dma-buf.h

  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/ioctl.h>
 24#include <linux/types.h>
 25
 26/**
 27 * struct dma_buf_sync - Synchronize with CPU access.
 28 *
 29 * When a DMA buffer is accessed from the CPU via mmap, it is not always
 30 * possible to guarantee coherency between the CPU-visible map and underlying
 31 * memory.  To manage coherency, DMA_BUF_IOCTL_SYNC must be used to bracket
 32 * any CPU access to give the kernel the chance to shuffle memory around if
 33 * needed.
 34 *
 35 * Prior to accessing the map, the client must call DMA_BUF_IOCTL_SYNC
 36 * with DMA_BUF_SYNC_START and the appropriate read/write flags.  Once the
 37 * access is complete, the client should call DMA_BUF_IOCTL_SYNC with
 38 * DMA_BUF_SYNC_END and the same read/write flags.
 39 *
 40 * The synchronization provided via DMA_BUF_IOCTL_SYNC only provides cache
 41 * coherency.  It does not prevent other processes or devices from
 42 * accessing the memory at the same time.  If synchronization with a GPU or
 43 * other device driver is required, it is the client's responsibility to
 44 * wait for buffer to be ready for reading or writing before calling this
 45 * ioctl with DMA_BUF_SYNC_START.  Likewise, the client must ensure that
 46 * follow-up work is not submitted to GPU or other device driver until
 47 * after this ioctl has been called with DMA_BUF_SYNC_END?
 48 *
 49 * If the driver or API with which the client is interacting uses implicit
 50 * synchronization, waiting for prior work to complete can be done via
 51 * poll() on the DMA buffer file descriptor.  If the driver or API requires
 52 * explicit synchronization, the client may have to wait on a sync_file or
 53 * other synchronization primitive outside the scope of the DMA buffer API.
 54 */
 55struct dma_buf_sync {
 56	/**
 57	 * @flags: Set of access flags
 58	 *
 59	 * DMA_BUF_SYNC_START:
 60	 *     Indicates the start of a map access session.
 61	 *
 62	 * DMA_BUF_SYNC_END:
 63	 *     Indicates the end of a map access session.
 64	 *
 65	 * DMA_BUF_SYNC_READ:
 66	 *     Indicates that the mapped DMA buffer will be read by the
 67	 *     client via the CPU map.
 68	 *
 69	 * DMA_BUF_SYNC_WRITE:
 70	 *     Indicates that the mapped DMA buffer will be written by the
 71	 *     client via the CPU map.
 72	 *
 73	 * DMA_BUF_SYNC_RW:
 74	 *     An alias for DMA_BUF_SYNC_READ | DMA_BUF_SYNC_WRITE.
 75	 */
 76	__u64 flags;
 77};
 78
 79#define DMA_BUF_SYNC_READ      (1 << 0)
 80#define DMA_BUF_SYNC_WRITE     (2 << 0)
 81#define DMA_BUF_SYNC_RW        (DMA_BUF_SYNC_READ | DMA_BUF_SYNC_WRITE)
 82#define DMA_BUF_SYNC_START     (0 << 2)
 83#define DMA_BUF_SYNC_END       (1 << 2)
 84#define DMA_BUF_SYNC_VALID_FLAGS_MASK \
 85	(DMA_BUF_SYNC_RW | DMA_BUF_SYNC_END)
 86
 87#define DMA_BUF_NAME_LEN	32
 88
 89/**
 90 * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf
 91 *
 92 * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve the
 93 * current set of fences on a dma-buf file descriptor as a sync_file.  CPU
 94 * waits via poll() or other driver-specific mechanisms typically wait on
 95 * whatever fences are on the dma-buf at the time the wait begins.  This
 96 * is similar except that it takes a snapshot of the current fences on the
 97 * dma-buf for waiting later instead of waiting immediately.  This is
 98 * useful for modern graphics APIs such as Vulkan which assume an explicit
 99 * synchronization model but still need to inter-operate with dma-buf.
100 *
101 * The intended usage pattern is the following:
102 *
103 *  1. Export a sync_file with flags corresponding to the expected GPU usage
104 *     via DMA_BUF_IOCTL_EXPORT_SYNC_FILE.
105 *
106 *  2. Submit rendering work which uses the dma-buf.  The work should wait on
107 *     the exported sync file before rendering and produce another sync_file
108 *     when complete.
109 *
110 *  3. Import the rendering-complete sync_file into the dma-buf with flags
111 *     corresponding to the GPU usage via DMA_BUF_IOCTL_IMPORT_SYNC_FILE.
112 *
113 * Unlike doing implicit synchronization via a GPU kernel driver's exec ioctl,
114 * the above is not a single atomic operation.  If userspace wants to ensure
115 * ordering via these fences, it is the respnosibility of userspace to use
116 * locks or other mechanisms to ensure that no other context adds fences or
117 * submits work between steps 1 and 3 above.
118 */
119struct dma_buf_export_sync_file {
120	/**
121	 * @flags: Read/write flags
122	 *
123	 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
124	 *
125	 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
126	 * the returned sync file waits on any writers of the dma-buf to
127	 * complete.  Waiting on the returned sync file is equivalent to
128	 * poll() with POLLIN.
129	 *
130	 * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on
131	 * any users of the dma-buf (read or write) to complete.  Waiting
132	 * on the returned sync file is equivalent to poll() with POLLOUT.
133	 * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this
134	 * is equivalent to just DMA_BUF_SYNC_WRITE.
135	 */
136	__u32 flags;
137	/** @fd: Returned sync file descriptor */
138	__s32 fd;
139};
140
141/**
142 * struct dma_buf_import_sync_file - Insert a sync_file into a dma-buf
143 *
144 * Userspace can perform a DMA_BUF_IOCTL_IMPORT_SYNC_FILE to insert a
145 * sync_file into a dma-buf for the purposes of implicit synchronization
146 * with other dma-buf consumers.  This allows clients using explicitly
147 * synchronized APIs such as Vulkan to inter-op with dma-buf consumers
148 * which expect implicit synchronization such as OpenGL or most media
149 * drivers/video.
150 */
151struct dma_buf_import_sync_file {
152	/**
153	 * @flags: Read/write flags
154	 *
155	 * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both.
156	 *
157	 * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set,
158	 * this inserts the sync_file as a read-only fence.  Any subsequent
159	 * implicitly synchronized writes to this dma-buf will wait on this
160	 * fence but reads will not.
161	 *
162	 * If DMA_BUF_SYNC_WRITE is set, this inserts the sync_file as a
163	 * write fence.  All subsequent implicitly synchronized access to
164	 * this dma-buf will wait on this fence.
165	 */
166	__u32 flags;
167	/** @fd: Sync file descriptor */
168	__s32 fd;
169};
170
171#define DMA_BUF_BASE		'b'
172#define DMA_BUF_IOCTL_SYNC	_IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
173
174/* 32/64bitness of this uapi was botched in android, there's no difference
175 * between them in actual uapi, they're just different numbers.
176 */
177#define DMA_BUF_SET_NAME	_IOW(DMA_BUF_BASE, 1, const char *)
178#define DMA_BUF_SET_NAME_A	_IOW(DMA_BUF_BASE, 1, __u32)
179#define DMA_BUF_SET_NAME_B	_IOW(DMA_BUF_BASE, 1, __u64)
180#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE	_IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
181#define DMA_BUF_IOCTL_IMPORT_SYNC_FILE	_IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file)
182
183#endif