include/linux/seqno-fence.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * seqno-fence, using a dma-buf to synchronize fencing
   4  *
   5  * Copyright (C) 2012 Texas Instruments
   6  * Copyright (C) 2012 Canonical Ltd
   7  * Authors:
   8  *   Rob Clark <robdclark@gmail.com>
   9  *   Maarten Lankhorst <maarten.lankhorst@canonical.com>
  10  */
  11
  12 #ifndef __LINUX_SEQNO_FENCE_H
  13 #define __LINUX_SEQNO_FENCE_H
  14
  15 #include <linux/dma-fence.h>
  16 #include <linux/dma-buf.h>
  17
  18 enum seqno_fence_condition {
  19         SEQNO_FENCE_WAIT_GEQUAL,
  20         SEQNO_FENCE_WAIT_NONZERO
  21 };
  22
  23 struct seqno_fence {
  24         struct dma_fence base;
  25
  26         const struct dma_fence_ops *ops;
  27         struct dma_buf *sync_buf;
  28         uint32_t seqno_ofs;
  29         enum seqno_fence_condition condition;
  30 };
  31
  32 extern const struct dma_fence_ops seqno_fence_ops;
  33
  34 /**
  35  * to_seqno_fence - cast a fence to a seqno_fence
  36  * @fence: fence to cast to a seqno_fence
  37  *
  38  * Returns NULL if the fence is not a seqno_fence,
  39  * or the seqno_fence otherwise.
  40  */
  41 static inline struct seqno_fence *
  42 to_seqno_fence(struct dma_fence *fence)
  43 {
  44         if (fence->ops != &seqno_fence_ops)
  45                 return NULL;
  46         return container_of(fence, struct seqno_fence, base);
  47 }
  48
  49 /**
  50  * seqno_fence_init - initialize a seqno fence
  51  * @fence: seqno_fence to initialize
  52  * @lock: pointer to spinlock to use for fence
  53  * @sync_buf: buffer containing the memory location to signal on
  54  * @context: the execution context this fence is a part of
  55  * @seqno_ofs: the offset within @sync_buf
  56  * @seqno: the sequence # to signal on
  57  * @cond: fence wait condition
  58  * @ops: the fence_ops for operations on this seqno fence
  59  *
  60  * This function initializes a struct seqno_fence with passed parameters,
  61  * and takes a reference on sync_buf which is released on fence destruction.
  62  *
  63  * A seqno_fence is a dma_fence which can complete in software when
  64  * enable_signaling is called, but it also completes when
  65  * (s32)((sync_buf)[seqno_ofs] - seqno) >= 0 is true
  66  *
  67  * The seqno_fence will take a refcount on the sync_buf until it's
  68  * destroyed, but actual lifetime of sync_buf may be longer if one of the
  69  * callers take a reference to it.
  70  *
  71  * Certain hardware have instructions to insert this type of wait condition
  72  * in the command stream, so no intervention from software would be needed.
  73  * This type of fence can be destroyed before completed, however a reference
  74  * on the sync_buf dma-buf can be taken. It is encouraged to re-use the same
  75  * dma-buf for sync_buf, since mapping or unmapping the sync_buf to the
  76  * device's vm can be expensive.
  77  *
  78  * It is recommended for creators of seqno_fence to call dma_fence_signal()
  79  * before destruction. This will prevent possible issues from wraparound at
  80  * time of issue vs time of check, since users can check dma_fence_is_signaled()
  81  * before submitting instructions for the hardware to wait on the fence.
  82  * However, when ops.enable_signaling is not called, it doesn't have to be
  83  * done as soon as possible, just before there's any real danger of seqno
  84  * wraparound.
  85  */
  86 static inline void
  87 seqno_fence_init(struct seqno_fence *fence, spinlock_t *lock,
  88                  struct dma_buf *sync_buf,  uint32_t context,
  89                  uint32_t seqno_ofs, uint32_t seqno,
  90                  enum seqno_fence_condition cond,
  91                  const struct dma_fence_ops *ops)
  92 {
  93         BUG_ON(!fence || !sync_buf || !ops);
  94         BUG_ON(!ops->wait || !ops->enable_signaling ||
  95                !ops->get_driver_name || !ops->get_timeline_name);
  96
  97         /*
  98          * ops is used in dma_fence_init for get_driver_name, so needs to be
  99          * initialized first
 100          */
 101         fence->ops = ops;
 102         dma_fence_init(&fence->base, &seqno_fence_ops, lock, context, seqno);
 103         get_dma_buf(sync_buf);
 104         fence->sync_buf = sync_buf;
 105         fence->seqno_ofs = seqno_ofs;
 106         fence->condition = cond;
 107 }
 108
 109 #endif /* __LINUX_SEQNO_FENCE_H */