2 * Fence mechanism for dma-buf to allow for asynchronous dma access
4 * Copyright (C) 2012 Canonical Ltd
5 * Copyright (C) 2012 Texas Instruments
8 * Rob Clark <robdclark@gmail.com>
9 * Maarten Lankhorst <maarten.lankhorst@canonical.com>
11 * This program is free software; you can redistribute it and/or modify it
12 * under the terms of the GNU General Public License version 2 as published by
13 * the Free Software Foundation.
15 * This program is distributed in the hope that it will be useful, but WITHOUT
16 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
17 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
21 #ifndef __LINUX_DMA_FENCE_H
22 #define __LINUX_DMA_FENCE_H
24 #include <linux/err.h>
25 #include <linux/wait.h>
26 #include <linux/list.h>
27 #include <linux/bitops.h>
28 #include <linux/kref.h>
29 #include <linux/sched.h>
30 #include <linux/printk.h>
31 #include <linux/rcupdate.h>
38 * struct dma_fence - software synchronization primitive
39 * @refcount: refcount for this fence
40 * @ops: dma_fence_ops associated with this fence
41 * @rcu: used for releasing fence with kfree_rcu
42 * @cb_list: list of all callbacks to call
43 * @lock: spin_lock_irqsave used for locking
44 * @context: execution context this fence belongs to, returned by
45 * dma_fence_context_alloc()
46 * @seqno: the sequence number of this fence inside the execution context,
47 * can be compared to decide which fence would be signaled later.
48 * @flags: A mask of DMA_FENCE_FLAG_* defined below
49 * @timestamp: Timestamp when the fence was signaled.
50 * @error: Optional, only valid if < 0, must be set before calling
51 * dma_fence_signal, indicates that the fence has completed with an error.
53 * the flags member must be manipulated and read using the appropriate
54 * atomic ops (bit_*), so taking the spinlock will not be needed most
57 * DMA_FENCE_FLAG_SIGNALED_BIT - fence is already signaled
58 * DMA_FENCE_FLAG_TIMESTAMP_BIT - timestamp recorded for fence signaling
59 * DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called
60 * DMA_FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
61 * implementer of the fence for its own purposes. Can be used in different
62 * ways by different fence implementers, so do not rely on this.
64 * Since atomic bitops are used, this is not guaranteed to be the case.
65 * Particularly, if the bit was set, but dma_fence_signal was called right
66 * before this bit was set, it would have been able to set the
67 * DMA_FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
68 * Adding a check for DMA_FENCE_FLAG_SIGNALED_BIT after setting
69 * DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
70 * after dma_fence_signal was called, any enable_signaling call will have either
71 * been completed, or never called at all.
75 const struct dma_fence_ops
*ops
;
77 struct list_head cb_list
;
86 enum dma_fence_flag_bits
{
87 DMA_FENCE_FLAG_SIGNALED_BIT
,
88 DMA_FENCE_FLAG_TIMESTAMP_BIT
,
89 DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT
,
90 DMA_FENCE_FLAG_USER_BITS
, /* must always be last member */
93 typedef void (*dma_fence_func_t
)(struct dma_fence
*fence
,
94 struct dma_fence_cb
*cb
);
97 * struct dma_fence_cb - callback for dma_fence_add_callback()
98 * @node: used by dma_fence_add_callback() to append this struct to fence::cb_list
99 * @func: dma_fence_func_t to call
101 * This struct will be initialized by dma_fence_add_callback(), additional
102 * data can be passed along by embedding dma_fence_cb in another struct.
104 struct dma_fence_cb
{
105 struct list_head node
;
106 dma_fence_func_t func
;
110 * struct dma_fence_ops - operations implemented for fence
113 struct dma_fence_ops
{
117 * Returns the driver name. This is a callback to allow drivers to
118 * compute the name at runtime, without having it to store permanently
119 * for each fence, or build a cache of some sort.
121 * This callback is mandatory.
123 const char * (*get_driver_name
)(struct dma_fence
*fence
);
126 * @get_timeline_name:
128 * Return the name of the context this fence belongs to. This is a
129 * callback to allow drivers to compute the name at runtime, without
130 * having it to store permanently for each fence, or build a cache of
133 * This callback is mandatory.
135 const char * (*get_timeline_name
)(struct dma_fence
*fence
);
140 * Enable software signaling of fence.
142 * For fence implementations that have the capability for hw->hw
143 * signaling, they can implement this op to enable the necessary
144 * interrupts, or insert commands into cmdstream, etc, to avoid these
145 * costly operations for the common case where only hw->hw
146 * synchronization is required. This is called in the first
147 * dma_fence_wait() or dma_fence_add_callback() path to let the fence
148 * implementation know that there is another driver waiting on the
149 * signal (ie. hw->sw case).
