summaryrefslogtreecommitdiffstats
path: root/include/linux/dma-fence.h
blob: 9f12efaaa93ae8d51e2a10445775d3d31eddc952 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Fence mechanism for dma-buf to allow for asynchronous dma access
 *
 * Copyright (C) 2012 Canonical Ltd
 * Copyright (C) 2012 Texas Instruments
 *
 * Authors:
 * Rob Clark <robdclark@gmail.com>
 * Maarten Lankhorst <maarten.lankhorst@canonical.com>
 */

#ifndef __LINUX_DMA_FENCE_H
#define __LINUX_DMA_FENCE_H

#include <linux/err.h>
#include <linux/wait.h>
#include <linux/list.h>
#include <linux/bitops.h>
#include <linux/kref.h>
#include <linux/sched.h>
#include <linux/printk.h>
#include <linux/rcupdate.h>

struct dma_fence;
struct dma_fence_ops;
struct dma_fence_cb;

/**
 * struct dma_fence - software synchronization primitive
 * @refcount: refcount for this fence
 * @ops: dma_fence_ops associated with this fence
 * @rcu: used for releasing fence with kfree_rcu
 * @cb_list: list of all callbacks to call
 * @lock: spin_lock_irqsave used for locking
 * @context: execution context this fence belongs to, returned by
 *           dma_fence_context_alloc()
 * @seqno: the sequence number of this fence inside the execution context,
 * can be compared to decide which fence would be signaled later.
 * @flags: A mask of DMA_FENCE_FLAG_* defined below
 * @timestamp: Timestamp when the fence was signaled.
 * @error: Optional, only valid if < 0, must be set before calling
 * dma_fence_signal, indicates that the fence has completed with an error.
 *
 * the flags member must be manipulated and read using the appropriate
 * atomic ops (bit_*), so taking the spinlock will not be needed most
 * of the time.
 *
 * DMA_FENCE_FLAG_SIGNALED_BIT - fence is already signaled
 * DMA_FENCE_FLAG_TIMESTAMP_BIT - timestamp recorded for fence signaling
 * DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called
 * DMA_FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
 * implementer of the fence for its own purposes. Can be used in different
 * ways by different fence implementers, so do not rely on this.
 *
 * Since atomic bitops are used, this is not guaranteed to be the case.
 * Particularly, if the bit was set, but dma_fence_signal was called right
 * before this bit was set, it would have been able to set the
 * DMA_FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
 * Adding a check for DMA_FENCE_FLAG_SIGNALED_BIT after setting
 * DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
 * after dma_fence_signal was called, any enable_signaling call will have either
 * been completed, or never called at all.
 */
struct dma_fence {
	spinlock_t *lock;
	const struct dma_fence_ops *ops;
	/*
	 * We clear the callback list on kref_put so that by the time we
	 * release the fence it is unused. No one should be adding to the
	 * cb_list that they don't themselves hold a reference for.
	 *
	 * The lifetime of the timestamp is similarly tied to both the
	 * rcu freelist and the cb_list. The timestamp is only set upon
	 * signaling while simultaneously notifying the cb_list. Ergo, we
	 * only use either the cb_list of timestamp. Upon destruction,
	 * neither are accessible, and so we can use the rcu. This means
	 * that the cb_list is *only* valid until the signal bit is set,
	 * and to read either you *must* hold a reference to the fence,
	 * and not just the rcu_read_lock.
	 *
	 * Listed in chronological order.
	 */
	union {
		struct list_head cb_list;
		/* @cb_list replaced by @timestamp on dma_fence_signal() */
		ktime_t timestamp;
		/* @timestamp replaced by @rcu on dma_fence_release() */
		struct rcu_head rcu;
	};
	u64 context;
	u64 seqno;
	unsigned long flags;
	struct kref refcount;
	int error;
};

enum dma_fence_flag_bits {
	DMA_FENCE_FLAG_SIGNALED_BIT,
	DMA_FENCE_FLAG_TIMESTAMP_BIT,
	DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
	DMA_FENCE_FLAG_USER_BITS, /* must always be last member */
};

typedef void (*dma_fence_func_t)(struct dma_fence *fence,
				 struct dma_fence_cb *cb);

