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TOMOYO Linux Cross Reference
Linux/include/linux/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_FENCE_H
 22 #define __LINUX_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 fence;
 34 struct fence_ops;
 35 struct fence_cb;
 36 
 37 /**
 38  * struct fence - software synchronization primitive
 39  * @refcount: refcount for this fence
 40  * @ops: 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  *           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 FENCE_FLAG_* defined below
 49  * @timestamp: Timestamp when the fence was signaled.
 50  * @status: Optional, only valid if < 0, must be set before calling
 51  * 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  * FENCE_FLAG_SIGNALED_BIT - fence is already signaled
 58  * FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called*
 59  * 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.
 62  *
 63  * *) Since atomic bitops are used, this is not guaranteed to be the case.
 64  * Particularly, if the bit was set, but fence_signal was called right
 65  * before this bit was set, it would have been able to set the
 66  * FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
 67  * Adding a check for FENCE_FLAG_SIGNALED_BIT after setting
 68  * FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
 69  * after fence_signal was called, any enable_signaling call will have either
 70  * been completed, or never called at all.
 71  */
 72 struct fence {
 73         struct kref refcount;
 74         const struct fence_ops *ops;
 75         struct rcu_head rcu;
 76         struct list_head cb_list;
 77         spinlock_t *lock;
 78         unsigned context, seqno;
 79         unsigned long flags;
 80         ktime_t timestamp;
 81         int status;
 82 };
 83 
 84 enum fence_flag_bits {
 85         FENCE_FLAG_SIGNALED_BIT,
 86         FENCE_FLAG_ENABLE_SIGNAL_BIT,
 87         FENCE_FLAG_USER_BITS, /* must always be last member */
 88 };
 89 
 90 typedef void (*fence_func_t)(struct fence *fence, struct fence_cb *cb);
 91 
 92 /**
 93  * struct fence_cb - callback for fence_add_callback
 94  * @node: used by fence_add_callback to append this struct to fence::cb_list
 95  * @func: fence_func_t to call
 96  *
 97  * This struct will be initialized by fence_add_callback, additional
 98  * data can be passed along by embedding fence_cb in another struct.
 99  */
100 struct fence_cb {
101         struct list_head node;
102         fence_func_t func;
103 };
104 
105 /**
106  * struct fence_ops - operations implemented for fence
107  * @get_driver_name: returns the driver name.
108  * @get_timeline_name: return the name of the context this fence belongs to.
109  * @enable_signaling: enable software signaling of fence.
110  * @signaled: [optional] peek whether the fence is signaled, can be null.
111  * @wait: custom wait implementation, or fence_default_wait.
112  * @release: [optional] called on destruction of fence, can be null
113  * @fill_driver_data: [optional] callback to fill in free-form debug info
114  * Returns amount of bytes filled, or -errno.
115  * @fence_value_str: [optional] fills in the value of the fence as a string
116  * @timeline_value_str: [optional] fills in the current value of the timeline
117  * as a string
118  *
119  * Notes on enable_signaling:
120  * For fence implementations that have the capability for hw->hw
121  * signaling, they can implement this op to enable the necessary
122  * irqs, or insert commands into cmdstream, etc.  This is called
123  * in the first wait() or add_callback() path to let the fence
124  * implementation know that there is another driver waiting on
125  * the signal (ie. hw->sw case).
126  *
127  * This function can be called called from atomic context, but not
128  * from irq context, so normal spinlocks can be used.
129  *
130  * A return value of false indicates the fence already passed,
131  * or some failure occurred that made it impossible to enable
132  * signaling. True indicates successful enabling.
133  *
134  * fence->status may be set in enable_signaling, but only when false is
135  * returned.
136  *
137  * Calling fence_signal before enable_signaling is called allows
138  * for a tiny race window in which enable_signaling is called during,
139  * before, or after fence_signal. To fight this, it is recommended
140  * that before enable_signaling returns true an extra reference is
141  * taken on the fence, to be released when the fence is signaled.