151 * This function can be called from atomic context, but not
152 * from irq context, so normal spinlocks can be used.
154 * A return value of false indicates the fence already passed,
155 * or some failure occurred that made it impossible to enable
156 * signaling. True indicates successful enabling.
158 * &dma_fence.error may be set in enable_signaling, but only when false
161 * Since many implementations can call dma_fence_signal() even when before
162 * @enable_signaling has been called there's a race window, where the
163 * dma_fence_signal() might result in the final fence reference being
164 * released and its memory freed. To avoid this, implementations of this
165 * callback should grab their own reference using dma_fence_get(), to be
166 * released when the fence is signalled (through e.g. the interrupt
169 * This callback is optional. If this callback is not present, then the
170 * driver must always have signaling enabled.
172 bool (*enable_signaling
)(struct dma_fence
*fence
);
177 * Peek whether the fence is signaled, as a fastpath optimization for
178 * e.g. dma_fence_wait() or dma_fence_add_callback(). Note that this
179 * callback does not need to make any guarantees beyond that a fence
180 * once indicates as signalled must always return true from this
181 * callback. This callback may return false even if the fence has
182 * completed already, in this case information hasn't propogated throug
183 * the system yet. See also dma_fence_is_signaled().
185 * May set &dma_fence.error if returning true.
187 * This callback is optional.
189 bool (*signaled
)(struct dma_fence
*fence
);
194 * Custom wait implementation, defaults to dma_fence_default_wait() if
197 * The dma_fence_default_wait implementation should work for any fence, as long
198 * as @enable_signaling works correctly. This hook allows drivers to
199 * have an optimized version for the case where a process context is
200 * already available, e.g. if @enable_signaling for the general case
201 * needs to set up a worker thread.
203 * Must return -ERESTARTSYS if the wait is intr = true and the wait was
204 * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
205 * timed out. Can also return other error values on custom implementations,
206 * which should be treated as if the fence is signaled. For example a hardware
207 * lockup could be reported like that.
209 * This callback is optional.
211 signed long (*wait
)(struct dma_fence
*fence
,
212 bool intr
, signed long timeout
);
217 * Called on destruction of fence to release additional resources.
218 * Can be called from irq context. This callback is optional. If it is
219 * NULL, then dma_fence_free() is instead called as the default
222 void (*release
)(struct dma_fence
*fence
);
227 * Callback to fill in free-form debug info specific to this fence, like
228 * the sequence number.
230 * This callback is optional.
232 void (*fence_value_str
)(struct dma_fence
*fence
, char *str
, int size
);
235 * @timeline_value_str:
237 * Fills in the current value of the timeline as a string, like the
238 * sequence number. Note that the specific fence passed to this function
239 * should not matter, drivers should only use it to look up the
240 * corresponding timeline structures.
242 void (*timeline_value_str
)(struct dma_fence
*fence
,
243 char *str
, int size
);
246 void dma_fence_init(struct dma_fence
*fence
, const struct dma_fence_ops
*ops
,
247 spinlock_t
*lock
, u64 context
, unsigned seqno
);
249 void dma_fence_release(struct kref
*kref
);
250 void dma_fence_free(struct dma_fence
*fence
);
253 * dma_fence_put - decreases refcount of the fence
254 * @fence: fence to reduce refcount of
256 static inline void dma_fence_put(struct dma_fence
*fence
)
259 kref_put(&fence
->refcount
, dma_fence_release
);
263 * dma_fence_get - increases refcount of the fence
264 * @fence: fence to increase refcount of
266 * Returns the same fence, with refcount increased by 1.
268 static inline struct dma_fence
*dma_fence_get(struct dma_fence
*fence
)
271 kref_get(&fence
->refcount
);
276 * dma_fence_get_rcu - get a fence from a reservation_object_list with
278 * @fence: fence to increase refcount of
280 * Function returns NULL if no refcount could be obtained, or the fence.
282 static inline struct dma_fence
*dma_fence_get_rcu(struct dma_fence
*fence
)
284 if (kref_get_unless_zero(&fence
->refcount
))
291 * dma_fence_get_rcu_safe - acquire a reference to an RCU tracked fence
292 * @fencep: pointer to fence to increase refcount of
294 * Function returns NULL if no refcount could be obtained, or the fence.
295 * This function handles acquiring a reference to a fence that may be
296 * reallocated within the RCU grace period (such as with SLAB_TYPESAFE_BY_RCU),
297 * so long as the caller is using RCU on the pointer to the fence.
