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_FENCE_H
22 #define __LINUX_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 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.
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 * 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.
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.
74 const struct fence_ops
*ops
;
76 struct list_head cb_list
;
78 unsigned context
, seqno
;
82 struct list_head child_list
;
83 struct list_head active_list
;
86 enum fence_flag_bits
{
87 FENCE_FLAG_SIGNALED_BIT
,
88 FENCE_FLAG_ENABLE_SIGNAL_BIT
,
89 FENCE_FLAG_USER_BITS
, /* must always be last member */
92 typedef void (*fence_func_t
)(struct fence
*fence
, struct fence_cb
*cb
);
95 * struct fence_cb - callback for fence_add_callback
96 * @node: used by fence_add_callback to append this struct to fence::cb_list
97 * @func: fence_func_t to call
99 * This struct will be initialized by fence_add_callback, additional
100 * data can be passed along by embedding fence_cb in another struct.
103 struct list_head node
;
108 * struct 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 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->status may be set in enable_signaling, but only when false is
139 * Calling 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 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 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->status if returning true.
151 * Must not be NULL, set to fence_default_wait for default implementation.
152 * the 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.
168 const char * (*get_driver_name
)(struct fence
*fence
);
169 const char * (*get_timeline_name
)(struct fence
*fence
);
170 bool (*enable_signaling
)(struct fence
*fence
);
171 bool (*signaled
)(struct fence
*fence
);
172 signed long (*wait
)(struct fence
*fence
, bool intr
, signed long timeout
);
173 void (*release
)(struct fence
*fence
);
175 int (*fill_driver_data
)(struct fence
*fence
, void *data
, int size
);
176 void (*fence_value_str
)(struct fence
*fence
, char *str
, int size
);
177 void (*timeline_value_str
)(struct fence
*fence
, char *str
, int size
);
180 void fence_init(struct fence
*fence
, const struct fence_ops
*ops
,
181 spinlock_t
*lock
, unsigned context
, unsigned seqno
);
183 void fence_release(struct kref
*kref
);
184 void fence_free(struct fence
*fence
);
187 * fence_get - increases refcount of the fence
188 * @fence: [in] fence to increase refcount of
190 * Returns the same fence, with refcount increased by 1.
192 static inline struct fence
*fence_get(struct fence
*fence
)
195 kref_get(&fence
->refcount
);
200 * fence_get_rcu - get a fence from a reservation_object_list with rcu read lock
201 * @fence: [in] fence to increase refcount of
203 * Function returns NULL if no refcount could be obtained, or the fence.
205 static inline struct fence
*fence_get_rcu(struct fence
*fence
)
207 if (kref_get_unless_zero(&fence
->refcount
))
214 * fence_put - decreases refcount of the fence
215 * @fence: [in] fence to reduce refcount of
217 static inline void fence_put(struct fence
*fence
)
220 kref_put(&fence
->refcount
, fence_release
);
223 int fence_signal(struct fence
*fence
);
224 int fence_signal_locked(struct fence
*fence
);
225 signed long fence_default_wait(struct fence
*fence
, bool intr
, signed long timeout
);
226 int fence_add_callback(struct fence
*fence
, struct fence_cb
*cb
,
228 bool fence_remove_callback(struct fence
*fence
, struct fence_cb
*cb
);
229 void fence_enable_sw_signaling(struct fence
*fence
);
232 * fence_is_signaled_locked - Return an indication if the fence is signaled yet.
233 * @fence: [in] the fence to check
235 * Returns true if the fence was already signaled, false if not. Since this
236 * function doesn't enable signaling, it is not guaranteed to ever return
237 * true if fence_add_callback, fence_wait or fence_enable_sw_signaling
238 * haven't been called before.
240 * This function requires fence->lock to be held.
243 fence_is_signaled_locked(struct fence
*fence
)
245 if (test_bit(FENCE_FLAG_SIGNALED_BIT
, &fence
->flags
))
248 if (fence
->ops
->signaled
&& fence
->ops
->signaled(fence
)) {
249 fence_signal_locked(fence
);
257 * fence_is_signaled - Return an indication if the fence is signaled yet.
