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 33struct fence; 34struct fence_ops; 35struct 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 */ 72struct 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 84enum 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 90typedef 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 */ 100struct 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 165struct 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 178void fence_init(struct fence *fence, const struct fence_ops *ops, 179 spinlock_t *lock, unsigned context, unsigned seqno); 180 181void fence_release(struct kref *kref); 182void 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 */ 190static 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 */ 203static 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 */ 215static inline void fence_put(struct fence *fence) 216{ 217 if (fence) 218 kref_put(&fence->refcount, fence_release); 219} 220 221int fence_signal(struct fence *fence); 222int fence_signal_locked(struct fence *fence); 223signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout); 224int fence_add_callback(struct fence *fence, struct fence_cb *cb, 225 fence_func_t func); 226bool fence_remove_callback(struct fence *fence, struct fence_cb *cb); 227void 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 */ 240static inline bool 241fence_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 */ 268static inline bool 269fence_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_is_later - return if f1 is chronologically later than f2 284 * @f1: [in] the first fence from the same context 285 * @f2: [in] the second fence from the same context 286 * 287 * Returns true if f1 is chronologically later than f2. Both fences must be 288 * from the same context, since a seqno is not re-used across contexts. 289 */ 290static inline bool fence_is_later(struct fence *f1, struct fence *f2) 291{ 292 if (WARN_ON(f1->context != f2->context)) 293 return false; 294 295 return f1->seqno - f2->seqno < INT_MAX; 296} 297 298/** 299 * fence_later - return the chronologically later fence 300 * @f1: [in] the first fence from the same context 301 * @f2: [in] the second fence from the same context 302 * 303 * Returns NULL if both fences are signaled, otherwise the fence that would be 304 * signaled last. Both fences must be from the same context, since a seqno is 305 * not re-used across contexts. 306 */ 307static inline struct fence *fence_later(struct fence *f1, struct fence *f2) 308{ 309 if (WARN_ON(f1->context != f2->context)) 310 return NULL; 311 312 /* 313 * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been 314 * set if enable_signaling wasn't called, and enabling that here is 315 * overkill. 316 */ 317 if (fence_is_later(f1, f2)) 318 return fence_is_signaled(f1) ? NULL : f1; 319 else 320 return fence_is_signaled(f2) ? NULL : f2; 321} 322 323signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout); 324signed long fence_wait_any_timeout(struct fence **fences, uint32_t count, 325 bool intr, signed long timeout); 326 327/** 328 * fence_wait - sleep until the fence gets signaled 329 * @fence: [in] the fence to wait on 330 * @intr: [in] if true, do an interruptible wait 331 * 332 * This function will return -ERESTARTSYS if interrupted by a signal, 333 * or 0 if the fence was signaled. Other error values may be 334 * returned on custom implementations. 335 * 336 * Performs a synchronous wait on this fence. It is assumed the caller 337 * directly or indirectly holds a reference to the fence, otherwise the 338 * fence might be freed before return, resulting in undefined behavior. 339 */ 340static inline signed long fence_wait(struct fence *fence, bool intr) 341{ 342 signed long ret; 343 344 /* Since fence_wait_timeout cannot timeout with 345 * MAX_SCHEDULE_TIMEOUT, only valid return values are 346 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT. 347 */ 348 ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT); 349 350 return ret < 0 ? ret : 0; 351} 352 353unsigned fence_context_alloc(unsigned num); 354 355#define FENCE_TRACE(f, fmt, args...) \ 356 do { \ 357 struct fence *__ff = (f); \ 358 if (config_enabled(CONFIG_FENCE_TRACE)) \ 359 pr_info("f %u#%u: " fmt, \ 360 __ff->context, __ff->seqno, ##args); \ 361 } while (0) 362 363#define FENCE_WARN(f, fmt, args...) \ 364 do { \ 365 struct fence *__ff = (f); \ 366 pr_warn("f %u#%u: " fmt, __ff->context, __ff->seqno, \ 367 ##args); \ 368 } while (0) 369 370#define FENCE_ERR(f, fmt, args...) \ 371 do { \ 372 struct fence *__ff = (f); \ 373 pr_err("f %u#%u: " fmt, __ff->context, __ff->seqno, \ 374 ##args); \ 375 } while (0) 376 377#endif /* __LINUX_FENCE_H */ 378