/**
 * struct dma_fence_cb - callback for dma_fence_add_callback()
 * @node: used by dma_fence_add_callback() to append this struct to fence::cb_list
 * @func: dma_fence_func_t to call
 *
 * This struct will be initialized by dma_fence_add_callback(), additional
 * data can be passed along by embedding dma_fence_cb in another struct.
 */
struct dma_fence_cb {
	struct list_head node;
	dma_fence_func_t func;
};

/**
 * struct dma_fence_ops - operations implemented for fence
 *
 */
struct dma_fence_ops {
	/**
	 * @use_64bit_seqno:
	 *
	 * True if this dma_fence implementation uses 64bit seqno, false
	 * otherwise.
	 */
	bool use_64bit_seqno;

	/**
	 * @get_driver_name:
	 *
	 * Returns the driver name. This is a callback to allow drivers to
	 * compute the name at runtime, without having it to store permanently
	 * for each fence, or build a cache of some sort.
	 *
	 * This callback is mandatory.
	 */
	const char * (*get_driver_name)(struct dma_fence *fence);

	/**
	 * @get_timeline_name:
	 *
	 * Return the name of the context this fence belongs to. This is a
	 * callback to allow drivers to compute the name at runtime, without
	 * having it to store permanently for each fence, or build a cache of
	 * some sort.
	 *
	 * This callback is mandatory.
	 */
	const char * (*get_timeline_name)(struct dma_fence *fence);

	/**
	 * @enable_signaling:
	 *
	 * Enable software signaling of fence.
	 *
	 * For fence implementations that have the capability for hw->hw
	 * signaling, they can implement this op to enable the necessary
	 * interrupts, or insert commands into cmdstream, etc, to avoid these
	 * costly operations for the common case where only hw->hw
	 * synchronization is required.  This is called in the first
	 * dma_fence_wait() or dma_fence_add_callback() path to let the fence
	 * implementation know that there is another driver waiting on the
	 * signal (ie. hw->sw case).
	 *
	 * This function can be called from atomic context, but not
	 * from irq context, so normal spinlocks can be used.
	 *
	 * A return value of false indicates the fence already passed,
	 * or some failure occurred that made it impossible to enable
	 * signaling. True indicates successful enabling.
	 *
	 * &dma_fence.error may be set in enable_signaling, but only when false
	 * is returned.
	 *
	 * Since many implementations can call dma_fence_signal() even when before
	 * @enable_signaling has been called there's a race window, where the
	 * dma_fence_signal() might result in the final fence reference being
	 * released and its memory freed. To avoid this, implementations of this
	 * callback should grab their own reference using dma_fence_get(), to be
	 * released when the fence is signalled (through e.g. the interrupt
	 * handler).
	 *
	 * This callback is optional. If this callback is not present, then the
	 * driver must always have signaling enabled.
	 */
	bool (*enable_signaling)(struct dma_fence *fence);

	/**
	 * @signaled:
	 *
	 * Peek whether the fence is signaled, as a fastpath optimization for
	 * e.g. dma_fence_wait() or dma_fence_add_callback(). Note that this
	 * callback does not need to make any guarantees beyond that a fence
	 * once indicates as signalled must always return true from this
	 * callback. This callback may return false even if the fence has
	 * completed already, in this case information hasn't propogated throug
	 * the system yet. See also dma_fence_is_signaled().
	 *
	 * May set &dma_fence.error if returning true.
	 *
	 * This callback is optional.
	 */
	bool (*signaled)(struct dma_fence *fence);

	/**
	 * @wait:
	 *
	 * Custom wait implementation, defaults to dma_fence_default_wait() if
	 * not set.
	 *
	 * The dma_fence_default_wait implementation should work for any fence, as long
	 * as @enable_signaling works correctly. This hook allows drivers to
	 * have an optimized version for the case where a process context is
	 * already available, e.g. if @enable_signaling for the general case
	 * needs to set up a worker thread.
	 *
	 * Must return -ERESTARTSYS if the wait is intr = true and the wait was
	 * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
	 * timed out. Can also return other error values on custom implementations,
	 * which should be treated as if the fence is signaled. For example a hardware
	 * lockup could be reported like that.
	 *
	 * This callback is optional.
	 */
	signed long (*wait)(struct dma_fence *fence,
			    bool intr, signed long timeout);

