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_ENABLE_SIGNAL_BIT - enable_signaling might have been called
59 * DMA_FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
60 * implementer of the fence for its own purposes. Can be used in different
61 * ways by different fence implementers, so do not rely on this.
63 * Since atomic bitops are used, this is not guaranteed to be the case.
64 * Particularly, if the bit was set, but dma_fence_signal was called right
65 * before this bit was set, it would have been able to set the
66 * DMA_FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
67 * Adding a check for DMA_FENCE_FLAG_SIGNALED_BIT after setting
68 * DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
69 * after dma_fence_signal was called, any enable_signaling call will have either
70 * been completed, or never called at all.
74 const struct dma_fence_ops
*ops
;
76 struct list_head cb_list
;
85 enum dma_fence_flag_bits
{
86 DMA_FENCE_FLAG_SIGNALED_BIT
,
87 DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT
,
88 DMA_FENCE_FLAG_USER_BITS
, /* must always be last member */
91 typedef void (*dma_fence_func_t
)(struct dma_fence
*fence
,
92 struct dma_fence_cb
*cb
);
95 * struct dma_fence_cb - callback for dma_fence_add_callback
96 * @node: used by dma_fence_add_callback to append this struct to fence::cb_list
97 * @func: dma_fence_func_t to call
99 * This struct will be initialized by dma_fence_add_callback, additional
100 * data can be passed along by embedding dma_fence_cb in another struct.
102 struct dma_fence_cb
{
103 struct list_head node
;
104 dma_fence_func_t func
;
108 * struct dma_fence_ops - operations implemented for fence
109 * @get_driver_name: returns the driver name.
110 * @get_timeline_name: return the name of the context this fence belongs to.
111 * @enable_signaling: enable software signaling of fence.
112 * @signaled: [optional] peek whether the fence is signaled, can be null.
113 * @wait: custom wait implementation, or dma_fence_default_wait.
114 * @release: [optional] called on destruction of fence, can be null
115 * @fill_driver_data: [optional] callback to fill in free-form debug info
116 * Returns amount of bytes filled, or -errno.
117 * @fence_value_str: [optional] fills in the value of the fence as a string
118 * @timeline_value_str: [optional] fills in the current value of the timeline
121 * Notes on enable_signaling:
122 * For fence implementations that have the capability for hw->hw
123 * signaling, they can implement this op to enable the necessary
124 * irqs, or insert commands into cmdstream, etc. This is called
125 * in the first wait() or add_callback() path to let the fence
126 * implementation know that there is another driver waiting on
127 * the signal (ie. hw->sw case).
129 * This function can be called called from atomic context, but not
130 * from irq context, so normal spinlocks can be used.
132 * A return value of false indicates the fence already passed,
133 * or some failure occurred that made it impossible to enable
134 * signaling. True indicates successful enabling.
136 * fence->error may be set in enable_signaling, but only when false is
139 * Calling dma_fence_signal before enable_signaling is called allows
140 * for a tiny race window in which enable_signaling is called during,
141 * before, or after dma_fence_signal. To fight this, it is recommended
142 * that before enable_signaling returns true an extra reference is
143 * taken on the fence, to be released when the fence is signaled.
144 * This will mean dma_fence_signal will still be called twice, but
145 * the second time will be a noop since it was already signaled.
148 * May set fence->error if returning true.
151 * Must not be NULL, set to dma_fence_default_wait for default implementation.
152 * the dma_fence_default_wait implementation should work for any fence, as long
153 * as enable_signaling works correctly.
155 * Must return -ERESTARTSYS if the wait is intr = true and the wait was
156 * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
157 * timed out. Can also return other error values on custom implementations,
158 * which should be treated as if the fence is signaled. For example a hardware
159 * lockup could be reported like that.
162 * Can be NULL, this function allows additional commands to run on
163 * destruction of the fence. Can be called from irq context.
164 * If pointer is set to NULL, kfree will get called instead.
167 struct dma_fence_ops
{
168 const char * (*get_driver_name
)(struct dma_fence
*fence
);
169 const char * (*get_timeline_name
)(struct dma_fence
*fence
);
170 bool (*enable_signaling
)(struct dma_fence
*fence
);
171 bool (*signaled
)(struct dma_fence
*fence
);
172 signed long (*wait
)(struct dma_fence
*fence
,
173 bool intr
, signed long timeout
);
174 void (*release
)(struct dma_fence
*fence
);
176 int (*fill_driver_data
)(struct dma_fence
*fence
, void *data
, int size
);
177 void (*fence_value_str
)(struct dma_fence
*fence
, char *str
, int size
);
178 void (*timeline_value_str
)(struct dma_fence
*fence
,
179 char *str
, int size
);
182 void dma_fence_init(struct dma_fence
*fence
, const struct dma_fence_ops
*ops
,
183 spinlock_t
*lock
, u64 context
, unsigned seqno
);
185 void dma_fence_release(struct kref
*kref
);
186 void dma_fence_free(struct dma_fence
*fence
);
189 * dma_fence_put - decreases refcount of the fence
190 * @fence: [in] fence to reduce refcount of
192 static inline void dma_fence_put(struct dma_fence
*fence
)
195 kref_put(&fence
->refcount
, dma_fence_release
);
199 * dma_fence_get - increases refcount of the fence
200 * @fence: [in] fence to increase refcount of
202 * Returns the same fence, with refcount increased by 1.
