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 */
fence_get(struct fence * fence)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 */
fence_get_rcu(struct fence * fence)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 */
fence_put(struct fence * fence)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
fence_is_signaled_locked(struct fence * fence)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
fence_is_signaled(struct fence * fence)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 */
fence_later(struct fence * f1,struct fence * f2)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 */
fence_wait(struct fence * fence,bool intr)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