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
26struct dma_fence;
27struct dma_fence_ops;
28struct 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 */
66struct 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
99enum 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
106typedef 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 */
117struct 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 */
126struct 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 is called with irq's disabled, so only spinlocks which disable
173 * IRQ's can be used in the code outside of this callback.
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 * @set_deadline:
243 *
244 * Callback to allow a fence waiter to inform the fence signaler of
245 * an upcoming deadline, such as vblank, by which point the waiter
246 * would prefer the fence to be signaled by. This is intended to
247 * give feedback to the fence signaler to aid in power management
248 * decisions, such as boosting GPU frequency.
249 *
250 * This is called without &dma_fence.lock held, it can be called
251 * multiple times and from any context. Locking is up to the callee
252 * if it has some state to manage. If multiple deadlines are set,
253 * the expectation is to track the soonest one. If the deadline is
254 * before the current time, it should be interpreted as an immediate
255 * deadline.
256 *
257 * This callback is optional.
258 */
259 void (*set_deadline)(struct dma_fence *fence, ktime_t deadline);
260};
261
262void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
263 spinlock_t *lock, u64 context, u64 seqno);
264
265void dma_fence_release(struct kref *kref);
266void dma_fence_free(struct dma_fence *fence);
267void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq);
268
269/**
270 * dma_fence_put - decreases refcount of the fence
271 * @fence: fence to reduce refcount of
272 */
273static inline void dma_fence_put(struct dma_fence *fence)
274{
275 if (fence)
276 kref_put(kref: &fence->refcount, release: dma_fence_release);
277}
278
279/**
280 * dma_fence_get - increases refcount of the fence
281 * @fence: fence to increase refcount of
282 *
283 * Returns the same fence, with refcount increased by 1.
284 */
285static inline struct dma_fence *dma_fence_get(struct dma_fence *fence)
286{
287 if (fence)
288 kref_get(kref: &fence->refcount);
289 return fence;
290}
291
292/**
293 * dma_fence_get_rcu - get a fence from a dma_resv_list with
294 * rcu read lock
295 * @fence: fence to increase refcount of
296 *
297 * Function returns NULL if no refcount could be obtained, or the fence.
298 */
299static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence)
300{
301 if (kref_get_unless_zero(kref: &fence->refcount))
302 return fence;
303 else
304 return NULL;
305}
306
307/**
308 * dma_fence_get_rcu_safe - acquire a reference to an RCU tracked fence
309 * @fencep: pointer to fence to increase refcount of
310 *
311 * Function returns NULL if no refcount could be obtained, or the fence.
312 * This function handles acquiring a reference to a fence that may be
313 * reallocated within the RCU grace period (such as with SLAB_TYPESAFE_BY_RCU),
314 * so long as the caller is using RCU on the pointer to the fence.
315 *
316 * An alternative mechanism is to employ a seqlock to protect a bunch of
317 * fences, such as used by struct dma_resv. When using a seqlock,
318 * the seqlock must be taken before and checked after a reference to the
319 * fence is acquired (as shown here).
320 *
321 * The caller is required to hold the RCU read lock.
322 */
323static inline struct dma_fence *
324dma_fence_get_rcu_safe(struct dma_fence __rcu **fencep)
325{
326 do {
327 struct dma_fence *fence;
328
329 fence = rcu_dereference(*fencep);
330 if (!fence)
331 return NULL;
332
333 if (!dma_fence_get_rcu(fence))
334 continue;
335
336 /* The atomic_inc_not_zero() inside dma_fence_get_rcu()
337 * provides a full memory barrier upon success (such as now).
338 * This is paired with the write barrier from assigning
339 * to the __rcu protected fence pointer so that if that
340 * pointer still matches the current fence, we know we
341 * have successfully acquire a reference to it. If it no
342 * longer matches, we are holding a reference to some other
343 * reallocated pointer. This is possible if the allocator
344 * is using a freelist like SLAB_TYPESAFE_BY_RCU where the
345 * fence remains valid for the RCU grace period, but it
346 * may be reallocated. When using such allocators, we are
347 * responsible for ensuring the reference we get is to
348 * the right fence, as below.
349 */
350 if (fence == rcu_access_pointer(*fencep))
351 return rcu_pointer_handoff(fence);
352
353 dma_fence_put(fence);
354 } while (1);
355}
356
357#ifdef CONFIG_LOCKDEP
358bool dma_fence_begin_signalling(void);
359void dma_fence_end_signalling(bool cookie);
360void __dma_fence_might_wait(void);
361#else
362static inline bool dma_fence_begin_signalling(void)
363{
364 return true;
365}
366static inline void dma_fence_end_signalling(bool cookie) {}
367static inline void __dma_fence_might_wait(void) {}
368#endif
369
370int dma_fence_signal(struct dma_fence *fence);
371int dma_fence_signal_locked(struct dma_fence *fence);
372int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
373int dma_fence_signal_timestamp_locked(struct dma_fence *fence,
374 ktime_t timestamp);
375signed long dma_fence_default_wait(struct dma_fence *fence,
376 bool intr, signed long timeout);
377int dma_fence_add_callback(struct dma_fence *fence,
378 struct dma_fence_cb *cb,
379 dma_fence_func_t func);
380bool dma_fence_remove_callback(struct dma_fence *fence,
381 struct dma_fence_cb *cb);
382void dma_fence_enable_sw_signaling(struct dma_fence *fence);
383
384/**
385 * dma_fence_is_signaled_locked - Return an indication if the fence
386 * is signaled yet.
