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 u64 context; 79 unsigned seqno; 80 unsigned long flags; 81 ktime_t timestamp; 82 int status; 83}; 84 85enum fence_flag_bits { 86 FENCE_FLAG_SIGNALED_BIT, 87 FENCE_FLAG_ENABLE_SIGNAL_BIT, 88 FENCE_FLAG_USER_BITS, /* must always be last member */ 89}; 90 91typedef void (*fence_func_t)(struct fence *fence, struct fence_cb *cb); 92 93/** 94 * struct fence_cb - callback for fence_add_callback 95 * @node: used by fence_add_callback to append this struct to fence::cb_list 96 * @func: fence_func_t to call 97 * 98 * This struct will be initialized by fence_add_callback, additional 99 * data can be passed along by embedding fence_cb in another struct. 100 */ 101struct fence_cb { 102 struct list_head node; 103 fence_func_t func; 104}; 105 106/** 107 * struct fence_ops - operations implemented for fence 108 * @get_driver_name: returns the driver name. 109 * @get_timeline_name: return the name of the context this fence belongs to. 110 * @enable_signaling: enable software signaling of fence. 111 * @signaled: [optional] peek whether the fence is signaled, can be null. 112 * @wait: custom wait implementation, or fence_default_wait. 113 * @release: [optional] called on destruction of fence, can be null 114 * @fill_driver_data: [optional] callback to fill in free-form debug info 115 * Returns amount of bytes filled, or -errno. 116 * @fence_value_str: [optional] fills in the value of the fence as a string 117 * @timeline_value_str: [optional] fills in the current value of the timeline 118 * as a string 119 * 120 * Notes on enable_signaling: 121 * For fence implementations that have the capability for hw->hw 122 * signaling, they can implement this op to enable the necessary 123 * irqs, or insert commands into cmdstream, etc. This is called 124 * in the first wait() or add_callback() path to let the fence 125 * implementation know that there is another driver waiting on 126 * the signal (ie. hw->sw case). 127 * 128 * This function can be called called from atomic context, but not 129 * from irq context, so normal spinlocks can be used. 130 * 131 * A return value of false indicates the fence already passed, 132 * or some failure occurred that made it impossible to enable 133 * signaling. True indicates successful enabling. 134 * 135 * fence->status may be set in enable_signaling, but only when false is 136 * returned. 137 * 138 * Calling fence_signal before enable_signaling is called allows 139 * for a tiny race window in which enable_signaling is called during, 140 * before, or after fence_signal. To fight this, it is recommended 141 * that before enable_signaling returns true an extra reference is 142 * taken on the fence, to be released when the fence is signaled. 143 * This will mean fence_signal will still be called twice, but 144 * the second time will be a noop since it was already signaled. 145 * 146 * Notes on signaled: 147 * May set fence->status if returning true. 148 * 149 * Notes on wait: 150 * Must not be NULL, set to fence_default_wait for default implementation. 151 * the fence_default_wait implementation should work for any fence, as long 152 * as enable_signaling works correctly. 153 * 154 * Must return -ERESTARTSYS if the wait is intr = true and the wait was 155 * interrupted, and remaining jiffies if fence has signaled, or 0 if wait 156 * timed out. Can also return other error values on custom implementations, 157 * which should be treated as if the fence is signaled. For example a hardware 158 * lockup could be reported like that. 159 * 160 * Notes on release: 161 * Can be NULL, this function allows additional commands to run on 162 * destruction of the fence. Can be called from irq context. 163 * If pointer is set to NULL, kfree will get called instead. 164 */ 165 166struct fence_ops { 167 const char * (*get_driver_name)(struct fence *fence); 168 const char * (*get_timeline_name)(struct fence *fence); 169 bool (*enable_signaling)(struct fence *fence); 170 bool (*signaled)(struct fence *fence); 171 signed long (*wait)(struct fence *fence, bool intr, signed long timeout); 172 void (*release)(struct fence *fence); 173 174 int (*fill_driver_data)(struct fence *fence, void *data, int size); 175 void (*fence_value_str)(struct fence *fence, char *str, int size); 176 void (*timeline_value_str)(struct fence *fence, char *str, int size); 177}; 178 179void fence_init(struct fence *fence, const struct fence_ops *ops, 180 spinlock_t *lock, u64 context, unsigned seqno); 181 182void fence_release(struct kref *kref); 183void fence_free(struct fence *fence); 184 185/** 186 * fence_get - increases refcount of the fence 187 * @fence: [in] fence to increase refcount of 188 * 189 * Returns the same fence, with refcount increased by 1. 190 */ 191static inline struct fence *fence_get(struct fence *fence) 192{ 193 if (fence) 194 kref_get(&fence->refcount); 195 return fence; 196} 197 198/** 199 * fence_get_rcu - get a fence from a reservation_object_list with rcu read lock 200 * @fence: [in] fence to increase refcount of 201 * 202 * Function returns NULL if no refcount could be obtained, or the fence. 