include/linux/fence.h

   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
  32 struct fence;
  33 struct fence_ops;
  34 struct fence_cb;
  35
  36 /**
  37  * struct fence - software synchronization primitive
  38  * @refcount: refcount for this fence
  39  * @ops: fence_ops associated with this fence
  40  * @cb_list: list of all callbacks to call
  41  * @lock: spin_lock_irqsave used for locking
  42  * @context: execution context this fence belongs to, returned by
  43  *           fence_context_alloc()
  44  * @seqno: the sequence number of this fence inside the execution context,
  45  * can be compared to decide which fence would be signaled later.
  46  * @flags: A mask of FENCE_FLAG_* defined below
  47  * @timestamp: Timestamp when the fence was signaled.
  48  * @status: Optional, only valid if < 0, must be set before calling
  49  * fence_signal, indicates that the fence has completed with an error.
  50  *
  51  * the flags member must be manipulated and read using the appropriate
  52  * atomic ops (bit_*), so taking the spinlock will not be needed most
  53  * of the time.
  54  *
  55  * FENCE_FLAG_SIGNALED_BIT - fence is already signaled
  56  * FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called*
  57  * FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
  58  * implementer of the fence for its own purposes. Can be used in different
  59  * ways by different fence implementers, so do not rely on this.
  60  *
  61  * *) Since atomic bitops are used, this is not guaranteed to be the case.
  62  * Particularly, if the bit was set, but fence_signal was called right
  63  * before this bit was set, it would have been able to set the
  64  * FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
  65  * Adding a check for FENCE_FLAG_SIGNALED_BIT after setting
  66  * FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
  67  * after fence_signal was called, any enable_signaling call will have either
  68  * been completed, or never called at all.
  69  */
  70 struct fence {
  71         struct kref refcount;
  72         const struct fence_ops *ops;
  73         struct list_head cb_list;
  74         spinlock_t *lock;
  75         unsigned context, seqno;
  76         unsigned long flags;
  77         ktime_t timestamp;
  78         int status;
  79 };
  80
  81 enum fence_flag_bits {
  82         FENCE_FLAG_SIGNALED_BIT,
  83         FENCE_FLAG_ENABLE_SIGNAL_BIT,
  84         FENCE_FLAG_USER_BITS, /* must always be last member */
  85 };
  86
  87 typedef void (*fence_func_t)(struct fence *fence, struct fence_cb *cb);
  88
  89 /**
  90  * struct fence_cb - callback for fence_add_callback
  91  * @node: used by fence_add_callback to append this struct to fence::cb_list
  92  * @func: fence_func_t to call
  93  *
  94  * This struct will be initialized by fence_add_callback, additional
  95  * data can be passed along by embedding fence_cb in another struct.
  96  */
  97 struct fence_cb {
  98         struct list_head node;
  99         fence_func_t func;
 100 };
 101
 102 /**
 103  * struct fence_ops - operations implemented for fence
 104  * @get_driver_name: returns the driver name.
 105  * @get_timeline_name: return the name of the context this fence belongs to.
 106  * @enable_signaling: enable software signaling of fence.
 107  * @signaled: [optional] peek whether the fence is signaled, can be null.
 108  * @wait: custom wait implementation, or fence_default_wait.
 109  * @release: [optional] called on destruction of fence, can be null
 110  * @fill_driver_data: [optional] callback to fill in free-form debug info
 111  * Returns amount of bytes filled, or -errno.
 112  * @fence_value_str: [optional] fills in the value of the fence as a string
 113  * @timeline_value_str: [optional] fills in the current value of the timeline
 114  * as a string
 115  *
 116  * Notes on enable_signaling:
 117  * For fence implementations that have the capability for hw->hw
 118  * signaling, they can implement this op to enable the necessary
 119  * irqs, or insert commands into cmdstream, etc.  This is called
 120  * in the first wait() or add_callback() path to let the fence
 121  * implementation know that there is another driver waiting on
 122  * the signal (ie. hw->sw case).
 123  *
 124  * This function can be called called from atomic context, but not
 125  * from irq context, so normal spinlocks can be used.