299 * An alternative mechanism is to employ a seqlock to protect a bunch of
300 * fences, such as used by struct reservation_object. When using a seqlock,
301 * the seqlock must be taken before and checked after a reference to the
302 * fence is acquired (as shown here).
304 * The caller is required to hold the RCU read lock.
306 static inline struct dma_fence
*
307 dma_fence_get_rcu_safe(struct dma_fence __rcu
**fencep
)
310 struct dma_fence
*fence
;
312 fence
= rcu_dereference(*fencep
);
316 if (!dma_fence_get_rcu(fence
))
319 /* The atomic_inc_not_zero() inside dma_fence_get_rcu()
320 * provides a full memory barrier upon success (such as now).
321 * This is paired with the write barrier from assigning
322 * to the __rcu protected fence pointer so that if that
323 * pointer still matches the current fence, we know we
324 * have successfully acquire a reference to it. If it no
325 * longer matches, we are holding a reference to some other
326 * reallocated pointer. This is possible if the allocator
327 * is using a freelist like SLAB_TYPESAFE_BY_RCU where the
328 * fence remains valid for the RCU grace period, but it
329 * may be reallocated. When using such allocators, we are
330 * responsible for ensuring the reference we get is to
331 * the right fence, as below.
333 if (fence
== rcu_access_pointer(*fencep
))
334 return rcu_pointer_handoff(fence
);
336 dma_fence_put(fence
);
340 int dma_fence_signal(struct dma_fence
*fence
);
341 int dma_fence_signal_locked(struct dma_fence
*fence
);
342 signed long dma_fence_default_wait(struct dma_fence
*fence
,
343 bool intr
, signed long timeout
);
344 int dma_fence_add_callback(struct dma_fence
*fence
,
345 struct dma_fence_cb
*cb
,
346 dma_fence_func_t func
);
347 bool dma_fence_remove_callback(struct dma_fence
*fence
,
348 struct dma_fence_cb
*cb
);
349 void dma_fence_enable_sw_signaling(struct dma_fence
*fence
);
352 * dma_fence_is_signaled_locked - Return an indication if the fence
354 * @fence: the fence to check
356 * Returns true if the fence was already signaled, false if not. Since this
357 * function doesn't enable signaling, it is not guaranteed to ever return
358 * true if dma_fence_add_callback(), dma_fence_wait() or
359 * dma_fence_enable_sw_signaling() haven't been called before.
361 * This function requires &dma_fence.lock to be held.
363 * See also dma_fence_is_signaled().
366 dma_fence_is_signaled_locked(struct dma_fence
*fence
)
368 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT
, &fence
->flags
))
371 if (fence
->ops
->signaled
&& fence
->ops
->signaled(fence
)) {
372 dma_fence_signal_locked(fence
);
380 * dma_fence_is_signaled - Return an indication if the fence is signaled yet.
381 * @fence: the fence to check
383 * Returns true if the fence was already signaled, false if not. Since this
384 * function doesn't enable signaling, it is not guaranteed to ever return
385 * true if dma_fence_add_callback(), dma_fence_wait() or
386 * dma_fence_enable_sw_signaling() haven't been called before.
388 * It's recommended for seqno fences to call dma_fence_signal when the
389 * operation is complete, it makes it possible to prevent issues from
390 * wraparound between time of issue and time of use by checking the return
391 * value of this function before calling hardware-specific wait instructions.
393 * See also dma_fence_is_signaled_locked().
396 dma_fence_is_signaled(struct dma_fence
*fence
)
398 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT
, &fence
->flags
))
401 if (fence
->ops
->signaled
&& fence
->ops
->signaled(fence
)) {
402 dma_fence_signal(fence
);
410 * __dma_fence_is_later - return if f1 is chronologically later than f2
411 * @f1: the first fence's seqno
412 * @f2: the second fence's seqno from the same context
414 * Returns true if f1 is chronologically later than f2. Both fences must be
415 * from the same context, since a seqno is not common across contexts.
417 static inline bool __dma_fence_is_later(u32 f1
, u32 f2
)
419 return (int)(f1
- f2
) > 0;
423 * dma_fence_is_later - return if f1 is chronologically later than f2
424 * @f1: the first fence from the same context
425 * @f2: the second fence from the same context
427 * Returns true if f1 is chronologically later than f2. Both fences must be
428 * from the same context, since a seqno is not re-used across contexts.
