1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L 2 .. c:namespace:: V4L
3 3
4 .. _VIDIOC_REQBUFS: 4 .. _VIDIOC_REQBUFS:
5 5
6 ******************** 6 ********************
7 ioctl VIDIOC_REQBUFS 7 ioctl VIDIOC_REQBUFS
8 ******************** 8 ********************
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 VIDIOC_REQBUFS - Initiate Memory Mapping, User 13 VIDIOC_REQBUFS - Initiate Memory Mapping, User Pointer I/O or DMA buffer I/O
14 14
15 Synopsis 15 Synopsis
16 ======== 16 ========
17 17
18 .. c:macro:: VIDIOC_REQBUFS 18 .. c:macro:: VIDIOC_REQBUFS
19 19
20 ``int ioctl(int fd, VIDIOC_REQBUFS, struct v4l 20 ``int ioctl(int fd, VIDIOC_REQBUFS, struct v4l2_requestbuffers *argp)``
21 21
22 Arguments 22 Arguments
23 ========= 23 =========
24 24
25 ``fd`` 25 ``fd``
26 File descriptor returned by :c:func:`open( 26 File descriptor returned by :c:func:`open()`.
27 27
28 ``argp`` 28 ``argp``
29 Pointer to struct :c:type:`v4l2_requestbuf 29 Pointer to struct :c:type:`v4l2_requestbuffers`.
30 30
31 Description 31 Description
32 =========== 32 ===========
33 33
34 This ioctl is used to initiate :ref:`memory ma 34 This ioctl is used to initiate :ref:`memory mapped <mmap>`,
35 :ref:`user pointer <userp>` or :ref:`DMABUF <d 35 :ref:`user pointer <userp>` or :ref:`DMABUF <dmabuf>` based I/O.
36 Memory mapped buffers are located in device me 36 Memory mapped buffers are located in device memory and must be allocated
37 with this ioctl before they can be mapped into 37 with this ioctl before they can be mapped into the application's address
38 space. User buffers are allocated by applicati 38 space. User buffers are allocated by applications themselves, and this
39 ioctl is merely used to switch the driver into 39 ioctl is merely used to switch the driver into user pointer I/O mode and
40 to setup some internal structures. Similarly, 40 to setup some internal structures. Similarly, DMABUF buffers are
41 allocated by applications through a device dri 41 allocated by applications through a device driver, and this ioctl only
42 configures the driver into DMABUF I/O mode wit 42 configures the driver into DMABUF I/O mode without performing any direct
43 allocation. 43 allocation.
44 44
45 To allocate device buffers applications initia 45 To allocate device buffers applications initialize all fields of the
46 struct :c:type:`v4l2_requestbuffers` structure 46 struct :c:type:`v4l2_requestbuffers` structure. They set the ``type``
47 field to the respective stream or buffer type, 47 field to the respective stream or buffer type, the ``count`` field to
48 the desired number of buffers, ``memory`` must 48 the desired number of buffers, ``memory`` must be set to the requested
49 I/O method and the ``reserved`` array must be 49 I/O method and the ``reserved`` array must be zeroed. When the ioctl is
50 called with a pointer to this structure the dr 50 called with a pointer to this structure the driver will attempt to
51 allocate the requested number of buffers and i 51 allocate the requested number of buffers and it stores the actual number
52 allocated in the ``count`` field. It can be sm 52 allocated in the ``count`` field. It can be smaller than the number
53 requested, even zero, when the driver runs out 53 requested, even zero, when the driver runs out of free memory. A larger
54 number is also possible when the driver requir 54 number is also possible when the driver requires more buffers to
55 function correctly. For example video output r 55 function correctly. For example video output requires at least two
56 buffers, one displayed and one filled by the a 56 buffers, one displayed and one filled by the application.
57 57
58 When the I/O method is not supported the ioctl 58 When the I/O method is not supported the ioctl returns an ``EINVAL`` error
59 code. 59 code.