387 * @fence: the fence to check
388 *
389 * Returns true if the fence was already signaled, false if not. Since this
390 * function doesn't enable signaling, it is not guaranteed to ever return
391 * true if dma_fence_add_callback(), dma_fence_wait() or
392 * dma_fence_enable_sw_signaling() haven't been called before.
393 *
394 * This function requires &dma_fence.lock to be held.
395 *
396 * See also dma_fence_is_signaled().
397 */
398static inline bool
399dma_fence_is_signaled_locked(struct dma_fence *fence)
400{
401 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
402 return true;
403
404 if (fence->ops->signaled && fence->ops->signaled(fence)) {
405 dma_fence_signal_locked(fence);
406 return true;
407 }
408
409 return false;
410}
411
412/**
413 * dma_fence_is_signaled - Return an indication if the fence is signaled yet.
414 * @fence: the fence to check
415 *
416 * Returns true if the fence was already signaled, false if not. Since this
417 * function doesn't enable signaling, it is not guaranteed to ever return
418 * true if dma_fence_add_callback(), dma_fence_wait() or
419 * dma_fence_enable_sw_signaling() haven't been called before.
420 *
421 * It's recommended for seqno fences to call dma_fence_signal when the
422 * operation is complete, it makes it possible to prevent issues from
423 * wraparound between time of issue and time of use by checking the return
424 * value of this function before calling hardware-specific wait instructions.
425 *
426 * See also dma_fence_is_signaled_locked().
427 */
428static inline bool
429dma_fence_is_signaled(struct dma_fence *fence)
430{
431 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
432 return true;
433
434 if (fence->ops->signaled && fence->ops->signaled(fence)) {
435 dma_fence_signal(fence);
436 return true;
437 }
438
439 return false;
440}
441
442/**
443 * __dma_fence_is_later - return if f1 is chronologically later than f2
444 * @f1: the first fence's seqno
445 * @f2: the second fence's seqno from the same context
446 * @ops: dma_fence_ops associated with the seqno
447 *
448 * Returns true if f1 is chronologically later than f2. Both fences must be
449 * from the same context, since a seqno is not common across contexts.
450 */
451static inline bool __dma_fence_is_later(u64 f1, u64 f2,
452 const struct dma_fence_ops *ops)
453{
454 /* This is for backward compatibility with drivers which can only handle
455 * 32bit sequence numbers. Use a 64bit compare when the driver says to
456 * do so.
457 */
458 if (ops->use_64bit_seqno)
459 return f1 > f2;
460
461 return (int)(lower_32_bits(f1) - lower_32_bits(f2)) > 0;
462}
463
464/**
465 * dma_fence_is_later - return if f1 is chronologically later than f2
466 * @f1: the first fence from the same context
467 * @f2: the second fence from the same context
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 re-used across contexts.
471 */
472static inline bool dma_fence_is_later(struct dma_fence *f1,
473 struct dma_fence *f2)
474{
475 if (WARN_ON(f1->context != f2->context))
476 return false;
477
478 return __dma_fence_is_later(f1: f1->seqno, f2: f2->seqno, ops: f1->ops);
479}
480
481/**
482 * dma_fence_is_later_or_same - return true if f1 is later or same as f2
483 * @f1: the first fence from the same context
484 * @f2: the second fence from the same context
485 *
486 * Returns true if f1 is chronologically later than f2 or the same fence. Both
487 * fences must be from the same context, since a seqno is not re-used across
488 * contexts.
489 */
490static inline bool dma_fence_is_later_or_same(struct dma_fence *f1,
491 struct dma_fence *f2)
492{
493 return f1 == f2 || dma_fence_is_later(f1, f2);
494}
495
496/**
497 * dma_fence_later - return the chronologically later fence
498 * @f1: the first fence from the same context
499 * @f2: the second fence from the same context
500 *
501 * Returns NULL if both fences are signaled, otherwise the fence that would be
502 * signaled last. Both fences must be from the same context, since a seqno is
503 * not re-used across contexts.
504 */
505static inline struct dma_fence *dma_fence_later(struct dma_fence *f1,
506 struct dma_fence *f2)
507{
508 if (WARN_ON(f1->context != f2->context))
509 return NULL;
510
511 /*
512 * Can't check just DMA_FENCE_FLAG_SIGNALED_BIT here, it may never
513 * have been set if enable_signaling wasn't called, and enabling that
514 * here is overkill.
515 */
516 if (dma_fence_is_later(f1, f2))
517 return dma_fence_is_signaled(fence: f1) ? NULL : f1;
518 else
519 return dma_fence_is_signaled(fence: f2) ? NULL : f2;
520}
521
522/**
523 * dma_fence_get_status_locked - returns the status upon completion
524 * @fence: the dma_fence to query
525 *
526 * Drivers can supply an optional error status condition before they signal
527 * the fence (to indicate whether the fence was completed due to an error
528 * rather than success). The value of the status condition is only valid
529 * if the fence has been signaled, dma_fence_get_status_locked() first checks
530 * the signal state before reporting the error status.
