LXR linux/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
  18enum seqno_fence_condition {
  19        SEQNO_FENCE_WAIT_GEQUAL,
  20        SEQNO_FENCE_WAIT_NONZERO
  21};
  22
  23struct 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
  32extern 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 */
  41static inline struct seqno_fence *
  42to_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 */
  86static inline void
  87seqno_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 */
 110