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 #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  * @child_list: list of children fences
  53  * @active_list: list of active fences
  54  *
  55  * the flags member must be manipulated and read using the appropriate
  56  * atomic ops (bit_*), so taking the spinlock will not be needed most
  57  * of the time.
  58  *
  59  * FENCE_FLAG_SIGNALED_BIT - fence is already signaled
  60  * FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called*
  61  * FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
  62  * implementer of the fence for its own purposes. Can be used in different
  63  * ways by different fence implementers, so do not rely on this.
  64  *
  65  * *) Since atomic bitops are used, this is not guaranteed to be the case.
  66  * Particularly, if the bit was set, but fence_signal was called right
  67  * before this bit was set, it would have been able to set the
  68  * FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.
  69  * Adding a check for FENCE_FLAG_SIGNALED_BIT after setting
  70  * FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that
  71  * after fence_signal was called, any enable_signaling call will have either
  72  * been completed, or never called at all.
  73  */
  74 struct fence {
  75         struct kref refcount;
  76         const struct fence_ops *ops;
  77         struct rcu_head rcu;
  78         struct list_head cb_list;
  79         spinlock_t *lock;
  80         u64 context;
  81         unsigned seqno;
  82         unsigned long flags;
  83         ktime_t timestamp;
  84         int status;
  85 };
  86
  87 enum fence_flag_bits {
  88         FENCE_FLAG_SIGNALED_BIT,
  89         FENCE_FLAG_ENABLE_SIGNAL_BIT,
  90         FENCE_FLAG_USER_BITS, /* must always be last member */
  91 };
  92
  93 typedef void (*fence_func_t)(struct fence *fence, struct fence_cb *cb);
  94
  95 /**
  96  * struct fence_cb - callback for fence_add_callback
  97  * @node: used by fence_add_callback to append this struct to fence::cb_list
  98  * @func: fence_func_t to call
  99  *
 100  * This struct will be initialized by fence_add_callback, additional
 101  * data can be passed along by embedding fence_cb in another struct.
 102  */
 103 struct fence_cb {
 104         struct list_head node;
 105         fence_func_t func;
 106 };
 107
 108 /**
 109  * struct fence_ops - operations implemented for fence
 110  * @get_driver_name: returns the driver name.
 111  * @get_timeline_name: return the name of the context this fence belongs to.
 112  * @enable_signaling: enable software signaling of fence.
 113  * @signaled: [optional] peek whether the fence is signaled, can be null.
 114  * @wait: custom wait implementation, or fence_default_wait.
 115  * @release: [optional] called on destruction of fence, can be null
 116  * @fill_driver_data: [optional] callback to fill in free-form debug info
 117  * Returns amount of bytes filled, or -errno.
 118  * @fence_value_str: [optional] fills in the value of the fence as a string
 119  * @timeline_value_str: [optional] fills in the current value of the timeline
 120  * as a string
 121  *
 122  * Notes on enable_signaling:
 123  * For fence implementations that have the capability for hw->hw
 124  * signaling, they can implement this op to enable the necessary
 125  * irqs, or insert commands into cmdstream, etc.  This is called
 126  * in the first wait() or add_callback() path to let the fence
 127  * implementation know that there is another driver waiting on
 128  * the signal (ie. hw->sw case).
 129  *
 130  * This function can be called called from atomic context, but not
 131  * from irq context, so normal spinlocks can be used.
 132  *
 133  * A return value of false indicates the fence already passed,
 134  * or some failure occurred that made it impossible to enable
 135  * signaling. True indicates successful enabling.
 136  *
 137  * fence->status may be set in enable_signaling, but only when false is
 138  * returned.
 139  *
 140  * Calling fence_signal before enable_signaling is called allows
 141  * for a tiny race window in which enable_signaling is called during,
 142  * before, or after fence_signal. To fight this, it is recommended
 143  * that before enable_signaling returns true an extra reference is
 144  * taken on the fence, to be released when the fence is signaled.
 145  * This will mean fence_signal will still be called twice, but
 146  * the second time will be a noop since it was already signaled.
 147  *
 148  * Notes on signaled:
 149  * May set fence->status if returning true.
 150  *
 151  * Notes on wait:
 152  * Must not be NULL, set to fence_default_wait for default implementation.
 153  * the fence_default_wait implementation should work for any fence, as long
 154  * as enable_signaling works correctly.
