the cb_list is *only* valid until the signal bit is set,
80 * and to read either you *must* hold a reference to the fence,
81 * and not just the rcu_read_lock.
82 *
83 * Listed in chronological order.
84 */
85 union {
86 struct list_head cb_list;
87 /* @cb_list replaced by @timestamp on dma_fence_signal() */
88 ktime_t timestamp;
89 /* @timestamp replaced by @rcu on dma_fence_release() */
90 struct rcu_head rcu;
91 };
92 u64 context;
93 u64 seqno;
94 unsigned long flags;
95 struct kref refcount;
96 int error;
97 };
98
99 enum dma_fence_flag_bits {
100 DMA_FENCE_FLAG_SIGNALED_BIT,
101 DMA_FENCE_FLAG_TIMESTAMP_BIT,
102 DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
103 DMA_FENCE_FLAG_USER_BITS, /* must always be last member */
104 };
105
106 typedef void (*dma_fence_func_t)(struct dma_fence *fence,
107 struct dma_fence_cb *cb);
108
109 /**
110 * struct dma_fence_cb - callback for dma_fence_add_callback()
111 * @node: used by dma_fence_add_callback() to append this struct to fence::cb_list
112 * @func: dma_fence_func_t to call
113 *
114 * This struct will be initialized by dma_fence_add_callback(), additional
115 * data can be passed along by embedding dma_fence_cb in another struct.
116 */
117 struct dma_fence_cb {
118 struct list_head node;
119 dma_fence_func_t func;
120 };
121
122 /**
123 * struct dma_fence_ops - operations implemented for fence
124 *
125 */
126 struct dma_fence_ops {
127 /**
128 * @use_64bit_seqno:
129 *
130 * True if this dma_fence implementation uses 64bit seqno, false
131 * otherwise.
132 */
133 bool use_64bit_seqno;
134
135 /**
136 * @get_driver_name:
137 *
138 * Returns the driver name. This is a callback to allow drivers to
139 * compute the name at runtime, without having it to store permanently
140 * for each fence, or build a cache of some sort.
141 *
142 * This callback is mandatory.
143 */
144 const char * (*get_driver_name)(struct dma_fence *fence);
145
146 /**
147 * @get_timeline_name:
148 *
149 * Return the name of the context this fence belongs to. This is a
150 * callback to allow drivers to compute the name at runtime, without
151 * having it to store permanently for each fence, or build a cache of
152 * some sort.
153 *
154 * This callback is mandatory.
155 */
156 const char * (*get_timeline_name)(struct dma_fence *fence);
157
158 /**
159 * @enable_signaling:
160 *
161 * Enable software signaling of fence.
162 *
163 * For fence implementations that have the capability for hw->hw
164 * signaling, they can implement this op to enable the necessary
165 * interrupts, or insert commands into cmdstream, etc, to avoid these
166 * costly operations for the common case where only hw->hw
167 * synchronization is required. This is called in the first
168 * dma_fence_wait() or dma_fence_add_callback() path to let the fence
169 * implementation know that there is another driver waiting on the
170 * signal (ie. hw->sw case).
171 *
172 * This function can be called from atomic context, but not
173 * from irq context, so normal spinlocks can be used.
174 *
175 * A return value of false indicates the fence already passed,
176 * or some failure occurred that made it impossible to enable
177 * signaling. True indicates successful enabling.
178 *
179 * &dma_fence.error may be set in enable_signaling, but only when false
180 * is returned.
181 *
182 * Since many implementations can call dma_fence_signal() even when before
183 * @enable_signaling has been called there's a race window, where the
184 * dma_fence_signal() might result in the final fence reference being
185 * released and its memory freed. To avoid this, implementations of this
186 * callback should grab their own reference using dma_fence_get(), to be
187 * released when the fence is signalled (through e.g. the interrupt
188 * handler).
189 *
190 * This callback is optional. If this callback is not present, then the
191 * driver must always have signaling enabled.
192 */
193 bool (*enable_signaling)(struct dma_fence *fence);
194
195 /**
196 * @signaled:
197 *
198 * Peek whether the fence is signaled, as a fastpath optimization for
199 * e.g. dma_fence_wait() or dma_fence_add_callback(). Note that this
200 * callback does not need to make any guarantees beyond that a fence
201 * once indicates as signalled must always return true from this
202 * callback. This callback may return false even if the fence has
203 * completed already, in this case information hasn't propogated throug
204 * the system yet. See also dma_fence_is_signaled().
