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 
26 enum seqno_fence_condition {
27 	SEQNO_FENCE_WAIT_GEQUAL,
28 	SEQNO_FENCE_WAIT_NONZERO
29 };
30 
31 struct 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 
40 extern 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  */
49 static inline struct seqno_fence *
to_seqno_fence(struct dma_fence * fence)50 to_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  */
94 static inline void
seqno_fence_init(struct seqno_fence * fence,spinlock_t * lock,struct dma_buf * sync_buf,uint32_t context,uint32_t seqno_ofs,uint32_t seqno,enum seqno_fence_condition cond,const struct dma_fence_ops * ops)95 seqno_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