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 *
to_seqno_fence(struct dma_fence * 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
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)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 */
110