 155  *
 156  * Must return -ERESTARTSYS if the wait is intr = true and the wait was
 157  * interrupted, and remaining jiffies if fence has signaled, or 0 if wait
 158  * timed out. Can also return other error values on custom implementations,
 159  * which should be treated as if the fence is signaled. For example a hardware
 160  * lockup could be reported like that.
 161  *
 162  * Notes on release:
 163  * Can be NULL, this function allows additional commands to run on
 164  * destruction of the fence. Can be called from irq context.
 165  * If pointer is set to NULL, kfree will get called instead.
 166  */
 167
 168 struct fence_ops {
 169         const char * (*get_driver_name)(struct fence *fence);
 170         const char * (*get_timeline_name)(struct fence *fence);
 171         bool (*enable_signaling)(struct fence *fence);
 172         bool (*signaled)(struct fence *fence);
 173         signed long (*wait)(struct fence *fence, bool intr, signed long timeout);
 174         void (*release)(struct fence *fence);
 175
 176         int (*fill_driver_data)(struct fence *fence, void *data, int size);
 177         void (*fence_value_str)(struct fence *fence, char *str, int size);
 178         void (*timeline_value_str)(struct fence *fence, char *str, int size);
 179 };
 180
 181 void fence_init(struct fence *fence, const struct fence_ops *ops,
 182                 spinlock_t *lock, u64 context, unsigned seqno);
 183
 184 void fence_release(struct kref *kref);
 185 void fence_free(struct fence *fence);
 186
 187 /**
 188  * fence_get - increases refcount of the fence
 189  * @fence:      [in]    fence to increase refcount of
 190  *
 191  * Returns the same fence, with refcount increased by 1.
 192  */
 193 static inline struct fence *fence_get(struct fence *fence)
 194 {
 195         if (fence)
 196                 kref_get(&fence->refcount);
 197         return fence;
 198 }
 199
 200 /**
 201  * fence_get_rcu - get a fence from a reservation_object_list with rcu read lock
 202  * @fence:      [in]    fence to increase refcount of
 203  *
 204  * Function returns NULL if no refcount could be obtained, or the fence.
 205  */
 206 static inline struct fence *fence_get_rcu(struct fence *fence)
 207 {
 208         if (kref_get_unless_zero(&fence->refcount))
 209                 return fence;
 210         else
 211                 return NULL;
 212 }
 213
 214 /**
 215  * fence_put - decreases refcount of the fence
 216  * @fence:      [in]    fence to reduce refcount of
 217  */
 218 static inline void fence_put(struct fence *fence)
 219 {
 220         if (fence)
 221                 kref_put(&fence->refcount, fence_release);
 222 }
 223
 224 int fence_signal(struct fence *fence);
 225 int fence_signal_locked(struct fence *fence);
 226 signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout);
 227 int fence_add_callback(struct fence *fence, struct fence_cb *cb,
 228                        fence_func_t func);
 229 bool fence_remove_callback(struct fence *fence, struct fence_cb *cb);
 230 void fence_enable_sw_signaling(struct fence *fence);
 231
 232 /**
 233  * fence_is_signaled_locked - Return an indication if the fence is signaled yet.
 234  * @fence:      [in]    the fence to check
 235  *
 236  * Returns true if the fence was already signaled, false if not. Since this
 237  * function doesn't enable signaling, it is not guaranteed to ever return
 238  * true if fence_add_callback, fence_wait or fence_enable_sw_signaling
 239  * haven't been called before.
 240  *
 241  * This function requires fence->lock to be held.
 242  */
 243 static inline bool
 244 fence_is_signaled_locked(struct fence *fence)
 245 {
 246         if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 247                 return true;
 248
 249         if (fence->ops->signaled && fence->ops->signaled(fence)) {
 250                 fence_signal_locked(fence);
 251                 return true;
 252         }
 253
 254         return false;
 255 }
 256
 257 /**
 258  * fence_is_signaled - Return an indication if the fence is signaled yet.
 259  * @fence:      [in]    the fence to check
 260  *
 261  * Returns true if the fence was already signaled, false if not. Since this
 262  * function doesn't enable signaling, it is not guaranteed to ever return
 263  * true if fence_add_callback, fence_wait or fence_enable_sw_signaling
 264  * haven't been called before.