203 */ 204static inline struct fence *fence_get_rcu(struct fence *fence) 205{ 206 if (kref_get_unless_zero(&fence->refcount)) 207 return fence; 208 else 209 return NULL; 210} 211 212/** 213 * fence_put - decreases refcount of the fence 214 * @fence: [in] fence to reduce refcount of 215 */ 216static inline void fence_put(struct fence *fence) 217{ 218 if (fence) 219 kref_put(&fence->refcount, fence_release); 220} 221 222int fence_signal(struct fence *fence); 223int fence_signal_locked(struct fence *fence); 224signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout); 225int fence_add_callback(struct fence *fence, struct fence_cb *cb, 226 fence_func_t func); 227bool fence_remove_callback(struct fence *fence, struct fence_cb *cb); 228void fence_enable_sw_signaling(struct fence *fence); 229 230/** 231 * fence_is_signaled_locked - Return an indication if the fence is signaled yet. 232 * @fence: [in] the fence to check 233 * 234 * Returns true if the fence was already signaled, false if not. Since this 235 * function doesn't enable signaling, it is not guaranteed to ever return 236 * true if fence_add_callback, fence_wait or fence_enable_sw_signaling 237 * haven't been called before. 238 * 239 * This function requires fence->lock to be held. 240 */ 241static inline bool 242fence_is_signaled_locked(struct fence *fence) 243{ 244 if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags)) 245 return true; 246 247 if (fence->ops->signaled && fence->ops->signaled(fence)) { 248 fence_signal_locked(fence); 249 return true; 250 } 251 252 return false; 253} 254 255/** 256 * fence_is_signaled - Return an indication if the fence is signaled yet. 257 * @fence: [in] the fence to check 258 * 259 * Returns true if the fence was already signaled, false if not. Since this 260 * function doesn't enable signaling, it is not guaranteed to ever return 261 * true if fence_add_callback, fence_wait or fence_enable_sw_signaling 262 * haven't been called before. 263 * 264 * It's recommended for seqno fences to call fence_signal when the 265 * operation is complete, it makes it possible to prevent issues from 266 * wraparound between time of issue and time of use by checking the return 267 * value of this function before calling hardware-specific wait instructions. 268 */ 269static inline bool 270fence_is_signaled(struct fence *fence) 271{ 272 if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags)) 273 return true; 274 275 if (fence->ops->signaled && fence->ops->signaled(fence)) { 276 fence_signal(fence); 277 return true; 278 } 279 280 return false; 281} 282 283/** 284 * fence_is_later - return if f1 is chronologically later than f2 285 * @f1: [in] the first fence from the same context 286 * @f2: [in] the second fence from the same context 287 * 288 * Returns true if f1 is chronologically later than f2. Both fences must be 289 * from the same context, since a seqno is not re-used across contexts. 290 */ 291static inline bool fence_is_later(struct fence *f1, struct fence *f2) 292{ 293 if (WARN_ON(f1->context != f2->context)) 294 return false; 295 296 return (int)(f1->seqno - f2->seqno) > 0; 297} 298 299/** 300 * fence_later - return the chronologically later fence 301 * @f1: [in] the first fence from the same context 302 * @f2: [in] the second fence from the same context 303 * 304 * Returns NULL if both fences are signaled, otherwise the fence that would be 305 * signaled last. Both fences must be from the same context, since a seqno is 306 * not re-used across contexts. 307 */ 308static inline struct fence *fence_later(struct fence *f1, struct fence *f2) 309{ 310 if (WARN_ON(f1->context != f2->context)) 311 return NULL; 312 313 /* 314 * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been 315 * set if enable_signaling wasn't called, and enabling that here is 316 * overkill. 317 */ 318 if (fence_is_later(f1, f2)) 319 return fence_is_signaled(f1) ? NULL : f1; 320 else 321 return fence_is_signaled(f2) ? NULL : f2; 322} 323 324signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout); 325signed long fence_wait_any_timeout(struct fence **fences, uint32_t count, 326 bool intr, signed long timeout); 327 328/** 329 * fence_wait - sleep until the fence gets signaled 330 * @fence: [in] the fence to wait on 331 * @intr: [in] if true, do an interruptible wait 332 * 333 * This function will return -ERESTARTSYS if interrupted by a signal, 334 * or 0 if the fence was signaled. Other error values may be 335 * returned on custom implementations. 336 * 337 * Performs a synchronous wait on this fence. It is assumed the caller 338 * directly or indirectly holds a reference to the fence, otherwise the 339 * fence might be freed before return, resulting in undefined behavior. 340 */ 341static inline signed long fence_wait(struct fence *fence, bool intr) 342{ 343 signed long ret; 344 345 /* Since fence_wait_timeout cannot timeout with 346 * MAX_SCHEDULE_TIMEOUT, only valid return values are 347 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT. 348 */ 349 ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT); 350 351 return ret < 0 ? ret : 0; 352} 353 354u64 fence_context_alloc(unsigned num); 355 356#define FENCE_TRACE(f, fmt, args...) \ 357 do { \ 358 struct fence *__ff = (f); \ 359 if (IS_ENABLED(CONFIG_FENCE_TRACE)) \ 360 pr_info("f %llu#%u: " fmt, \ 361 __ff->context, __ff->seqno, ##args); \ 362 } while (0) 363 364#define FENCE_WARN(f, fmt, args...) \ 365 do { \ 366 struct fence *__ff = (f); \ 367 pr_warn("f %llu#%u: " fmt, __ff->context, __ff->seqno, \ 368 ##args); \ 369 } while (0) 370 371#define FENCE_ERR(f, fmt, args...) \ 372 do { \ 373 struct fence *__ff = (f); \ 374 pr_err("f %llu#%u: " fmt, __ff->context, __ff->seqno, \ 375 ##args); \ 376 } while (0) 377 378#endif /* __LINUX_FENCE_H */ 379