204 static inline struct dma_fence
*dma_fence_get(struct dma_fence
*fence
)
207 kref_get(&fence
->refcount
);
212 * dma_fence_get_rcu - get a fence from a reservation_object_list with
214 * @fence: [in] fence to increase refcount of
216 * Function returns NULL if no refcount could be obtained, or the fence.
218 static inline struct dma_fence
*dma_fence_get_rcu(struct dma_fence
*fence
)
220 if (kref_get_unless_zero(&fence
->refcount
))
227 * dma_fence_get_rcu_safe - acquire a reference to an RCU tracked fence
228 * @fencep: [in] pointer to fence to increase refcount of
230 * Function returns NULL if no refcount could be obtained, or the fence.
231 * This function handles acquiring a reference to a fence that may be
232 * reallocated within the RCU grace period (such as with SLAB_TYPESAFE_BY_RCU),
233 * so long as the caller is using RCU on the pointer to the fence.
235 * An alternative mechanism is to employ a seqlock to protect a bunch of
236 * fences, such as used by struct reservation_object. When using a seqlock,
237 * the seqlock must be taken before and checked after a reference to the
238 * fence is acquired (as shown here).
240 * The caller is required to hold the RCU read lock.
242 static inline struct dma_fence
*
243 dma_fence_get_rcu_safe(struct dma_fence
* __rcu
*fencep
)
246 struct dma_fence
*fence
;
248 fence
= rcu_dereference(*fencep
);
249 if (!fence
|| !dma_fence_get_rcu(fence
))
252 /* The atomic_inc_not_zero() inside dma_fence_get_rcu()
253 * provides a full memory barrier upon success (such as now).
254 * This is paired with the write barrier from assigning
255 * to the __rcu protected fence pointer so that if that
256 * pointer still matches the current fence, we know we
257 * have successfully acquire a reference to it. If it no
258 * longer matches, we are holding a reference to some other
259 * reallocated pointer. This is possible if the allocator
260 * is using a freelist like SLAB_TYPESAFE_BY_RCU where the
261 * fence remains valid for the RCU grace period, but it
262 * may be reallocated. When using such allocators, we are
263 * responsible for ensuring the reference we get is to
264 * the right fence, as below.
266 if (fence
== rcu_access_pointer(*fencep
))
267 return rcu_pointer_handoff(fence
);
269 dma_fence_put(fence
);
273 int dma_fence_signal(struct dma_fence
*fence
);
274 int dma_fence_signal_locked(struct dma_fence
*fence
);
275 signed long dma_fence_default_wait(struct dma_fence
*fence
,
276 bool intr
, signed long timeout
);
277 int dma_fence_add_callback(struct dma_fence
*fence
,
278 struct dma_fence_cb
*cb
,
279 dma_fence_func_t func
);
280 bool dma_fence_remove_callback(struct dma_fence
*fence
,
281 struct dma_fence_cb
*cb
);
282 void dma_fence_enable_sw_signaling(struct dma_fence
*fence
);
285 * dma_fence_is_signaled_locked - Return an indication if the fence
287 * @fence: [in] the fence to check
289 * Returns true if the fence was already signaled, false if not. Since this
290 * function doesn't enable signaling, it is not guaranteed to ever return
291 * true if dma_fence_add_callback, dma_fence_wait or
292 * dma_fence_enable_sw_signaling haven't been called before.
294 * This function requires fence->lock to be held.
297 dma_fence_is_signaled_locked(struct dma_fence
*fence
)
299 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT
, &fence
->flags
))
302 if (fence
->ops
->signaled
&& fence
->ops
->signaled(fence
)) {
303 dma_fence_signal_locked(fence
);
311 * dma_fence_is_signaled - Return an indication if the fence is signaled yet.
312 * @fence: [in] the fence to check
314 * Returns true if the fence was already signaled, false if not. Since this
315 * function doesn't enable signaling, it is not guaranteed to ever return
316 * true if dma_fence_add_callback, dma_fence_wait or
317 * dma_fence_enable_sw_signaling haven't been called before.
319 * It's recommended for seqno fences to call dma_fence_signal when the
320 * operation is complete, it makes it possible to prevent issues from
321 * wraparound between time of issue and time of use by checking the return
322 * value of this function before calling hardware-specific wait instructions.
