xref: /openbmc/linux/include/uapi/linux/dma-buf.h (revision 59474049)
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  */
54 struct 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  */
118 struct 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  */
150 struct 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