142  * This will mean fence_signal will still be called twice, but
143  * the second time will be a noop since it was already signaled.
144  *
145  * Notes on signaled:
146  * May set fence->status if returning true.
147  *
148  * Notes on wait:
149  * Must not be NULL, set to fence_default_wait for default implementation.
150  * the fence_default_wait implementation should work for any fence, as long
151  * as enable_signaling works correctly.
152  *
153  * Must return -ERESTARTSYS if the wait is intr = true and the wait was
154  * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
155  * timed out. Can also return other error values on custom implementations,
156  * which should be treated as if the fence is signaled. For example a hardware
157  * lockup could be reported like that.
158  *
159  * Notes on release:
160  * Can be NULL, this function allows additional commands to run on
161  * destruction of the fence. Can be called from irq context.
162  * If pointer is set to NULL, kfree will get called instead.
163  */
164 
165 struct fence_ops {
166         const char * (*get_driver_name)(struct fence *fence);
167         const char * (*get_timeline_name)(struct fence *fence);
168         bool (*enable_signaling)(struct fence *fence);
169         bool (*signaled)(struct fence *fence);
170         signed long (*wait)(struct fence *fence, bool intr, signed long timeout);
171         void (*release)(struct fence *fence);
172 
173         int (*fill_driver_data)(struct fence *fence, void *data, int size);
174         void (*fence_value_str)(struct fence *fence, char *str, int size);
175         void (*timeline_value_str)(struct fence *fence, char *str, int size);
176 };
177 
178 void fence_init(struct fence *fence, const struct fence_ops *ops,
179                 spinlock_t *lock, unsigned context, unsigned seqno);
180 
181 void fence_release(struct kref *kref);
182 void fence_free(struct fence *fence);
183 
184 /**
185  * fence_get - increases refcount of the fence
186  * @fence:      [in]    fence to increase refcount of
187  *
188  * Returns the same fence, with refcount increased by 1.
189  */
190 static inline struct fence *fence_get(struct fence *fence)
191 {
192         if (fence)
193                 kref_get(&fence->refcount);
194         return fence;
195 }
196 
197 /**
198  * fence_get_rcu - get a fence from a reservation_object_list with rcu read lock
199  * @fence:      [in]    fence to increase refcount of
200  *
201  * Function returns NULL if no refcount could be obtained, or the fence.
202  */
203 static inline struct fence *fence_get_rcu(struct fence *fence)
204 {
205         if (kref_get_unless_zero(&fence->refcount))
206                 return fence;
207         else
208                 return NULL;
209 }
210 
211 /**
212  * fence_put - decreases refcount of the fence
213  * @fence:      [in]    fence to reduce refcount of
214  */
215 static inline void fence_put(struct fence *fence)
216 {
217         if (fence)
218                 kref_put(&fence->refcount, fence_release);
219 }
220 
221 int fence_signal(struct fence *fence);
222 int fence_signal_locked(struct fence *fence);
223 signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout);
224 int fence_add_callback(struct fence *fence, struct fence_cb *cb,
225                        fence_func_t func);
226 bool fence_remove_callback(struct fence *fence, struct fence_cb *cb);
227 void fence_enable_sw_signaling(struct fence *fence);
228 
229 /**
230  * fence_is_signaled_locked - Return an indication if the fence is signaled yet.
231  * @fence:      [in]    the fence to check
232  *
233  * Returns true if the fence was already signaled, false if not. Since this
234  * function doesn't enable signaling, it is not guaranteed to ever return
235  * true if fence_add_callback, fence_wait or fence_enable_sw_signaling
236  * haven't been called before.
237  *
238  * This function requires fence->lock to be held.
239  */
240 static inline bool
241 fence_is_signaled_locked(struct fence *fence)
242 {
243         if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
244                 return true;
245 
246         if (fence->ops->signaled && fence->ops->signaled(fence)) {
247                 fence_signal_locked(fence);
248                 return true;
249         }
250 
251         return false;
252 }
253 
254 /**
255  * fence_is_signaled - Return an indication if the fence is signaled yet.