 126  *
 127  * A return value of false indicates the fence already passed,
 128  * or some failure occured that made it impossible to enable
 129  * signaling. True indicates succesful enabling.
 130  *
 131  * fence->status may be set in enable_signaling, but only when false is
 132  * returned.
 133  *
 134  * Calling fence_signal before enable_signaling is called allows
 135  * for a tiny race window in which enable_signaling is called during,
 136  * before, or after fence_signal. To fight this, it is recommended
 137  * that before enable_signaling returns true an extra reference is
 138  * taken on the fence, to be released when the fence is signaled.
 139  * This will mean fence_signal will still be called twice, but
 140  * the second time will be a noop since it was already signaled.
 141  *
 142  * Notes on signaled:
 143  * May set fence->status if returning true.
 144  *
 145  * Notes on wait:
 146  * Must not be NULL, set to fence_default_wait for default implementation.
 147  * the fence_default_wait implementation should work for any fence, as long
 148  * as enable_signaling works correctly.
 149  *
 150  * Must return -ERESTARTSYS if the wait is intr = true and the wait was
 151  * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
 152  * timed out. Can also return other error values on custom implementations,
 153  * which should be treated as if the fence is signaled. For example a hardware
 154  * lockup could be reported like that.
 155  *
 156  * Notes on release:
 157  * Can be NULL, this function allows additional commands to run on
 158  * destruction of the fence. Can be called from irq context.
 159  * If pointer is set to NULL, kfree will get called instead.
 160  */
 161
 162 struct fence_ops {
 163         const char * (*get_driver_name)(struct fence *fence);
 164         const char * (*get_timeline_name)(struct fence *fence);
 165         bool (*enable_signaling)(struct fence *fence);
 166         bool (*signaled)(struct fence *fence);
 167         signed long (*wait)(struct fence *fence, bool intr, signed long timeout);
 168         void (*release)(struct fence *fence);
 169
 170         int (*fill_driver_data)(struct fence *fence, void *data, int size);
 171         void (*fence_value_str)(struct fence *fence, char *str, int size);
 172         void (*timeline_value_str)(struct fence *fence, char *str, int size);
 173 };
 174
 175 void fence_init(struct fence *fence, const struct fence_ops *ops,
 176                 spinlock_t *lock, unsigned context, unsigned seqno);
 177
 178 void fence_release(struct kref *kref);
 179 void fence_free(struct fence *fence);
 180
 181 /**
 182  * fence_get - increases refcount of the fence
 183  * @fence:      [in]    fence to increase refcount of
 184  *
 185  * Returns the same fence, with refcount increased by 1.
 186  */
 187 static inline struct fence *fence_get(struct fence *fence)
 188 {
 189         if (fence)
 190                 kref_get(&fence->refcount);
 191         return fence;
 192 }
 193
 194 /**
 195  * fence_put - decreases refcount of the fence
 196  * @fence:      [in]    fence to reduce refcount of
 197  */
 198 static inline void fence_put(struct fence *fence)
 199 {
 200         if (fence)
 201                 kref_put(&fence->refcount, fence_release);
 202 }
 203
 204 int fence_signal(struct fence *fence);
 205 int fence_signal_locked(struct fence *fence);
 206 signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout);
 207 int fence_add_callback(struct fence *fence, struct fence_cb *cb,
 208                        fence_func_t func);
 209 bool fence_remove_callback(struct fence *fence, struct fence_cb *cb);
 210 void fence_enable_sw_signaling(struct fence *fence);
 211
 212 /**
 213  * fence_is_signaled_locked - Return an indication if the fence is signaled yet.
 214  * @fence:      [in]    the fence to check
 215  *
 216  * Returns true if the fence was already signaled, false if not. Since this
 217  * function doesn't enable signaling, it is not guaranteed to ever return
 218  * true if fence_add_callback, fence_wait or fence_enable_sw_signaling
 219  * haven't been called before.
 220  *
 221  * This function requires fence->lock to be held.
 222  */
 223 static inline bool
 224 fence_is_signaled_locked(struct fence *fence)
 225 {
 226         if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 227                 return true;
 228
 229         if (fence->ops->signaled && fence->ops->signaled(fence)) {
 230                 fence_signal_locked(fence);
 231                 return true;
 232         }
 233
 234         return false;
 235 }
 236
 237 /**
 238  * fence_is_signaled - Return an indication if the fence is signaled yet.
