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  *
  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  */
  72 struct 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
  85 enum 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
  91 typedef 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  */
 101 struct 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
 166 struct 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
 179 void fence_init(struct fence *fence, const struct fence_ops *ops,
 180                 spinlock_t *lock, u64 context, unsigned seqno);
 181
 182 void fence_release(struct kref *kref);
 183 void 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  */
 191 static 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  */
 204 static 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  */
 216 static inline void fence_put(struct fence *fence)
 217 {
 218         if (fence)
 219                 kref_put(&fence->refcount, fence_release);
 220 }
 221
 222 int fence_signal(struct fence *fence);
 223 int fence_signal_locked(struct fence *fence);
 224 signed long fence_default_wait(struct fence *fence, bool intr, signed long timeout);
 225 int fence_add_callback(struct fence *fence, struct fence_cb *cb,
 226                        fence_func_t func);
 227 bool fence_remove_callback(struct fence *fence, struct fence_cb *cb);
 228 void 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  */
 241 static inline bool
 242 fence_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  */
 269 static inline bool
 270 fence_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  */
 291 static 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  */
 308 static 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
 324 signed long fence_wait_timeout(struct fence *, bool intr, signed long timeout);
 325 signed 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  */
 341 static 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
 354 u64 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 */