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);