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 struct list_head child_list; 83 struct list_head active_list; 84}; 85 86enum fence_flag_bits { 87 FENCE_FLAG_SIGNALED_BIT, 88 FENCE_FLAG_ENABLE_SIGNAL_BIT, 89 FENCE_FLAG_USER_BITS, /* must always be last member */ 90}; 91 92typedef void (*fence_func_t)(struct fence *fence, struct fence_cb *cb); 93 94/** 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 98 * 99 * This struct will be initialized by fence_add_callback, additional 100 * data can be passed along by embedding fence_cb in another struct. 101 */ 102struct fence_cb { 103 struct list_head node; 104 fence_func_t func; 105}; 106 107/** 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 119 * as a string 120 * 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). 128 * 129 * This function can be called called from atomic context, but not 130 * from irq context, so normal spinlocks can be used. 131 * 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. 135 * 136 * fence->status may be set in enable_signaling, but only when false is 137 * returned. 138 * 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. 146 * 147 * Notes on signaled: 148 * May set fence->status if returning true. 149 * 150 * Notes on wait: 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. 154 * 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. 160 * 161 * Notes on release: 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. 165 */ 166 167struct fence_ops { 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); 174 175 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); 178}; 179 180void fence_init(struct fence *fence, const struct fence_ops *ops, 181 spinlock_t *lock, unsigned context, unsigned seqno); 182 183void fence_release(struct kref *kref); 184void fence_free(struct fence *fence); 185 186/** 187 * fence_get - increases refcount of the fence 188 * @fence: [in] fence to increase refcount of 189 * 190 * Returns the same fence, with refcount increased by 1. 191 */ 192static inline struct fence *fence_get(struct fence *fence) 193{ 194 if (fence) 195 kref_get(&fence->refcount); 196 return fence; 197} 198 199/** 200 * fence_get_rcu - get a fence from a reservation_object_list with rcu read lock 201 * @fence: [in] fence to increase refcount of 202 * 203 * Function returns NULL if no refcount could be obtained, or the fence. 204 */ 205static inline struct fence *fence_get_rcu(struct fence *fence) 206{ 207 if (kref_get_unless_zero(&fence->refcount)) 208 return fence; 209 else 210 return NULL; 211} 212 213/** 214 * fence_put - decreases refcount of the fence 215 * @fence: [in] fence to reduce refcount of 216 */ 217static inline void fence_put(struct fence *fence) 218{ 219 if (fence) 220 kref_put(&fence->refcount, fence_release); 221} 222 223int fence_signal(struct fence *fence); 224int fence_signal_locked(struct fence *fence); 225signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout); 226int fence_add_callback(struct fence *fence, struct fence_cb *cb, 227 fence_func_t func); 228bool fence_remove_callback(struct fence *fence, struct fence_cb *cb); 229void fence_enable_sw_signaling(struct fence *fence); 230 231/** 232 * fence_is_signaled_locked - Return an indication if the fence is signaled yet. 233 * @fence: [in] the fence to check 234 * 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. 239 * 240 * This function requires fence->lock to be held. 241 */ 242static inline bool 243fence_is_signaled_locked(struct fence *fence) 244{ 245 if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags)) 246 return true; 247 248 if (fence->ops->signaled && fence->ops->signaled(fence)) { 249 fence_signal_locked(fence); 250 return true; 251 } 252 253 return false; 254} 255 256/** 257 * fence_is_signaled - Return an indication if the fence is signaled yet. 258 * @fence: [in] the fence to check 259 * 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. 264 * 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. 269 */ 270static inline bool 271fence_is_signaled(struct fence *fence) 272{ 273 if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags)) 274 return true; 275 276 if (fence->ops->signaled && fence->ops->signaled(fence)) { 277 fence_signal(fence); 278 return true; 279 } 280 281 return false; 282} 283 284/** 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 288 * 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. 291 */ 292static inline bool fence_is_later(struct fence *f1, struct fence *f2) 293{ 294 if (WARN_ON(f1->context != f2->context)) 295 return false; 296 297 return (int)(f1->seqno - f2->seqno) > 0; 298} 299 300/** 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 304 * 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. 308 */ 309static inline struct fence *fence_later(struct fence *f1, struct fence *f2) 310{ 311 if (WARN_ON(f1->context != f2->context)) 312 return NULL; 313 314 /* 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 317 * overkill. 318 */ 319 if (fence_is_later(f1, f2)) 320 return fence_is_signaled(f1) ? NULL : f1; 321 else 322 return fence_is_signaled(f2) ? NULL : f2; 323} 324 325signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout); 326signed long fence_wait_any_timeout(struct fence **fences, uint32_t count, 327 bool intr, signed long timeout); 328 329/** 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 333 * 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. 337 * 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. 341 */ 342static inline signed long fence_wait(struct fence *fence, bool intr) 343{ 344 signed long ret; 345 346 /* Since fence_wait_timeout cannot timeout with 347 * MAX_SCHEDULE_TIMEOUT, only valid return values are 348 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT. 349 */ 350 ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT); 351 352 return ret < 0 ? ret : 0; 353} 354 355unsigned fence_context_alloc(unsigned num); 356 357#define FENCE_TRACE(f, fmt, args...) \ 358 do { \ 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); \ 363 } while (0) 364 365#define FENCE_WARN(f, fmt, args...) \ 366 do { \ 367 struct fence *__ff = (f); \ 368 pr_warn("f %u#%u: " fmt, __ff->context, __ff->seqno, \ 369 ##args); \ 370 } while (0) 371 372#define FENCE_ERR(f, fmt, args...) \ 373 do { \ 374 struct fence *__ff = (f); \ 375 pr_err("f %u#%u: " fmt, __ff->context, __ff->seqno, \ 376 ##args); \ 377 } while (0) 378 379#endif /* __LINUX_FENCE_H */ 380