258 * @fence: [in] the fence to check
260 * Returns true if the fence was already signaled, false if not. Since this
261 * function doesn't enable signaling, it is not guaranteed to ever return
262 * true if fence_add_callback, fence_wait or fence_enable_sw_signaling
263 * haven't been called before.
265 * It's recommended for seqno fences to call fence_signal when the
266 * operation is complete, it makes it possible to prevent issues from
267 * wraparound between time of issue and time of use by checking the return
268 * value of this function before calling hardware-specific wait instructions.
271 fence_is_signaled(struct fence
*fence
)
273 if (test_bit(FENCE_FLAG_SIGNALED_BIT
, &fence
->flags
))
276 if (fence
->ops
->signaled
&& fence
->ops
->signaled(fence
)) {
285 * fence_is_later - return if f1 is chronologically later than f2
286 * @f1: [in] the first fence from the same context
287 * @f2: [in] the second fence from the same context
289 * Returns true if f1 is chronologically later than f2. Both fences must be
290 * from the same context, since a seqno is not re-used across contexts.
292 static inline bool fence_is_later(struct fence
*f1
, struct fence
*f2
)
294 if (WARN_ON(f1
->context
!= f2
->context
))
297 return (int)(f1
->seqno
- f2
->seqno
) > 0;
301 * fence_later - return the chronologically later fence
302 * @f1: [in] the first fence from the same context
303 * @f2: [in] the second fence from the same context
305 * Returns NULL if both fences are signaled, otherwise the fence that would be
306 * signaled last. Both fences must be from the same context, since a seqno is
307 * not re-used across contexts.
309 static inline struct fence
*fence_later(struct fence
*f1
, struct fence
*f2
)
311 if (WARN_ON(f1
->context
!= f2
->context
))
315 * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been
316 * set if enable_signaling wasn't called, and enabling that here is
319 if (fence_is_later(f1
, f2
))
320 return fence_is_signaled(f1
) ? NULL
: f1
;
322 return fence_is_signaled(f2
) ? NULL
: f2
;
325 signed long fence_wait_timeout(struct fence
*, bool intr
, signed long timeout
);
326 signed long fence_wait_any_timeout(struct fence
**fences
, uint32_t count
,
327 bool intr
, signed long timeout
);
330 * fence_wait - sleep until the fence gets signaled
331 * @fence: [in] the fence to wait on
332 * @intr: [in] if true, do an interruptible wait
334 * This function will return -ERESTARTSYS if interrupted by a signal,
335 * or 0 if the fence was signaled. Other error values may be
336 * returned on custom implementations.
338 * Performs a synchronous wait on this fence. It is assumed the caller
339 * directly or indirectly holds a reference to the fence, otherwise the
340 * fence might be freed before return, resulting in undefined behavior.
342 static inline signed long fence_wait(struct fence
*fence
, bool intr
)
346 /* Since fence_wait_timeout cannot timeout with
347 * MAX_SCHEDULE_TIMEOUT, only valid return values are
348 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
350 ret
= fence_wait_timeout(fence
, intr
, MAX_SCHEDULE_TIMEOUT
);
352 return ret
< 0 ? ret
: 0;
355 unsigned fence_context_alloc(unsigned num
);
357 #define FENCE_TRACE(f, fmt, args...) \
359 struct fence *__ff = (f); \
360 if (config_enabled(CONFIG_FENCE_TRACE)) \
361 pr_info("f %u#%u: " fmt, \
362 __ff->context, __ff->seqno, ##args); \
365 #define FENCE_WARN(f, fmt, args...) \
367 struct fence *__ff = (f); \
368 pr_warn("f %u#%u: " fmt, __ff->context, __ff->seqno, \
372 #define FENCE_ERR(f, fmt, args...) \
374 struct fence *__ff = (f); \
375 pr_err("f %u#%u: " fmt, __ff->context, __ff->seqno, \
379 #endif /* __LINUX_FENCE_H */