	/**
	 * @release:
	 *
	 * Called on destruction of fence to release additional resources.
	 * Can be called from irq context.  This callback is optional. If it is
	 * NULL, then dma_fence_free() is instead called as the default
	 * implementation.
	 */
	void (*release)(struct dma_fence *fence);

	/**
	 * @fence_value_str:
	 *
	 * Callback to fill in free-form debug info specific to this fence, like
	 * the sequence number.
	 *
	 * This callback is optional.
	 */
	void (*fence_value_str)(struct dma_fence *fence, char *str, int size);

	/**
	 * @timeline_value_str:
	 *
	 * Fills in the current value of the timeline as a string, like the
	 * sequence number. Note that the specific fence passed to this function
	 * should not matter, drivers should only use it to look up the
	 * corresponding timeline structures.
	 */
	void (*timeline_value_str)(struct dma_fence *fence,
				   char *str, int size);
};

void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
		    spinlock_t *lock, u64 context, u64 seqno);

void dma_fence_release(struct kref *kref);
void dma_fence_free(struct dma_fence *fence);

/**
 * dma_fence_put - decreases refcount of the fence
 * @fence: fence to reduce refcount of
 */
static inline void dma_fence_put(struct dma_fence *fence)
{
	if (fence)
		kref_put(&fence->refcount, dma_fence_release);
}

/**
 * dma_fence_get - increases refcount of the fence
 * @fence: fence to increase refcount of
 *
 * Returns the same fence, with refcount increased by 1.
 */
static inline struct dma_fence *dma_fence_get(struct dma_fence *fence)
{
	if (fence)
		kref_get(&fence->refcount);
	return fence;
}

/**
 * dma_fence_get_rcu - get a fence from a dma_resv_list with
 *                     rcu read lock
 * @fence: fence to increase refcount of
 *
 * Function returns NULL if no refcount could be obtained, or the fence.
 */
static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence)
{
	if (kref_get_unless_zero(&fence->refcount))
		return fence;
	else
		return NULL;
}

/**
 * dma_fence_get_rcu_safe  - acquire a reference to an RCU tracked fence
 * @fencep: pointer to fence to increase refcount of
 *
 * Function returns NULL if no refcount could be obtained, or the fence.
 * This function handles acquiring a reference to a fence that may be
 * reallocated within the RCU grace period (such as with SLAB_TYPESAFE_BY_RCU),
 * so long as the caller is using RCU on the pointer to the fence.
 *
 * An alternative mechanism is to employ a seqlock to protect a bunch of
 * fences, such as used by struct dma_resv. When using a seqlock,
 * the seqlock must be taken before and checked after a reference to the
 * fence is acquired (as shown here).
 *
 * The caller is required to hold the RCU read lock.
 */
static inline struct dma_fence *
dma_fence_get_rcu_safe(struct dma_fence __rcu **fencep)
{
	do {
		struct dma_fence *fence;

		fence = rcu_dereference(*fencep);
		if (!fence)
			return NULL;

		if (!dma_fence_get_rcu(fence))
			continue;

		/* The atomic_inc_not_zero() inside dma_fence_get_rcu()
		 * provides a full memory barrier upon success (such as now).
		 * This is paired with the write barrier from assigning
		 * to the __rcu protected fence pointer so that if that
		 * pointer still matches the current fence, we know we
		 * have successfully acquire a reference to it. If it no
		 * longer matches, we are holding a reference to some other
		 * reallocated pointer. This is possible if the allocator
		 * is using a freelist like SLAB_TYPESAFE_BY_RCU where the
		 * fence remains valid for the RCU grace period, but it
		 * may be reallocated. When using such allocators, we are
		 * responsible for ensuring the reference we get is to
		 * the right fence, as below.
		 */
		if (fence == rcu_access_pointer(*fencep))
			return rcu_pointer_handoff(fence);

		dma_fence_put(fence);
	} while (1);
}

#ifdef CONFIG_LOCKDEP
bool dma_fence_begin_signalling(void);
void dma_fence_end_signalling(bool cookie);
void __dma_fence_might_wait(void);
#else
static inline bool dma_fence_begin_signalling(void)
{
	return true;
}
static inline void dma_fence_end_signalling(bool cookie) {}
static inline void __dma_fence_might_wait(void) {}
#endif

