include/linux/seqno-fence.h

   1 /*
   2  * seqno-fence, using a dma-buf to synchronize fencing
   3  *
   4  * Copyright (C) 2012 Texas Instruments
   5  * Copyright (C) 2012 Canonical Ltd
   6  * Authors:
   7  *   Rob Clark <robdclark@gmail.com>
   8  *   Maarten Lankhorst <maarten.lankhorst@canonical.com>
   9  *
  10  * This program is free software; you can redistribute it and/or modify it
  11  * under the terms of the GNU General Public License version 2 as published by
  12  * the Free Software Foundation.
  13  *
  14  * This program is distributed in the hope that it will be useful, but WITHOUT
  15  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  16  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  17  * more details.
  18  */
  19
  20 #ifndef __LINUX_SEQNO_FENCE_H
  21 #define __LINUX_SEQNO_FENCE_H
  22
  23 #include <linux/dma-fence.h>
  24 #include <linux/dma-buf.h>
  25
  26 enum seqno_fence_condition {
  27         SEQNO_FENCE_WAIT_GEQUAL,
  28         SEQNO_FENCE_WAIT_NONZERO
  29 };
  30
  31 struct seqno_fence {
  32         struct dma_fence base;
  33
  34         const struct dma_fence_ops *ops;
  35         struct dma_buf *sync_buf;
  36         uint32_t seqno_ofs;
  37         enum seqno_fence_condition condition;
  38 };
  39
  40 extern const struct dma_fence_ops seqno_fence_ops;
  41
  42 /**
  43  * to_seqno_fence - cast a fence to a seqno_fence
  44  * @fence: fence to cast to a seqno_fence
  45  *
  46  * Returns NULL if the fence is not a seqno_fence,
  47  * or the seqno_fence otherwise.
  48  */
  49 static inline struct seqno_fence *
  50 to_seqno_fence(struct dma_fence *fence)
  51 {
  52         if (fence->ops != &seqno_fence_ops)
  53                 return NULL;
  54         return container_of(fence, struct seqno_fence, base);
  55 }
  56
  57 /**
  58  * seqno_fence_init - initialize a seqno fence
  59  * @fence: seqno_fence to initialize
  60  * @lock: pointer to spinlock to use for fence
  61  * @sync_buf: buffer containing the memory location to signal on
  62  * @context: the execution context this fence is a part of
  63  * @seqno_ofs: the offset within @sync_buf
  64  * @seqno: the sequence # to signal on
  65  * @cond: fence wait condition
  66  * @ops: the fence_ops for operations on this seqno fence
  67  *
  68  * This function initializes a struct seqno_fence with passed parameters,
  69  * and takes a reference on sync_buf which is released on fence destruction.
  70  *
  71  * A seqno_fence is a dma_fence which can complete in software when
  72  * enable_signaling is called, but it also completes when
  73  * (s32)((sync_buf)[seqno_ofs] - seqno) >= 0 is true
  74  *
  75  * The seqno_fence will take a refcount on the sync_buf until it's
  76  * destroyed, but actual lifetime of sync_buf may be longer if one of the
  77  * callers take a reference to it.
  78  *
  79  * Certain hardware have instructions to insert this type of wait condition
  80  * in the command stream, so no intervention from software would be needed.
  81  * This type of fence can be destroyed before completed, however a reference
  82  * on the sync_buf dma-buf can be taken. It is encouraged to re-use the same
  83  * dma-buf for sync_buf, since mapping or unmapping the sync_buf to the
  84  * device's vm can be expensive.
  85  *
  86  * It is recommended for creators of seqno_fence to call dma_fence_signal()
  87  * before destruction. This will prevent possible issues from wraparound at
  88  * time of issue vs time of check, since users can check dma_fence_is_signaled()
  89  * before submitting instructions for the hardware to wait on the fence.
  90  * However, when ops.enable_signaling is not called, it doesn't have to be
  91  * done as soon as possible, just before there's any real danger of seqno
  92  * wraparound.
  93  */
  94 static inline void
  95 seqno_fence_init(struct seqno_fence *fence, spinlock_t *lock,
  96                  struct dma_buf *sync_buf,  uint32_t context,
  97                  uint32_t seqno_ofs, uint32_t seqno,
  98                  enum seqno_fence_condition cond,
  99                  const struct dma_fence_ops *ops)
 100 {
 101         BUG_ON(!fence || !sync_buf || !ops);
 102         BUG_ON(!ops->wait || !ops->enable_signaling ||
 103                !ops->get_driver_name || !ops->get_timeline_name);
 104
 105         /*
 106          * ops is used in dma_fence_init for get_driver_name, so needs to be
 107          * initialized first
 108          */
 109         fence->ops = ops;
 110         dma_fence_init(&fence->base, &seqno_fence_ops, lock, context, seqno);
 111         get_dma_buf(sync_buf);
 112         fence->sync_buf = sync_buf;
 113         fence->seqno_ofs = seqno_ofs;
 114         fence->condition = cond;
 115 }
 116
 117 #endif /* __LINUX_SEQNO_FENCE_H */