60 60
61 Applications can call :ref:`VIDIOC_REQBUFS` ag 61 Applications can call :ref:`VIDIOC_REQBUFS` again to change the number of
62 buffers. Note that if any buffers are still ma 62 buffers. Note that if any buffers are still mapped or exported via DMABUF,
63 then :ref:`VIDIOC_REQBUFS` can only succeed if 63 then :ref:`VIDIOC_REQBUFS` can only succeed if the
64 ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` capabi 64 ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` capability is set. Otherwise
65 :ref:`VIDIOC_REQBUFS` will return the ``EBUSY` 65 :ref:`VIDIOC_REQBUFS` will return the ``EBUSY`` error code.
66 If ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` is 66 If ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` is set, then these buffers are
67 orphaned and will be freed when they are unmap 67 orphaned and will be freed when they are unmapped or when the exported DMABUF
68 fds are closed. A ``count`` value of zero free 68 fds are closed. A ``count`` value of zero frees or orphans all buffers, after
69 aborting or finishing any DMA in progress, an 69 aborting or finishing any DMA in progress, an implicit
70 :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`. 70 :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`.
71 71
72 .. c:type:: v4l2_requestbuffers 72 .. c:type:: v4l2_requestbuffers
73 73
74 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm 74 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
75 75
76 .. cssclass:: longtable 76 .. cssclass:: longtable
77 77
78 .. flat-table:: struct v4l2_requestbuffers 78 .. flat-table:: struct v4l2_requestbuffers
79 :header-rows: 0 79 :header-rows: 0
80 :stub-columns: 0 80 :stub-columns: 0
81 :widths: 1 1 2 81 :widths: 1 1 2
82 82
83 * - __u32 83 * - __u32
84 - ``count`` 84 - ``count``
85 - The number of buffers requested or gra 85 - The number of buffers requested or granted.
86 * - __u32 86 * - __u32
87 - ``type`` 87 - ``type``
88 - Type of the stream or buffers, this is 88 - Type of the stream or buffers, this is the same as the struct
89 :c:type:`v4l2_format` ``type`` field. 89 :c:type:`v4l2_format` ``type`` field. See
90 :c:type:`v4l2_buf_type` for valid valu 90 :c:type:`v4l2_buf_type` for valid values.
91 * - __u32 91 * - __u32
92 - ``memory`` 92 - ``memory``
93 - Applications set this field to ``V4L2_ 93 - Applications set this field to ``V4L2_MEMORY_MMAP``,
94 ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMOR 94 ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See
95 :c:type:`v4l2_memory`. 95 :c:type:`v4l2_memory`.
96 * - __u32 96 * - __u32
97 - ``capabilities`` 97 - ``capabilities``
98 - Set by the driver. If 0, then the driv 98 - Set by the driver. If 0, then the driver doesn't support
99 capabilities. In that case all you kno 99 capabilities. In that case all you know is that the driver is
100 guaranteed to support ``V4L2_MEMORY_MM 100 guaranteed to support ``V4L2_MEMORY_MMAP`` and *might* support
101 other :c:type:`v4l2_memory` types. It 101 other :c:type:`v4l2_memory` types. It will not support any other
102 capabilities. 102 capabilities.
103 103
104 If you want to query the capabilities 104 If you want to query the capabilities with a minimum of side-effects,
105 then this can be called with ``count`` 105 then this can be called with ``count`` set to 0, ``memory`` set to
106 ``V4L2_MEMORY_MMAP`` and ``type`` set 106 ``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will
107 free any previously allocated buffers, 107 free any previously allocated buffers, so this is typically something
108 that will be done at the start of the 108 that will be done at the start of the application.
109 * - __u8 109 * - __u8
110 - ``flags`` 110 - ``flags``
111 - Specifies additional buffer management 111 - Specifies additional buffer management attributes.
