LXR linux/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/fence.h>
  24#include <linux/dma-buf.h>
  25
  26enum seqno_fence_condition {
  27        SEQNO_FENCE_WAIT_GEQUAL,
  28        SEQNO_FENCE_WAIT_NONZERO
  29};
  30
  31struct seqno_fence {
  32        struct fence base;
  33
  34        const struct fence_ops *ops;
  35        struct dma_buf *sync_buf;
  36        uint32_t seqno_ofs;
  37        enum seqno_fence_condition condition;
  38};
  39
  40extern const struct 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 */
  49static inline struct seqno_fence *
  50to_seqno_fence(struct 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 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 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 */
  94static inline void
  95seqno_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 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 fence_init for get_driver_name, so needs to be
 107         * initialized first
 108         */
 109        fence->ops = ops;
 110        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 */
 118