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TOMOYO Linux Cross Reference
Linux/include/linux/dma-fence.h

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  1 /*
  2  * Fence mechanism for dma-buf to allow for asynchronous dma access
  3  *
  4  * Copyright (C) 2012 Canonical Ltd
  5  * Copyright (C) 2012 Texas Instruments
  6  *
  7  * Authors:
  8  * Rob Clark <robdclark@gmail.com>
  9  * Maarten Lankhorst <maarten.lankhorst@canonical.com>
 10  *
 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.
 14  *
 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
 18  * more details.
 19  */
 20 
 21 #ifndef __LINUX_DMA_FENCE_H
 22 #define __LINUX_DMA_FENCE_H
 23 
 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>
 32 
 33 struct dma_fence;
 34 struct dma_fence_ops;
 35 struct dma_fence_cb;
 36 
 37 /**
 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.
 52  *
 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
 55  * of the time.
 56  *
 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.
 63  *
 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.
 72  */
 73 struct dma_fence {
 74         struct kref refcount;
 75         const struct dma_fence_ops *ops;
 76         struct rcu_head rcu;
 77         struct list_head cb_list;
 78         spinlock_t *lock;
 79         u64 context;
 80         unsigned seqno;
 81         unsigned long flags;
 82         ktime_t timestamp;
 83         int error;
 84 };
 85 
 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 */
 91 };
 92 
 93 typedef void (*dma_fence_func_t)(struct dma_fence *fence,
 94                                  struct dma_fence_cb *cb);
 95 
 96 /**
 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
100  *
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.
103  */
104 struct dma_fence_cb {
105         struct list_head node;
106         dma_fence_func_t func;
107 };
108 
109 /**
110  * struct dma_fence_ops - operations implemented for fence
111  *
112  */
113 struct dma_fence_ops {
114         /**
115          * @get_driver_name:
116          *
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.
120          *
121          * This callback is mandatory.
122          */
123         const char * (*get_driver_name)(struct dma_fence *fence);
124 
125         /**
126          * @get_timeline_name:
127          *
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
131          * some sort.
132          *
133          * This callback is mandatory.
134          */
135         const char * (*get_timeline_name)(struct dma_fence *fence);
136 
137         /**
138          * @enable_signaling:
139          *
140          * Enable software signaling of fence.
141          *
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).
150          *
151          * This function can be called from atomic context, but not
152          * from irq context, so normal spinlocks can be used.
153          *
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.
157          *
158          * &dma_fence.error may be set in enable_signaling, but only when false
159          * is returned.
160          *
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
167          * handler).
168          *
169          * This callback is optional. If this callback is not present, then the
170          * driver must always have signaling enabled.
171          */
172         bool (*enable_signaling)(struct dma_fence *fence);
173 
174         /**
175          * @signaled:
176          *
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().
184          *
185          * May set &dma_fence.error if returning true.
186          *
187          * This callback is optional.
188          */
189         bool (*signaled)(struct dma_fence *fence);
190 
191         /**
192          * @wait:
193          *
194          * Custom wait implementation, defaults to dma_fence_default_wait() if
195          * not set.
196          *
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.
202          *
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.
208          *
209          * This callback is optional.
210          */
211         signed long (*wait)(struct dma_fence *fence,
212                             bool intr, signed long timeout);
213 
214         /**
215          * @release:
216          *
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
220          * implementation.
221          */
222         void (*release)(struct dma_fence *fence);
223 
224         /**
225          * @fence_value_str:
226          *
227          * Callback to fill in free-form debug info specific to this fence, like
228          * the sequence number.
229          *
230          * This callback is optional.
231          */
232         void (*fence_value_str)(struct dma_fence *fence, char *str, int size);
233 
234         /**
235          * @timeline_value_str:
236          *
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.
241          */
242         void (*timeline_value_str)(struct dma_fence *fence,
243                                    char *str, int size);
244 };
245 
246 void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
247                     spinlock_t *lock, u64 context, unsigned seqno);
248 
249 void dma_fence_release(struct kref *kref);
250 void dma_fence_free(struct dma_fence *fence);
251 
252 /**
253  * dma_fence_put - decreases refcount of the fence
254  * @fence: fence to reduce refcount of
255  */
256 static inline void dma_fence_put(struct dma_fence *fence)
257 {
258         if (fence)
259                 kref_put(&fence->refcount, dma_fence_release);
260 }
261 
262 /**
263  * dma_fence_get - increases refcount of the fence
264  * @fence: fence to increase refcount of
265  *
266  * Returns the same fence, with refcount increased by 1.
267  */
268 static inline struct dma_fence *dma_fence_get(struct dma_fence *fence)
269 {
270         if (fence)
271                 kref_get(&fence->refcount);
272         return fence;
273 }
274 
275 /**
276  * dma_fence_get_rcu - get a fence from a reservation_object_list with
277  *                     rcu read lock
278  * @fence: fence to increase refcount of
279  *
280  * Function returns NULL if no refcount could be obtained, or the fence.
281  */
282 static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence)
283 {
284         if (kref_get_unless_zero(&fence->refcount))
285                 return fence;
286         else
287                 return NULL;
288 }
289 
290 /**
291  * dma_fence_get_rcu_safe  - acquire a reference to an RCU tracked fence
292  * @fencep: pointer to fence to increase refcount of
293  *
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.