325 dma_fence_is_signaled(struct dma_fence
*fence
)
327 if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT
, &fence
->flags
))
330 if (fence
->ops
->signaled
&& fence
->ops
->signaled(fence
)) {
331 dma_fence_signal(fence
);
339 * dma_fence_is_later - return if f1 is chronologically later than f2
340 * @f1: [in] the first fence from the same context
341 * @f2: [in] the second fence from the same context
343 * Returns true if f1 is chronologically later than f2. Both fences must be
344 * from the same context, since a seqno is not re-used across contexts.
346 static inline bool dma_fence_is_later(struct dma_fence
*f1
,
347 struct dma_fence
*f2
)
349 if (WARN_ON(f1
->context
!= f2
->context
))
352 return (int)(f1
->seqno
- f2
->seqno
) > 0;
356 * dma_fence_later - return the chronologically later fence
357 * @f1: [in] the first fence from the same context
358 * @f2: [in] the second fence from the same context
360 * Returns NULL if both fences are signaled, otherwise the fence that would be
361 * signaled last. Both fences must be from the same context, since a seqno is
362 * not re-used across contexts.
364 static inline struct dma_fence
*dma_fence_later(struct dma_fence
*f1
,
365 struct dma_fence
*f2
)
367 if (WARN_ON(f1
->context
!= f2
->context
))
371 * Can't check just DMA_FENCE_FLAG_SIGNALED_BIT here, it may never
372 * have been set if enable_signaling wasn't called, and enabling that
375 if (dma_fence_is_later(f1
, f2
))
376 return dma_fence_is_signaled(f1
) ? NULL
: f1
;
378 return dma_fence_is_signaled(f2
) ? NULL
: f2
;
382 * dma_fence_get_status_locked - returns the status upon completion
383 * @fence: [in] the dma_fence to query
385 * Drivers can supply an optional error status condition before they signal
386 * the fence (to indicate whether the fence was completed due to an error
387 * rather than success). The value of the status condition is only valid
388 * if the fence has been signaled, dma_fence_get_status_locked() first checks
389 * the signal state before reporting the error status.
391 * Returns 0 if the fence has not yet been signaled, 1 if the fence has
392 * been signaled without an error condition, or a negative error code
393 * if the fence has been completed in err.
395 static inline int dma_fence_get_status_locked(struct dma_fence
*fence
)
397 if (dma_fence_is_signaled_locked(fence
))
398 return fence
->error
?: 1;
403 int dma_fence_get_status(struct dma_fence
*fence
);
406 * dma_fence_set_error - flag an error condition on the fence
407 * @fence: [in] the dma_fence
408 * @error: [in] the error to store
410 * Drivers can supply an optional error status condition before they signal
411 * the fence, to indicate that the fence was completed due to an error
412 * rather than success. This must be set before signaling (so that the value
413 * is visible before any waiters on the signal callback are woken). This
414 * helper exists to help catching erroneous setting of #dma_fence.error.
416 static inline void dma_fence_set_error(struct dma_fence
*fence
,
419 BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT
, &fence
->flags
));
420 BUG_ON(error
>= 0 || error
< -MAX_ERRNO
);
422 fence
->error
= error
;
425 signed long dma_fence_wait_timeout(struct dma_fence
*,
426 bool intr
, signed long timeout
);
427 signed long dma_fence_wait_any_timeout(struct dma_fence
**fences
,
429 bool intr
, signed long timeout
,
433 * dma_fence_wait - sleep until the fence gets signaled
434 * @fence: [in] the fence to wait on
435 * @intr: [in] if true, do an interruptible wait
437 * This function will return -ERESTARTSYS if interrupted by a signal,
438 * or 0 if the fence was signaled. Other error values may be
439 * returned on custom implementations.
441 * Performs a synchronous wait on this fence. It is assumed the caller
442 * directly or indirectly holds a reference to the fence, otherwise the
443 * fence might be freed before return, resulting in undefined behavior.
445 static inline signed long dma_fence_wait(struct dma_fence
*fence
, bool intr
)
449 /* Since dma_fence_wait_timeout cannot timeout with
450 * MAX_SCHEDULE_TIMEOUT, only valid return values are
451 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
453 ret
= dma_fence_wait_timeout(fence
, intr
, MAX_SCHEDULE_TIMEOUT
);
455 return ret
< 0 ? ret
: 0;
458 u64
dma_fence_context_alloc(unsigned num
);
460 #define DMA_FENCE_TRACE(f, fmt, args...) \
462 struct dma_fence *__ff = (f); \
463 if (IS_ENABLED(CONFIG_DMA_FENCE_TRACE)) \
464 pr_info("f %llu#%u: " fmt, \
465 __ff->context, __ff->seqno, ##args); \
468 #define DMA_FENCE_WARN(f, fmt, args...) \
470 struct dma_fence *__ff = (f); \
471 pr_warn("f %llu#%u: " fmt, __ff->context, __ff->seqno, \
475 #define DMA_FENCE_ERR(f, fmt, args...) \
477 struct dma_fence *__ff = (f); \
478 pr_err("f %llu#%u: " fmt, __ff->context, __ff->seqno, \
482 #endif /* __LINUX_DMA_FENCE_H */