112 See :ref:`memory-flags`. 112 See :ref:`memory-flags`.
113 * - __u8 113 * - __u8
114 - ``reserved``\ [3] 114 - ``reserved``\ [3]
115 - Reserved for future extensions. 115 - Reserved for future extensions.
116 116
117 .. _v4l2-buf-capabilities: 117 .. _v4l2-buf-capabilities:
118 .. _V4L2-BUF-CAP-SUPPORTS-MMAP: 118 .. _V4L2-BUF-CAP-SUPPORTS-MMAP:
119 .. _V4L2-BUF-CAP-SUPPORTS-USERPTR: 119 .. _V4L2-BUF-CAP-SUPPORTS-USERPTR:
120 .. _V4L2-BUF-CAP-SUPPORTS-DMABUF: 120 .. _V4L2-BUF-CAP-SUPPORTS-DMABUF:
121 .. _V4L2-BUF-CAP-SUPPORTS-REQUESTS: 121 .. _V4L2-BUF-CAP-SUPPORTS-REQUESTS:
122 .. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS: 122 .. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS:
123 .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF 123 .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF:
124 .. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS: 124 .. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS:
125 .. _V4L2-BUF-CAP-SUPPORTS-MAX-NUM-BUFFERS: 125 .. _V4L2-BUF-CAP-SUPPORTS-MAX-NUM-BUFFERS:
126 .. _V4L2-BUF-CAP-SUPPORTS-REMOVE-BUFS: 126 .. _V4L2-BUF-CAP-SUPPORTS-REMOVE-BUFS:
127 127
128 .. flat-table:: V4L2 Buffer Capabilities Flags 128 .. flat-table:: V4L2 Buffer Capabilities Flags
129 :header-rows: 0 129 :header-rows: 0
130 :stub-columns: 0 130 :stub-columns: 0
131 :widths: 3 1 4 131 :widths: 3 1 4
132 132
133 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP`` 133 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP``
134 - 0x00000001 134 - 0x00000001
135 - This buffer type supports the ``V4L2_M 135 - This buffer type supports the ``V4L2_MEMORY_MMAP`` streaming mode.
136 * - ``V4L2_BUF_CAP_SUPPORTS_USERPTR`` 136 * - ``V4L2_BUF_CAP_SUPPORTS_USERPTR``
137 - 0x00000002 137 - 0x00000002
138 - This buffer type supports the ``V4L2_M 138 - This buffer type supports the ``V4L2_MEMORY_USERPTR`` streaming mode.
139 * - ``V4L2_BUF_CAP_SUPPORTS_DMABUF`` 139 * - ``V4L2_BUF_CAP_SUPPORTS_DMABUF``
140 - 0x00000004 140 - 0x00000004
141 - This buffer type supports the ``V4L2_M 141 - This buffer type supports the ``V4L2_MEMORY_DMABUF`` streaming mode.
142 * - ``V4L2_BUF_CAP_SUPPORTS_REQUESTS`` 142 * - ``V4L2_BUF_CAP_SUPPORTS_REQUESTS``
143 - 0x00000008 143 - 0x00000008
144 - This buffer type supports :ref:`reques 144 - This buffer type supports :ref:`requests <media-request-api>`.
145 * - ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS` 145 * - ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS``
146 - 0x00000010 146 - 0x00000010
147 - The kernel allows calling :ref:`VIDIOC 147 - The kernel allows calling :ref:`VIDIOC_REQBUFS` while buffers are still
148 mapped or exported via DMABUF. These o 148 mapped or exported via DMABUF. These orphaned buffers will be freed
149 when they are unmapped or when the exp 149 when they are unmapped or when the exported DMABUF fds are closed.
150 * - ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTU 150 * - ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF``
151 - 0x00000020 151 - 0x00000020
152 - Only valid for stateless decoders. If 152 - Only valid for stateless decoders. If set, then userspace can set the
153 ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` 153 ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag to hold off on returning the
154 capture buffer until the OUTPUT timest 154 capture buffer until the OUTPUT timestamp changes.