205 *
206 * May set &dma_fence.error if returning true.
207 *
208 * This callback is optional.
209 */
210 bool (*signaled)(struct dma_fence *fence);
211
212 /**
213 * @wait:
214 *
215 * Custom wait implementation, defaults to dma_fence_default_wait() if
216 * not set.
217 *
218 * Deprecated and should not be used by new implementations. Only used
219 * by existing implementations which need special handling for their
220 * hardware reset procedure.
221 *
222 * Must return -ERESTARTSYS if the wait is intr = true and the wait was
223 * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
224 * timed out. Can also return other error values on custom implementations,
225 * which should be treated as if the fence is signaled. For example a hardware
226 * lockup could be reported like that.
227 */
228 signed long (*wait)(struct dma_fence *fence,
229 bool intr, signed long timeout);
230
231 /**
232 * @release:
233 *
234 * Called on destruction of fence to release additional resources.
235 * Can be called from irq context. This callback is optional. If it is
236 * NULL, then dma_fence_free() is instead called as the default
237 * implementation.
238 */
239 void (*release)(struct dma_fence *fence);
240
241 /**
242 * @fence_value_str:
243 *
244 * Callback to fill in free-form debug info specific to this fence, like
245 * the sequence number.
246 *
247 * This callback is optional.
248 */
249 void (*fence_value_str)(struct dma_fence *fence, char *str, int size);
250
251 /**
252 * @timeline_value_str:
253 *
254 * Fills in the current value of the timeline as a string, like the
255 * sequence number. Note that the specific fence passed to this function
256 * should not matter, drivers should only use it to look up the
257 * corresponding timeline structures.
258 */
259 void (*timeline_value_str)(struct dma_fence *fence,
260 char *str, int size);
261
262 /**
263 * @set_deadline:
264 *
265 * Callback to allow a fence waiter to inform the fence signaler of
266 * an upcoming deadline, such as vblank, by which point the waiter
267 * would prefer the fence to be signaled by. This is intended to
268 * give feedback to the fence signaler to aid in power management
269 * decisions, such as boosting GPU frequency.
270 *
271 * This is called without &dma_fence.lock held, it can be called
272 * multiple times and from any context. Locking is up to the callee
273 * if it has some state to manage. If multiple deadlines are set,
274 * the expectation is to track the soonest one. If the deadline is
275 * before the current time, it should be interpreted as an immediate
276 * deadline.
277 *
278 * This callback is optional.
279 */
280 void (*set_deadline)(struct dma_fence *fence, ktime_t deadline);
281 };
282
283 void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
284 spinlock_t *lock, u64 context, u64 seqno);
285
286 void dma_fence_release(struct kref *kref);
287 void dma_fence_free(struct dma_fence *fence);
288 void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq);
289
290 /**
291 * dma_fence_put - decreases refcount of the fence
292 * @fence: fence to reduce refcount of
293 */
294 static inline void dma_fence_put(struct dma_fence *fence)
295 {
296 if (fence)
297 kref_put(&fence->refcount, dma_fence_release);
298 }
299
300 /**
301 * dma_fence_get - increases refcount of the fence
302 * @fence: fence to increase refcount of
303 *
304 * Returns the same fence, with refcount increased by 1.
305 */
306 static inline struct dma_fence *dma_fence_get(struct dma_fence *fence)
307 {
308 if (fence)
309 kref_get(&fence->refcount);
310 return fence;
311 }
312
313 /**
314 * dma_fence_get_rcu - get a fence from a dma_resv_list with
315 * rcu read lock
316 * @fence: fence to increase refcount of
317 *
318 * Function returns NULL if no refcount could be obtained, or the fence.
319 */
320 static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence)
321 {
322 if (kref_get_unless_zero(&fence->refcount))
323 return fence;
324 else
325 return NULL;
326 }
327
328 /**
329 * dma_fence_get_rcu_safe - acquire a reference to an RCU tracked fence
330 * @fencep: pointer to fence to increase refcount of
331 *
332 * Function returns NULL if no refcount could be obtained, or the fence.