298  *
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).
303  *
304  * The caller is required to hold the RCU read lock.
305  */
306 static inline struct dma_fence *
307 dma_fence_get_rcu_safe(struct dma_fence __rcu **fencep)
308 {
309         do {
310                 struct dma_fence *fence;
311 
312                 fence = rcu_dereference(*fencep);
313                 if (!fence)
314                         return NULL;
315 
316                 if (!dma_fence_get_rcu(fence))
317                         continue;
318 
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.
332                  */
333                 if (fence == rcu_access_pointer(*fencep))
334                         return rcu_pointer_handoff(fence);
335 
336                 dma_fence_put(fence);
337         } while (1);
338 }
339 
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);
350 
351 /**
352  * dma_fence_is_signaled_locked - Return an indication if the fence
353  *                                is signaled yet.
354  * @fence: the fence to check
355  *
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.
360  *
361  * This function requires &dma_fence.lock to be held.
362  *
363  * See also dma_fence_is_signaled().
364  */
365 static inline bool
366 dma_fence_is_signaled_locked(struct dma_fence *fence)
367 {
368         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
369                 return true;
370 
371         if (fence->ops->signaled && fence->ops->signaled(fence)) {
372                 dma_fence_signal_locked(fence);
373                 return true;
374         }
375 
376         return false;
377 }
378 
379 /**
380  * dma_fence_is_signaled - Return an indication if the fence is signaled yet.
381  * @fence: the fence to check
382  *
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.
387  *
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.
392  *
393  * See also dma_fence_is_signaled_locked().
394  */
395 static inline bool
396 dma_fence_is_signaled(struct dma_fence *fence)
397 {
398         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
399                 return true;
400 
401         if (fence->ops->signaled && fence->ops->signaled(fence)) {
402                 dma_fence_signal(fence);
403                 return true;
404         }
405 
406         return false;
407 }
408 
409 /**
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
413  *
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.
416  */
417 static inline bool __dma_fence_is_later(u32 f1, u32 f2)
418 {
419         return (int)(f1 - f2) > 0;
420 }
421 
422 /**
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
426  *
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.
429  */
430 static inline bool dma_fence_is_later(struct dma_fence *f1,
431                                       struct dma_fence *f2)
432 {
433         if (WARN_ON(f1->context != f2->context))
434                 return false;
435 
436         return __dma_fence_is_later(f1->seqno, f2->seqno);
437 }
438 
439 /**
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
443  *
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.
447  */
448 static inline struct dma_fence *dma_fence_later(struct dma_fence *f1,
449                                                 struct dma_fence *f2)
450 {
451         if (WARN_ON(f1->context != f2->context))
452                 return NULL;
453 
454         /*
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
457          * here is overkill.
458          */
459         if (dma_fence_is_later(f1, f2))
460                 return dma_fence_is_signaled(f1) ? NULL : f1;
461         else
462                 return dma_fence_is_signaled(f2) ? NULL : f2;
463 }
464 
465 /**
466  * dma_fence_get_status_locked - returns the status upon completion
467  * @fence: the dma_fence to query
468  *
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.
474  *
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.
478  */
479 static inline int dma_fence_get_status_locked(struct dma_fence *fence)
480 {
481         if (dma_fence_is_signaled_locked(fence))
482                 return fence->error ?: 1;
483         else
484                 return 0;
485 }
486 
487 int dma_fence_get_status(struct dma_fence *fence);
488 
489 /**
490  * dma_fence_set_error - flag an error condition on the fence
491  * @fence: the dma_fence
492  * @error: the error to store
493  *
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.
499  */
500 static inline void dma_fence_set_error(struct dma_fence *fence,
501                                        int error)
502 {
503         WARN_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
504         WARN_ON(error >= 0 || error < -MAX_ERRNO);
505 
506         fence->error = error;
507 }
508 
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,
512                                        uint32_t count,
513                                        bool intr, signed long timeout,
514                                        uint32_t *idx);
515 
516 /**
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
520  *
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.
524  *
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.
528  *
529  * See also dma_fence_wait_timeout() and dma_fence_wait_any_timeout().
530  */
531 static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
532 {
533         signed long ret;
534 
535         /* Since dma_fence_wait_timeout cannot timeout with
536          * MAX_SCHEDULE_TIMEOUT, only valid return values are
537          * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
538          */
539         ret = dma_fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
540 
541         return ret < 0 ? ret : 0;
542 }
543 
544 u64 dma_fence_context_alloc(unsigned num);
545 
546 #define DMA_FENCE_TRACE(f, fmt, args...) \
547         do {                                                            \
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);    \
552         } while (0)
553 
554 #define DMA_FENCE_WARN(f, fmt, args...) \
555         do {                                                            \
556                 struct dma_fence *__ff = (f);                           \
557                 pr_warn("f %llu#%u: " fmt, __ff->context, __ff->seqno,  \
558                          ##args);                                       \
559         } while (0)
560 
561 #define DMA_FENCE_ERR(f, fmt, args...) \
562         do {                                                            \
563                 struct dma_fence *__ff = (f);                           \
564                 pr_err("f %llu#%u: " fmt, __ff->context, __ff->seqno,   \
565                         ##args);                                        \
566         } while (0)
567 
568 #endif /* __LINUX_DMA_FENCE_H */
569 

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