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 */