531 *
532 * Returns 0 if the fence has not yet been signaled, 1 if the fence has
533 * been signaled without an error condition, or a negative error code
534 * if the fence has been completed in err.
535 */
536static inline int dma_fence_get_status_locked(struct dma_fence *fence)
537{
538 if (dma_fence_is_signaled_locked(fence))
539 return fence->error ?: 1;
540 else
541 return 0;
542}
543
544int dma_fence_get_status(struct dma_fence *fence);
545
546/**
547 * dma_fence_set_error - flag an error condition on the fence
548 * @fence: the dma_fence
549 * @error: the error to store
550 *
551 * Drivers can supply an optional error status condition before they signal
552 * the fence, to indicate that the fence was completed due to an error
553 * rather than success. This must be set before signaling (so that the value
554 * is visible before any waiters on the signal callback are woken). This
555 * helper exists to help catching erroneous setting of #dma_fence.error.
556 *
557 * Examples of error codes which drivers should use:
558 *
559 * * %-ENODATA This operation produced no data, no other operation affected.
560 * * %-ECANCELED All operations from the same context have been canceled.
561 * * %-ETIME Operation caused a timeout and potentially device reset.
562 */
563static inline void dma_fence_set_error(struct dma_fence *fence,
564 int error)
565{
566 WARN_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
567 WARN_ON(error >= 0 || error < -MAX_ERRNO);
568
569 fence->error = error;
570}
571
572/**
573 * dma_fence_timestamp - helper to get the completion timestamp of a fence
574 * @fence: fence to get the timestamp from.
575 *
576 * After a fence is signaled the timestamp is updated with the signaling time,
577 * but setting the timestamp can race with tasks waiting for the signaling. This
578 * helper busy waits for the correct timestamp to appear.
579 */
580static inline ktime_t dma_fence_timestamp(struct dma_fence *fence)
581{
582 if (WARN_ON(!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)))
583 return ktime_get();
584
585 while (!test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags))
586 cpu_relax();
587
588 return fence->timestamp;
589}
590
591signed long dma_fence_wait_timeout(struct dma_fence *,
592 bool intr, signed long timeout);
593signed long dma_fence_wait_any_timeout(struct dma_fence **fences,
594 uint32_t count,
595 bool intr, signed long timeout,
596 uint32_t *idx);
597
598/**
599 * dma_fence_wait - sleep until the fence gets signaled
600 * @fence: the fence to wait on
601 * @intr: if true, do an interruptible wait
602 *
603 * This function will return -ERESTARTSYS if interrupted by a signal,
604 * or 0 if the fence was signaled. Other error values may be
605 * returned on custom implementations.
606 *
607 * Performs a synchronous wait on this fence. It is assumed the caller
608 * directly or indirectly holds a reference to the fence, otherwise the
609 * fence might be freed before return, resulting in undefined behavior.
610 *
611 * See also dma_fence_wait_timeout() and dma_fence_wait_any_timeout().
612 */
613static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
614{
615 signed long ret;
616
617 /* Since dma_fence_wait_timeout cannot timeout with
618 * MAX_SCHEDULE_TIMEOUT, only valid return values are
619 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
620 */
621 ret = dma_fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
622
623 return ret < 0 ? ret : 0;
624}
625
626void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
627
628struct dma_fence *dma_fence_get_stub(void);
629struct dma_fence *dma_fence_allocate_private_stub(ktime_t timestamp);
630u64 dma_fence_context_alloc(unsigned num);
631
632extern const struct dma_fence_ops dma_fence_array_ops;
633extern const struct dma_fence_ops dma_fence_chain_ops;
634
635/**
636 * dma_fence_is_array - check if a fence is from the array subclass
637 * @fence: the fence to test
638 *
639 * Return true if it is a dma_fence_array and false otherwise.
640 */
641static inline bool dma_fence_is_array(struct dma_fence *fence)
642{
643 return fence->ops == &dma_fence_array_ops;
644}
645
646/**
647 * dma_fence_is_chain - check if a fence is from the chain subclass
648 * @fence: the fence to test
649 *
650 * Return true if it is a dma_fence_chain and false otherwise.
651 */
652static inline bool dma_fence_is_chain(struct dma_fence *fence)
653{
654 return fence->ops == &dma_fence_chain_ops;
655}
656
657/**
658 * dma_fence_is_container - check if a fence is a container for other fences
659 * @fence: the fence to test
660 *
661 * Return true if this fence is a container for other fences, false otherwise.
662 * This is important since we can't build up large fence structure or otherwise
663 * we run into recursion during operation on those fences.
664 */
665static inline bool dma_fence_is_container(struct dma_fence *fence)
666{
667 return dma_fence_is_array(fence) || dma_fence_is_chain(fence);
668}
669
670#endif /* __LINUX_DMA_FENCE_H */
671

source code of linux/include/linux/dma-fence.h