int dma_fence_signal(struct dma_fence *fence);
int dma_fence_signal_locked(struct dma_fence *fence);
int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
int dma_fence_signal_timestamp_locked(struct dma_fence *fence,
				      ktime_t timestamp);
signed long dma_fence_default_wait(struct dma_fence *fence,
				   bool intr, signed long timeout);
int dma_fence_add_callback(struct dma_fence *fence,
			   struct dma_fence_cb *cb,
			   dma_fence_func_t func);
bool dma_fence_remove_callback(struct dma_fence *fence,
			       struct dma_fence_cb *cb);
void dma_fence_enable_sw_signaling(struct dma_fence *fence);

/**
 * dma_fence_is_signaled_locked - Return an indication if the fence
 *                                is signaled yet.
 * @fence: the fence to check
 *
 * Returns true if the fence was already signaled, false if not. Since this
 * function doesn't enable signaling, it is not guaranteed to ever return
 * true if dma_fence_add_callback(), dma_fence_wait() or
 * dma_fence_enable_sw_signaling() haven't been called before.
 *
 * This function requires &dma_fence.lock to be held.
 *
 * See also dma_fence_is_signaled().
 */
static inline bool
dma_fence_is_signaled_locked(struct dma_fence *fence)
{
	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
		return true;

	if (fence->ops->signaled && fence->ops->signaled(fence)) {
		dma_fence_signal_locked(fence);
		return true;
	}

	return false;
}

/**
 * dma_fence_is_signaled - Return an indication if the fence is signaled yet.
 * @fence: the fence to check
 *
 * Returns true if the fence was already signaled, false if not. Since this
 * function doesn't enable signaling, it is not guaranteed to ever return
 * true if dma_fence_add_callback(), dma_fence_wait() or
 * dma_fence_enable_sw_signaling() haven't been called before.
 *
 * It's recommended for seqno fences to call dma_fence_signal when the
 * operation is complete, it makes it possible to prevent issues from
 * wraparound between time of issue and time of use by checking the return
 * value of this function before calling hardware-specific wait instructions.
 *
 * See also dma_fence_is_signaled_locked().
 */
static inline bool
dma_fence_is_signaled(struct dma_fence *fence)
{
	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
		return true;

	if (fence->ops->signaled && fence->ops->signaled(fence)) {
		dma_fence_signal(fence);
		return true;
	}

	return false;
}

/**
 * __dma_fence_is_later - return if f1 is chronologically later than f2
 * @f1: the first fence's seqno
 * @f2: the second fence's seqno from the same context
 * @ops: dma_fence_ops associated with the seqno
 *
 * Returns true if f1 is chronologically later than f2. Both fences must be
 * from the same context, since a seqno is not common across contexts.
 */
static inline bool __dma_fence_is_later(u64 f1, u64 f2,
					const struct dma_fence_ops *ops)
{
	/* This is for backward compatibility with drivers which can only handle
	 * 32bit sequence numbers. Use a 64bit compare when the driver says to
	 * do so.
	 */
	if (ops->use_64bit_seqno)
		return f1 > f2;

	return (int)(lower_32_bits(f1) - lower_32_bits(f2)) > 0;
}

/**
 * dma_fence_is_later - return if f1 is chronologically later than f2
 * @f1: the first fence from the same context
 * @f2: the second fence from the same context
 *
 * Returns true if f1 is chronologically later than f2. Both fences must be
 * from the same context, since a seqno is not re-used across contexts.
 */
static inline bool dma_fence_is_later(struct dma_fence *f1,
				      struct dma_fence *f2)
{
	if (WARN_ON(f1->context != f2->context))
		return false;

	return __dma_fence_is_later(f1->seqno, f2->seqno, f1->ops);
}

/**
 * dma_fence_later - return the chronologically later fence
 * @f1:	the first fence from the same context
 * @f2:	the second fence from the same context
 *
 * Returns NULL if both fences are signaled, otherwise the fence that would be
 * signaled last. Both fences must be from the same context, since a seqno is
 * not re-used across contexts.
 */
static inline struct dma_fence *dma_fence_later(struct dma_fence *f1,
						struct dma_fence *f2)
{
	if (WARN_ON(f1->context != f2->context))
		return NULL;