 265  *
 266  * It's recommended for seqno fences to call fence_signal when the
 267  * operation is complete, it makes it possible to prevent issues from
 268  * wraparound between time of issue and time of use by checking the return
 269  * value of this function before calling hardware-specific wait instructions.
 270  */
 271 static inline bool
 272 fence_is_signaled(struct fence *fence)
 273 {
 274         if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 275                 return true;
 276
 277         if (fence->ops->signaled && fence->ops->signaled(fence)) {
 278                 fence_signal(fence);
 279                 return true;
 280         }
 281
 282         return false;
 283 }
 284
 285 /**
 286  * fence_is_later - return if f1 is chronologically later than f2
 287  * @f1: [in]    the first fence from the same context
 288  * @f2: [in]    the second fence from the same context
 289  *
 290  * Returns true if f1 is chronologically later than f2. Both fences must be
 291  * from the same context, since a seqno is not re-used across contexts.
 292  */
 293 static inline bool fence_is_later(struct fence *f1, struct fence *f2)
 294 {
 295         if (WARN_ON(f1->context != f2->context))
 296                 return false;
 297
 298         return (int)(f1->seqno - f2->seqno) > 0;
 299 }
 300
 301 /**
 302  * fence_later - return the chronologically later fence
 303  * @f1: [in]    the first fence from the same context
 304  * @f2: [in]    the second fence from the same context
 305  *
 306  * Returns NULL if both fences are signaled, otherwise the fence that would be
 307  * signaled last. Both fences must be from the same context, since a seqno is
 308  * not re-used across contexts.
 309  */
 310 static inline struct fence *fence_later(struct fence *f1, struct fence *f2)
 311 {
 312         if (WARN_ON(f1->context != f2->context))
 313                 return NULL;
 314
 315         /*
 316          * can't check just FENCE_FLAG_SIGNALED_BIT here, it may never have been
 317          * set if enable_signaling wasn't called, and enabling that here is
 318          * overkill.
 319          */
 320         if (fence_is_later(f1, f2))
 321                 return fence_is_signaled(f1) ? NULL : f1;
 322         else
 323                 return fence_is_signaled(f2) ? NULL : f2;
 324 }
 325
 326 signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout);
 327 signed long fence_wait_any_timeout(struct fence **fences, uint32_t count,
 328                                    bool intr, signed long timeout);
 329
 330 /**
 331  * fence_wait - sleep until the fence gets signaled
 332  * @fence:      [in]    the fence to wait on
 333  * @intr:       [in]    if true, do an interruptible wait
 334  *
 335  * This function will return -ERESTARTSYS if interrupted by a signal,
 336  * or 0 if the fence was signaled. Other error values may be
 337  * returned on custom implementations.
 338  *
 339  * Performs a synchronous wait on this fence. It is assumed the caller
 340  * directly or indirectly holds a reference to the fence, otherwise the
 341  * fence might be freed before return, resulting in undefined behavior.
 342  */
 343 static inline signed long fence_wait(struct fence *fence, bool intr)
 344 {
 345         signed long ret;
 346
 347         /* Since fence_wait_timeout cannot timeout with
 348          * MAX_SCHEDULE_TIMEOUT, only valid return values are
 349          * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
 350          */
 351         ret = fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
 352
 353         return ret < 0 ? ret : 0;
 354 }
 355
 356 u64 fence_context_alloc(unsigned num);
 357
 358 #define FENCE_TRACE(f, fmt, args...) \
 359         do {                                                            \
 360                 struct fence *__ff = (f);                               \
 361                 if (IS_ENABLED(CONFIG_FENCE_TRACE))                     \
 362                         pr_info("f %llu#%u: " fmt,                      \
 363                                 __ff->context, __ff->seqno, ##args);    \
 364         } while (0)
 365
 366 #define FENCE_WARN(f, fmt, args...) \
 367         do {                                                            \
 368                 struct fence *__ff = (f);                               \
 369                 pr_warn("f %llu#%u: " fmt, __ff->context, __ff->seqno,  \
 370                          ##args);                                       \
 371         } while (0)
 372
 373 #define FENCE_ERR(f, fmt, args...) \
 374         do {                                                            \
 375                 struct fence *__ff = (f);                               \
 376                 pr_err("f %llu#%u: " fmt, __ff->context, __ff->seqno,   \
 377                         ##args);                                        \
 378         } while (0)
 379
 380 #endif /* __LINUX_FENCE_H */