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
26enum seqno_fence_condition {
27 SEQNO_FENCE_WAIT_GEQUAL,
28 SEQNO_FENCE_WAIT_NONZERO
29};
30
31struct 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
40extern 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 */
49static inline struct seqno_fence *
50to_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 */
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 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 */
118