430 static inline bool dma_fence_is_later(struct dma_fence
*f1
,
431 struct dma_fence
*f2
)
433 if (WARN_ON(f1
->context
!= f2
->context
))
436 return __dma_fence_is_later(f1
->seqno
, f2
->seqno
);
440 * dma_fence_later - return the chronologically later fence
441 * @f1: the first fence from the same context
442 * @f2: the second fence from the same context
444 * Returns NULL if both fences are signaled, otherwise the fence that would be
445 * signaled last. Both fences must be from the same context, since a seqno is
446 * not re-used across contexts.
448 static inline struct dma_fence
*dma_fence_later(struct dma_fence
*f1
,
449 struct dma_fence
*f2
)
451 if (WARN_ON(f1
->context
!= f2
->context
))
455 * Can't check just DMA_FENCE_FLAG_SIGNALED_BIT here, it may never
456 * have been set if enable_signaling wasn't called, and enabling that
459 if (dma_fence_is_later(f1
, f2
))
460 return dma_fence_is_signaled(f1
) ? NULL
: f1
;
462 return dma_fence_is_signaled(f2
) ? NULL
: f2
;
466 * dma_fence_get_status_locked - returns the status upon completion
467 * @fence: the dma_fence to query
469 * Drivers can supply an optional error status condition before they signal
470 * the fence (to indicate whether the fence was completed due to an error
471 * rather than success). The value of the status condition is only valid
472 * if the fence has been signaled, dma_fence_get_status_locked() first checks
473 * the signal state before reporting the error status.
475 * Returns 0 if the fence has not yet been signaled, 1 if the fence has
476 * been signaled without an error condition, or a negative error code
477 * if the fence has been completed in err.
479 static inline int dma_fence_get_status_locked(struct dma_fence
*fence
)
481 if (dma_fence_is_signaled_locked(fence
))
482 return fence
->error
?: 1;
487 int dma_fence_get_status(struct dma_fence
*fence
);
490 * dma_fence_set_error - flag an error condition on the fence
491 * @fence: the dma_fence
492 * @error: the error to store
494 * Drivers can supply an optional error status condition before they signal
495 * the fence, to indicate that the fence was completed due to an error
496 * rather than success. This must be set before signaling (so that the value
497 * is visible before any waiters on the signal callback are woken). This
498 * helper exists to help catching erroneous setting of #dma_fence.error.
500 static inline void dma_fence_set_error(struct dma_fence
*fence
,
503 WARN_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT
, &fence
->flags
));
504 WARN_ON(error
>= 0 || error
< -MAX_ERRNO
);
506 fence
->error
= error
;
509 signed long dma_fence_wait_timeout(struct dma_fence
*,
510 bool intr
, signed long timeout
);
511 signed long dma_fence_wait_any_timeout(struct dma_fence
**fences
,
513 bool intr
, signed long timeout
,
517 * dma_fence_wait - sleep until the fence gets signaled
518 * @fence: the fence to wait on
519 * @intr: if true, do an interruptible wait
521 * This function will return -ERESTARTSYS if interrupted by a signal,
522 * or 0 if the fence was signaled. Other error values may be
523 * returned on custom implementations.
525 * Performs a synchronous wait on this fence. It is assumed the caller
526 * directly or indirectly holds a reference to the fence, otherwise the
527 * fence might be freed before return, resulting in undefined behavior.
529 * See also dma_fence_wait_timeout() and dma_fence_wait_any_timeout().
531 static inline signed long dma_fence_wait(struct dma_fence
*fence
, bool intr
)
535 /* Since dma_fence_wait_timeout cannot timeout with
536 * MAX_SCHEDULE_TIMEOUT, only valid return values are
537 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
539 ret
= dma_fence_wait_timeout(fence
, intr
, MAX_SCHEDULE_TIMEOUT
);
541 return ret
< 0 ? ret
: 0;
544 u64
dma_fence_context_alloc(unsigned num
);
546 #define DMA_FENCE_TRACE(f, fmt, args...) \
548 struct dma_fence *__ff = (f); \
549 if (IS_ENABLED(CONFIG_DMA_FENCE_TRACE)) \
550 pr_info("f %llu#%u: " fmt, \
551 __ff->context, __ff->seqno, ##args); \
554 #define DMA_FENCE_WARN(f, fmt, args...) \
556 struct dma_fence *__ff = (f); \
557 pr_warn("f %llu#%u: " fmt, __ff->context, __ff->seqno, \
561 #define DMA_FENCE_ERR(f, fmt, args...) \
563 struct dma_fence *__ff = (f); \
564 pr_err("f %llu#%u: " fmt, __ff->context, __ff->seqno, \
568 #endif /* __LINUX_DMA_FENCE_H */