 239  * @fence:      [in]    the fence to check
 240  *
 241  * Returns true if the fence was already signaled, false if not. Since this
 242  * function doesn't enable signaling, it is not guaranteed to ever return
 243  * true if fence_add_callback, fence_wait or fence_enable_sw_signaling
 244  * haven't been called before.
 245  *
 246  * It's recommended for seqno fences to call fence_signal when the
 247  * operation is complete, it makes it possible to prevent issues from
 248  * wraparound between time of issue and time of use by checking the return
 249  * value of this function before calling hardware-specific wait instructions.
 250  */
 251 static inline bool
 252 fence_is_signaled(struct fence *fence)
 253 {
 254         if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 255                 return true;
 256
 257         if (fence->ops->signaled && fence->ops->signaled(fence)) {
 258                 fence_signal(fence);
 259                 return true;
 260         }
 261
 262         return false;
 263 }
 264
 265 /**
 266  * fence_later - return the chronologically later fence
 267  * @f1: [in]    the first fence from the same context
 268  * @f2: [in]    the second fence from the same context
 269  *
 270  * Returns NULL if both fences are signaled, otherwise the fence that would be
 271  * signaled last. Both fences must be from the same context, since a seqno is
 272  * not re-used across contexts.
 273  */
 274 static inline struct fence *fence_later(struct fence *f1, struct fence *f2)
 275 {
 276         if (WARN_ON(f1->context != f2->context))
 277                 return NULL;
 278
 279         /*
 280          * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been
 281          * set if enable_signaling wasn't called, and enabling that here is
 282          * overkill.
 283          */
 284         if (f2->seqno - f1->seqno <= INT_MAX)
 285                 return fence_is_signaled(f2) ? NULL : f2;
 286         else
 287                 return fence_is_signaled(f1) ? NULL : f1;
 288 }
 289
 290 signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout);
 291
 292
 293 /**
 294  * fence_wait - sleep until the fence gets signaled
 295  * @fence:      [in]    the fence to wait on
 296  * @intr:       [in]    if true, do an interruptible wait
 297  *
 298  * This function will return -ERESTARTSYS if interrupted by a signal,
 299  * or 0 if the fence was signaled. Other error values may be
 300  * returned on custom implementations.
 301  *
 302  * Performs a synchronous wait on this fence. It is assumed the caller
 303  * directly or indirectly holds a reference to the fence, otherwise the
 304  * fence might be freed before return, resulting in undefined behavior.
 305  */
 306 static inline signed long fence_wait(struct fence *fence, bool intr)
 307 {
 308         signed long ret;
 309
 310         /* Since fence_wait_timeout cannot timeout with
 311          * MAX_SCHEDULE_TIMEOUT, only valid return values are
 312          * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
 313          */
 314         ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
 315
 316         return ret < 0 ? ret : 0;
 317 }
 318
 319 unsigned fence_context_alloc(unsigned num);
 320
 321 #define FENCE_TRACE(f, fmt, args...) \
 322         do {                                                            \
 323                 struct fence *__ff = (f);                               \
 324                 if (config_enabled(CONFIG_FENCE_TRACE))                 \
 325                         pr_info("f %u#%u: " fmt,                        \
 326                                 __ff->context, __ff->seqno, ##args);    \
 327         } while (0)
 328
 329 #define FENCE_WARN(f, fmt, args...) \
 330         do {                                                            \
 331                 struct fence *__ff = (f);                               \
 332                 pr_warn("f %u#%u: " fmt, __ff->context, __ff->seqno,    \
 333                          ##args);                                       \
 334         } while (0)
 335
 336 #define FENCE_ERR(f, fmt, args...) \
 337         do {                                                            \
 338                 struct fence *__ff = (f);                               \
 339                 pr_err("f %u#%u: " fmt, __ff->context, __ff->seqno,     \
 340                         ##args);                                        \
 341         } while (0)
 342
 343 #endif /* __LINUX_FENCE_H */