1/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
2/*
3 * Framework for buffer objects that can be shared across devices/subsystems.
4 *
5 * Copyright(C) 2015 Intel Ltd
6 *
7 * This program is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License version 2 as published by
9 * the Free Software Foundation.
10 *
11 * This program is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
14 * more details.
15 *
16 * You should have received a copy of the GNU General Public License along with
17 * this program. If not, see <http://www.gnu.org/licenses/>.
18 */
19
20#ifndef _DMA_BUF_UAPI_H_
21#define _DMA_BUF_UAPI_H_
22
23#include <linux/types.h>
24
25/**
26 * struct dma_buf_sync - Synchronize with CPU access.
27 *
28 * When a DMA buffer is accessed from the CPU via mmap, it is not always
29 * possible to guarantee coherency between the CPU-visible map and underlying
30 * memory. To manage coherency, DMA_BUF_IOCTL_SYNC must be used to bracket
31 * any CPU access to give the kernel the chance to shuffle memory around if
32 * needed.
33 *
34 * Prior to accessing the map, the client must call DMA_BUF_IOCTL_SYNC
35 * with DMA_BUF_SYNC_START and the appropriate read/write flags. Once the
36 * access is complete, the client should call DMA_BUF_IOCTL_SYNC with
37 * DMA_BUF_SYNC_END and the same read/write flags.
38 *
39 * The synchronization provided via DMA_BUF_IOCTL_SYNC only provides cache
40 * coherency. It does not prevent other processes or devices from
41 * accessing the memory at the same time. If synchronization with a GPU or
42 * other device driver is required, it is the client's responsibility to
43 * wait for buffer to be ready for reading or writing before calling this
44 * ioctl with DMA_BUF_SYNC_START. Likewise, the client must ensure that
45 * follow-up work is not submitted to GPU or other device driver until
46 * after this ioctl has been called with DMA_BUF_SYNC_END?
47 *
48 * If the driver or API with which the client is interacting uses implicit
49 * synchronization, waiting for prior work to complete can be done via
50 * poll() on the DMA buffer file descriptor. If the driver or API requires
51 * explicit synchronization, the client may have to wait on a sync_file or
52 * other synchronization primitive outside the scope of the DMA buffer API.
53 */
54struct dma_buf_sync {
55 /**
56 * @flags: Set of access flags
57 *
58 * DMA_BUF_SYNC_START:
59 * Indicates the start of a map access session.
60 *
61 * DMA_BUF_SYNC_END:
62 * Indicates the end of a map access session.
63 *
64 * DMA_BUF_SYNC_READ:
65 * Indicates that the mapped DMA buffer will be read by the
66 * client via the CPU map.
67 *
68 * DMA_BUF_SYNC_WRITE:
69 * Indicates that the mapped DMA buffer will be written by the
70 * client via the CPU map.
71 *
72 * DMA_BUF_SYNC_RW:
73 * An alias for DMA_BUF_SYNC_READ | DMA_BUF_SYNC_WRITE.
74 */
75 __u64 flags;
76};
77
78#define DMA_BUF_SYNC_READ (1 << 0)
79#define DMA_BUF_SYNC_WRITE (2 << 0)
80#define DMA_BUF_SYNC_RW (DMA_BUF_SYNC_READ | DMA_BUF_SYNC_WRITE)
81#define DMA_BUF_SYNC_START (0 << 2)
82#define DMA_BUF_SYNC_END (1 << 2)
83#define DMA_BUF_SYNC_VALID_FLAGS_MASK \
84 (DMA_BUF_SYNC_RW | DMA_BUF_SYNC_END)
85
86#define DMA_BUF_NAME_LEN 32
87
88/**
89 * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf
90 *
91 * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve the
92 * current set of fences on a dma-buf file descriptor as a sync_file. CPU
93 * waits via poll() or other driver-specific mechanisms typically wait on
94 * whatever fences are on the dma-buf at the time the wait begins. This
95 * is similar except that it takes a snapshot of the current fences on the
96 * dma-buf for waiting later instead of waiting immediately. This is
97 * useful for modern graphics APIs such as Vulkan which assume an explicit
98 * synchronization model but still need to inter-operate with dma-buf.
99 *
100 * The intended usage pattern is the following:
101 *
102 * 1. Export a sync_file with flags corresponding to the expected GPU usage
103 * via DMA_BUF_IOCTL_EXPORT_SYNC_FILE.
104 *
105 * 2. Submit rendering work which uses the dma-buf. The work should wait on
106 * the exported sync file before rendering and produce another sync_file
107 * when complete.
108 *
109 * 3. Import the rendering-complete sync_file into the dma-buf with flags
110 * corresponding to the GPU usage via DMA_BUF_IOCTL_IMPORT_SYNC_FILE.
111 *
112 * Unlike doing implicit synchronization via a GPU kernel driver's exec ioctl,
113 * the above is not a single atomic operation. If userspace wants to ensure
114 * ordering via these fences, it is the respnosibility of userspace to use
115 * locks or other mechanisms to ensure that no other context adds fences or
116 * submits work between steps 1 and 3 above.
117 */
118struct dma_buf_export_sync_file {
119 /**
120 * @flags: Read/write flags
121 *
122 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
123 *
124 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
125 * the returned sync file waits on any writers of the dma-buf to
126 * complete. Waiting on the returned sync file is equivalent to
127 * poll() with POLLIN.
128 *
129 * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on
130 * any users of the dma-buf (read or write) to complete. Waiting
131 * on the returned sync file is equivalent to poll() with POLLOUT.
132 * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this
133 * is equivalent to just DMA_BUF_SYNC_WRITE.
134 */
135 __u32 flags;
136 /** @fd: Returned sync file descriptor */
137 __s32 fd;
138};
139
140/**
141 * struct dma_buf_import_sync_file - Insert a sync_file into a dma-buf
142 *
143 * Userspace can perform a DMA_BUF_IOCTL_IMPORT_SYNC_FILE to insert a
144 * sync_file into a dma-buf for the purposes of implicit synchronization
145 * with other dma-buf consumers. This allows clients using explicitly
146 * synchronized APIs such as Vulkan to inter-op with dma-buf consumers
147 * which expect implicit synchronization such as OpenGL or most media
148 * drivers/video.
149 */
150struct dma_buf_import_sync_file {
151 /**
152 * @flags: Read/write flags
153 *
154 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
155 *
156 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
157 * this inserts the sync_file as a read-only fence. Any subsequent
158 * implicitly synchronized writes to this dma-buf will wait on this
159 * fence but reads will not.
160 *
161 * If DMA_BUF_SYNC_WRITE is set, this inserts the sync_file as a
162 * write fence. All subsequent implicitly synchronized access to
163 * this dma-buf will wait on this fence.
164 */
165 __u32 flags;
166 /** @fd: Sync file descriptor */
167 __s32 fd;
168};
169
170#define DMA_BUF_BASE 'b'
171#define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
172
173/* 32/64bitness of this uapi was botched in android, there's no difference
174 * between them in actual uapi, they're just different numbers.
175 */
176#define DMA_BUF_SET_NAME _IOW(DMA_BUF_BASE, 1, const char *)
177#define DMA_BUF_SET_NAME_A _IOW(DMA_BUF_BASE, 1, __u32)
178#define DMA_BUF_SET_NAME_B _IOW(DMA_BUF_BASE, 1, __u64)
179#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
180#define DMA_BUF_IOCTL_IMPORT_SYNC_FILE _IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file)
181
182#endif
183

source code of linux/include/uapi/linux/dma-buf.h

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