333 * This function handles acquiring a reference to a fence that may be
334 * reallocated within the RCU grace period (such as with SLAB_TYPESAFE_BY_RCU),
335 * so long as the caller is using RCU on the pointer to the fence.
336 *
337 * An alternative mechanism is to employ a seqlock to protect a bunch of
338 * fences, such as used by struct dma_resv. When using a seqlock,
339 * the seqlock must be taken before and checked after a reference to the
340 * fence is acquired (as shown here).
341 *
342 * The caller is required to hold the RCU read lock.
343 */
344 static inline struct dma_fence *
345 dma_fence_get_rcu_safe(struct dma_fence __rcu **fencep)
346 {
347 do {
348 struct dma_fence *fence;
349
350 fence = rcu_dereference(*fencep);
351 if (!fence)
352 return NULL;
353
354 if (!dma_fence_get_rcu(fence))
355 continue;
356
357 /* The atomic_inc_not_zero() inside dma_fence_get_rcu()
358 * provides a full memory barrier upon success (such as now).
359 * This is paired with the write barrier from assigning
360 * to the __rcu protected fence pointer so that if that
361 * pointer still matches the current fence, we know we
362 * have successfully acquire a reference to it. If it no
363 * longer matches, we are holding a reference to some other
364 * reallocated pointer. This is possible if the allocator
365 * is using a freelist like SLAB_TYPESAFE_BY_RCU where the
366 * fence remains valid for the RCU grace period, but it
367 * may be reallocated. When using such allocators, we are
368 * responsible for ensuring the reference we get is to
369 * the right fence, as below.
370 */
371 if (fence == rcu_access_pointer(*fencep))
372 return rcu_pointer_handoff(fence);
373
374 dma_fence_put(fence);
375 } while (1);
376 }
377
378 #ifdef CONFIG_LOCKDEP
379 bool dma_fence_begin_signalling(void);
380 void dma_fence_end_signalling(bool cookie);
381 void __dma_fence_might_wait(void);
382 #else
383 static inline bool dma_fence_begin_signalling(void)
384 {
385 return true;
386 }
387 static inline void dma_fence_end_signalling(bool cookie) {}
388 static inline void __dma_fence_might_wait(void) {}
389 #endif
390
391 int dma_fence_signal(struct dma_fence *fence);
392 int dma_fence_signal_locked(struct dma_fence *fence);
393 int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
394 int dma_fence_signal_timestamp_locked(struct dma_fence *fence,
395 ktime_t timestamp);
396 signed long dma_fence_default_wait(struct dma_fence *fence,
397 bool intr, signed long timeout);
398 int dma_fence_add_callback(struct dma_fence *fence,
399 struct dma_fence_cb *cb,
400 dma_fence_func_t func);
401 bool dma_fence_remove_callback(struct dma_fence *fence,
402 struct dma_fence_cb *cb);
403 void dma_fence_enable_sw_signaling(struct dma_fence *fence);
404
405 /**
406 * dma_fence_is_signaled_locked - Return an indication if the fence
407 * is signaled yet.
408 * @fence: the fence to check
409 *
410 * Returns true if the fence was already signaled, false if not. Since this
411 * function doesn't enable signaling, it is not guaranteed to ever return
412 * true if dma_fence_add_callback(), dma_fence_wait() or
413 * dma_fence_enable_sw_signaling() haven't been called before.
414 *
415 * This function requires &dma_fence.lock to be held.
416 *
417 * See also dma_fence_is_signaled().
418 */
419 static inline bool
420 dma_fence_is_signaled_locked(struct dma_fence *fence)
421 {
422 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
423 return true;
424
425 if (fence->ops->signaled && fence->ops->signaled(fence)) {
426 dma_fence_signal_locked(fence);
427 return true;
428 }
429
430 return false;
431 }
432
433 /**
434 * dma_fence_is_signaled - Return an indication if the fence is signaled yet.
435 * @fence: the fence to check
436 *
437 * Returns true if the fence was already signaled, false if not. Since this
438 * function doesn't enable signaling, it is not guaranteed to ever return
439 * true if dma_fence_add_callback(), dma_fence_wait() or
440 * dma_fence_enable_sw_signaling() haven't been called before.