	/*
	 * Can't check just DMA_FENCE_FLAG_SIGNALED_BIT here, it may never
	 * have been set if enable_signaling wasn't called, and enabling that
	 * here is overkill.
	 */
	if (dma_fence_is_later(f1, f2))
		return dma_fence_is_signaled(f1) ? NULL : f1;
	else
		return dma_fence_is_signaled(f2) ? NULL : f2;
}

/**
 * dma_fence_get_status_locked - returns the status upon completion
 * @fence: the dma_fence to query
 *
 * Drivers can supply an optional error status condition before they signal
 * the fence (to indicate whether the fence was completed due to an error
 * rather than success). The value of the status condition is only valid
 * if the fence has been signaled, dma_fence_get_status_locked() first checks
 * the signal state before reporting the error status.
 *
 * Returns 0 if the fence has not yet been signaled, 1 if the fence has
 * been signaled without an error condition, or a negative error code
 * if the fence has been completed in err.
 */
static inline int dma_fence_get_status_locked(struct dma_fence *fence)
{
	if (dma_fence_is_signaled_locked(fence))
		return fence->error ?: 1;
	else
		return 0;
}

int dma_fence_get_status(struct dma_fence *fence);

/**
 * dma_fence_set_error - flag an error condition on the fence
 * @fence: the dma_fence
 * @error: the error to store
 *
 * Drivers can supply an optional error status condition before they signal
 * the fence, to indicate that the fence was completed due to an error
 * rather than success. This must be set before signaling (so that the value
 * is visible before any waiters on the signal callback are woken). This
 * helper exists to help catching erroneous setting of #dma_fence.error.
 */
static inline void dma_fence_set_error(struct dma_fence *fence,
				       int error)
{
	WARN_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
	WARN_ON(error >= 0 || error < -MAX_ERRNO);

	fence->error = error;
}

signed long dma_fence_wait_timeout(struct dma_fence *,
				   bool intr, signed long timeout);
signed long dma_fence_wait_any_timeout(struct dma_fence **fences,
				       uint32_t count,
				       bool intr, signed long timeout,
				       uint32_t *idx);

/**
 * dma_fence_wait - sleep until the fence gets signaled
 * @fence: the fence to wait on
 * @intr: if true, do an interruptible wait
 *
 * This function will return -ERESTARTSYS if interrupted by a signal,
 * or 0 if the fence was signaled. Other error values may be
 * returned on custom implementations.
 *
 * Performs a synchronous wait on this fence. It is assumed the caller
 * directly or indirectly holds a reference to the fence, otherwise the
 * fence might be freed before return, resulting in undefined behavior.
 *
 * See also dma_fence_wait_timeout() and dma_fence_wait_any_timeout().
 */
static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
{
	signed long ret;

	/* Since dma_fence_wait_timeout cannot timeout with
	 * MAX_SCHEDULE_TIMEOUT, only valid return values are
	 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
	 */
	ret = dma_fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);

	return ret < 0 ? ret : 0;
}

struct dma_fence *dma_fence_get_stub(void);
u64 dma_fence_context_alloc(unsigned num);

#define DMA_FENCE_TRACE(f, fmt, args...) \
	do {								\
		struct dma_fence *__ff = (f);				\
		if (IS_ENABLED(CONFIG_DMA_FENCE_TRACE))			\
			pr_info("f %llu#%llu: " fmt,			\
				__ff->context, __ff->seqno, ##args);	\
	} while (0)

#define DMA_FENCE_WARN(f, fmt, args...) \
	do {								\
		struct dma_fence *__ff = (f);				\
		pr_warn("f %llu#%llu: " fmt, __ff->context, __ff->seqno,\
			 ##args);					\
	} while (0)

#define DMA_FENCE_ERR(f, fmt, args...) \
	do {								\
		struct dma_fence *__ff = (f);				\
		pr_err("f %llu#%llu: " fmt, __ff->context, __ff->seqno,	\
			##args);					\
	} while (0)

#endif /* __LINUX_DMA_FENCE_H */