256  * @fence:      [in]    the fence to check
257  *
258  * Returns true if the fence was already signaled, false if not. Since this
259  * function doesn't enable signaling, it is not guaranteed to ever return
260  * true if fence_add_callback, fence_wait or fence_enable_sw_signaling
261  * haven't been called before.
262  *
263  * It's recommended for seqno fences to call fence_signal when the
264  * operation is complete, it makes it possible to prevent issues from
265  * wraparound between time of issue and time of use by checking the return
266  * value of this function before calling hardware-specific wait instructions.
267  */
268 static inline bool
269 fence_is_signaled(struct fence *fence)
270 {
271         if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
272                 return true;
273 
274         if (fence->ops->signaled && fence->ops->signaled(fence)) {
275                 fence_signal(fence);
276                 return true;
277         }
278 
279         return false;
280 }
281 
282 /**
283  * fence_later - return the chronologically later fence
284  * @f1: [in]    the first fence from the same context
285  * @f2: [in]    the second fence from the same context
286  *
287  * Returns NULL if both fences are signaled, otherwise the fence that would be
288  * signaled last. Both fences must be from the same context, since a seqno is
289  * not re-used across contexts.
290  */
291 static inline struct fence *fence_later(struct fence *f1, struct fence *f2)
292 {
293         if (WARN_ON(f1->context != f2->context))
294                 return NULL;
295 
296         /*
297          * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been
298          * set if enable_signaling wasn't called, and enabling that here is
299          * overkill.
300          */
301         if (f2->seqno - f1->seqno <= INT_MAX)
302                 return fence_is_signaled(f2) ? NULL : f2;
303         else
304                 return fence_is_signaled(f1) ? NULL : f1;
305 }
306 
307 signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout);
308 
309 
310 /**
311  * fence_wait - sleep until the fence gets signaled
312  * @fence:      [in]    the fence to wait on
313  * @intr:       [in]    if true, do an interruptible wait
314  *
315  * This function will return -ERESTARTSYS if interrupted by a signal,
316  * or 0 if the fence was signaled. Other error values may be
317  * returned on custom implementations.
318  *
319  * Performs a synchronous wait on this fence. It is assumed the caller
320  * directly or indirectly holds a reference to the fence, otherwise the
321  * fence might be freed before return, resulting in undefined behavior.
322  */
323 static inline signed long fence_wait(struct fence *fence, bool intr)
324 {
325         signed long ret;
326 
327         /* Since fence_wait_timeout cannot timeout with
328          * MAX_SCHEDULE_TIMEOUT, only valid return values are
329          * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
330          */
331         ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
332 
333         return ret < 0 ? ret : 0;
334 }
335 
336 unsigned fence_context_alloc(unsigned num);
337 
338 #define FENCE_TRACE(f, fmt, args...) \
339         do {                                                            \
340                 struct fence *__ff = (f);                               \
341                 if (config_enabled(CONFIG_FENCE_TRACE))                 \
342                         pr_info("f %u#%u: " fmt,                        \
343                                 __ff->context, __ff->seqno, ##args);    \
344         } while (0)
345 
346 #define FENCE_WARN(f, fmt, args...) \
347         do {                                                            \
348                 struct fence *__ff = (f);                               \
349                 pr_warn("f %u#%u: " fmt, __ff->context, __ff->seqno,    \
350                          ##args);                                       \
351         } while (0)
352 
353 #define FENCE_ERR(f, fmt, args...) \
354         do {                                                            \
355                 struct fence *__ff = (f);                               \
356                 pr_err("f %u#%u: " fmt, __ff->context, __ff->seqno,     \
357                         ##args);                                        \
358         } while (0)
359 
360 #endif /* __LINUX_FENCE_H */
361 

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