441 *
442 * It's recommended for seqno fences to call dma_fence_signal when the
443 * operation is complete, it makes it possible to prevent issues from
444 * wraparound between time of issue and time of use by checking the return
445 * value of this function before calling hardware-specific wait instructions.
446 *
447 * See also dma_fence_is_signaled_locked().
448 */
449 static inline bool
450 dma_fence_is_signaled(struct dma_fence *fence)
451 {
452 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
453 return true;
454
455 if (fence->ops->signaled && fence->ops->signaled(fence)) {
456 dma_fence_signal(fence);
457 return true;
458 }
459
460 return false;
461 }
462
463 /**
464 * __dma_fence_is_later - return if f1 is chronologically later than f2
465 * @f1: the first fence's seqno
466 * @f2: the second fence's seqno from the same context
467 * @ops: dma_fence_ops associated with the seqno
468 *
469 * Returns true if f1 is chronologically later than f2. Both fences must be
470 * from the same context, since a seqno is not common across contexts.
471 */
472 static inline bool __dma_fence_is_later(u64 f1, u64 f2,
473 const struct dma_fence_ops *ops)
474 {
475 /* This is for backward compatibility with drivers which can only handle
476 * 32bit sequence numbers. Use a 64bit compare when the driver says to
477 * do so.
478 */
479 if (ops->use_64bit_seqno)
480 return f1 > f2;
481
482 return (int)(lower_32_bits(f1) - lower_32_bits(f2)) > 0;
483 }
484
485 /**
486 * dma_fence_is_later - return if f1 is chronologically later than f2
487 * @f1: the first fence from the same context
488 * @f2: the second fence from the same context
489 *
490 * Returns true if f1 is chronologically later than f2. Both fences must be
491 * from the same context, since a seqno is not re-used across contexts.
492 */
493 static inline bool dma_fence_is_later(struct dma_fence *f1,
494 struct dma_fence *f2)
495 {
496 if (WARN_ON(f1->context != f2->context))
497 return false;
498
499 return __dma_fence_is_later(f1->seqno, f2->seqno, f1->ops);
500 }
501
502 /**
503 * dma_fence_is_later_or_same - return true if f1 is later or same as f2
504 * @f1: the first fence from the same context
505 * @f2: the second fence from the same context
506 *
507 * Returns true if f1 is chronologically later than f2 or the same fence. Both
508 * fences must be from the same context, since a seqno is not re-used across
509 * contexts.
510 */
511 static inline bool dma_fence_is_later_or_same(struct dma_fence *f1,
512 struct dma_fence *f2)
513 {
514 return f1 == f2 || dma_fence_is_later(f1, f2);
515 }
516
517 /**
518 * dma_fence_later - return the chronologically later fence
519 * @f1: the first fence from the same context
520 * @f2: the second fence from the same context
521 *
522 * Returns NULL if both fences are signaled, otherwise the fence that would be
523 * signaled last. Both fences must be from the same context, since a seqno is
524 * not re-used across contexts.
525 */
526 static inline struct dma_fence *dma_fence_later(struct dma_fence *f1,
527 struct dma_fence *f2)
528 {
529 if (WARN_ON(f1->context != f2->context))
530 return NULL;
531
532 /*
533 * Can't check just DMA_FENCE_FLAG_SIGNALED_BIT here, it may never
534 * have been set if enable_signaling wasn't called, and enabling that
535 * here is overkill.
536 */
537 if (dma_fence_is_later(f1, f2))
538 return dma_fence_is_signaled(f1) ? NULL : f1;
539 else
540 return dma_fence_is_signaled(f2) ? NULL : f2;
541 }
542
543 /**
544 * dma_fence_get_status_locked - returns the status upon completion
545 * @fence: the dma_fence to query
546 *
547 * Drivers can supply an optional error status condition before they signal
548 * the fence (to indicate whether the fence was completed due to an error
549 * rather than success). The value of the status condition is only valid
550 * if the fence has been signaled, dma_fence_get_status_locked() first checks
551 * the signal state before reporting the error status.
552 *
553 * Returns 0 if the fence has not yet been signaled, 1 if the fence has
554 * been signaled without an error condition, or a negative error code
555 * if the fence has been completed in err.
556 */
557 static inline int dma_fence_get_status_locked(struct dma_fence *fence)
558 {
559 if (dma_fence_is_signaled_locked(fence))
560 return fence->error ?: 1;
561 else
562 return 0;
563 }
564
565 int dma_fence_get_status(struct dma_fence *fence);
566
567 /**
568 * dma_fence_set_error - flag an error condition on the fence
569 * @fence: the dma_fence
570 * @error: the error to store
571 *
572 * Drivers can supply an optional error status condition before they signal
573 * the fence, to indicate that the fence was completed due to an error
574 * rather than success. This must be set before signaling (so that the value
575 * is visible before any waiters on the signal callback are woken). This
576 * helper exists to help catching erroneous setting of #dma_fence.error.
577 */
578 static inline void dma_fence_set_error(struct dma_fence *fence,
579 int error)
580 {
581 WARN_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
582 WARN_ON(error >= 0 || error < -MAX_ERRNO);
583
584 fence->error = error;
585 }
586
587 /**
588 * dma_fence_timestamp - helper to get the completion timestamp of a fence
589 * @fence: fence to get the timestamp from.
590 *
591 * After a fence is signaled the timestamp is updated with the signaling time,
592 * but setting the timestamp can race with tasks waiting for the signaling. This
593 * helper busy waits for the correct timestamp to appear.
594 */
595 static inline ktime_t dma_fence_timestamp(struct dma_fence *fence)
596 {
597 if (WARN_ON(!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)))
598 return ktime_get();
599
600 while (!test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags))
601 cpu_relax();
602
603 return fence->timestamp;
604 }
605
606 signed long dma_fence_wait_timeout(struct dma_fence *,
607 bool intr, signed long timeout);
608 signed long dma_fence_wait_any_timeout(struct dma_fence **fences,
609 uint32_t count,
610 bool intr, signed long timeout,
611 uint32_t *idx);
612
613 /**
614 * dma_fence_wait - sleep until the fence gets signaled
615 * @fence: the fence to wait on
616 * @intr: if true, do an interruptible wait
617 *
618 * This function will return -ERESTARTSYS if interrupted by a signal,
619 * or 0 if the fence was signaled. Other error values may be
620 * returned on custom implementations.
621 *
622 * Performs a synchronous wait on this fence. It is assumed the caller
623 * directly or indirectly holds a reference to the fence, otherwise the
624 * fence might be freed before return, resulting in undefined behavior.
625 *
626 * See also dma_fence_wait_timeout() and dma_fence_wait_any_timeout().
627 */
628 static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
629 {
630 signed long ret;
631
632 /* Since dma_fence_wait_timeout cannot timeout with
633 * MAX_SCHEDULE_TIMEOUT, only valid return values are
634 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
635 */
636 ret = dma_fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
637
638 return ret < 0 ? ret : 0;
639 }
640
641 void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
642
643 struct dma_fence *dma_fence_get_stub(void);
644 struct dma_fence *dma_fence_allocate_private_stub(ktime_t timestamp);
645 u64 dma_fence_context_alloc(unsigned num);
646
647 extern const struct dma_fence_ops dma_fence_array_ops;
648 extern const struct dma_fence_ops dma_fence_chain_ops;
649
650 /**
651 * dma_fence_is_array - check if a fence is from the array subclass
652 * @fence: the fence to test
653 *
654 * Return true if it is a dma_fence_array and false otherwise.
655 */
656 static inline bool dma_fence_is_array(struct dma_fence *fence)
657 {
658 return fence->ops == &dma_fence_array_ops;
659 }
660
661 /**
662 * dma_fence_is_chain - check if a fence is from the chain subclass
663 * @fence: the fence to test
664 *
665 * Return true if it is a dma_fence_chain and false otherwise.
666 */
667 static inline bool dma_fence_is_chain(struct dma_fence *fence)
668 {
669 return fence->ops == &dma_fence_chain_ops;
670 }
671
672 /**
673 * dma_fence_is_container - check if a fence is a container for other fences
674 * @fence: the fence to test
675 *
676 * Return true if this fence is a container for other fences, false otherwise.
677 * This is important since we can't build up large fence structure or otherwise
678 * we run into recursion during operation on those fences.
679 */
680 static inline bool dma_fence_is_container(struct dma_fence *fence)
681 {
682 return dma_fence_is_array(fence) || dma_fence_is_chain(fence);
683 }
684
685 #endif /* __LINUX_DMA_FENCE_H */
686
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