155 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HIN 155 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS``
156 - 0x00000040 156 - 0x00000040
157 - This capability is set by the driver t 157 - This capability is set by the driver to indicate that the queue supports
158 cache and memory management hints. How 158 cache and memory management hints. However, it's only valid when the
159 queue is used for :ref:`memory mapping 159 queue is used for :ref:`memory mapping <mmap>` streaming I/O. See
160 :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDAT 160 :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>`,
161 :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4 161 :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>` and
162 :ref:`V4L2_MEMORY_FLAG_NON_COHERENT <V 162 :ref:`V4L2_MEMORY_FLAG_NON_COHERENT <V4L2-MEMORY-FLAG-NON-COHERENT>`.
163 * - ``V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFER 163 * - ``V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS``
164 - 0x00000080 164 - 0x00000080
165 - If set, then the ``max_num_buffers`` f 165 - If set, then the ``max_num_buffers`` field in ``struct v4l2_create_buffers``
166 is valid. If not set, then the maximum 166 is valid. If not set, then the maximum is ``VIDEO_MAX_FRAME`` buffers.
167 * - ``V4L2_BUF_CAP_SUPPORTS_REMOVE_BUFS`` 167 * - ``V4L2_BUF_CAP_SUPPORTS_REMOVE_BUFS``
168 - 0x00000100 168 - 0x00000100
169 - If set, then ``VIDIOC_REMOVE_BUFS`` is 169 - If set, then ``VIDIOC_REMOVE_BUFS`` is supported.
170 170
171 .. _memory-flags: 171 .. _memory-flags:
172 .. _V4L2-MEMORY-FLAG-NON-COHERENT: 172 .. _V4L2-MEMORY-FLAG-NON-COHERENT:
173 173
174 .. flat-table:: Memory Consistency Flags 174 .. flat-table:: Memory Consistency Flags
175 :header-rows: 0 175 :header-rows: 0
176 :stub-columns: 0 176 :stub-columns: 0
177 :widths: 3 1 4 177 :widths: 3 1 4
178 178
179 * - ``V4L2_MEMORY_FLAG_NON_COHERENT`` 179 * - ``V4L2_MEMORY_FLAG_NON_COHERENT``
180 - 0x00000001 180 - 0x00000001
181 - A buffer is allocated either in cohere 181 - A buffer is allocated either in coherent (it will be automatically
182 coherent between the CPU and the bus) 182 coherent between the CPU and the bus) or non-coherent memory. The
183 latter can provide performance gains, 183 latter can provide performance gains, for instance the CPU cache
184 sync/flush operations can be avoided i 184 sync/flush operations can be avoided if the buffer is accessed by the
185 corresponding device only and the CPU 185 corresponding device only and the CPU does not read/write to/from that
186 buffer. However, this requires extra c 186 buffer. However, this requires extra care from the driver -- it must
187 guarantee memory consistency by issuin 187 guarantee memory consistency by issuing a cache flush/sync when
188 consistency is needed. If this flag is 188 consistency is needed. If this flag is set V4L2 will attempt to
189 allocate the buffer in non-coherent me 189 allocate the buffer in non-coherent memory. The flag takes effect
190 only if the buffer is used for :ref:`m 190 only if the buffer is used for :ref:`memory mapping <mmap>` I/O and the
191 queue reports the :ref:`V4L2_BUF_CAP_S 191 queue reports the :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS
192 <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINT 192 <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability.
193 193
194 .. raw:: latex 194 .. raw:: latex
195 195
196 \normalsize 196 \normalsize
197 197
198 Return Value 198 Return Value
199 ============ 199 ============
200 200
201 On success 0 is returned, on error -1 and the 201 On success 0 is returned, on error -1 and the ``errno`` variable is set
202 appropriately. The generic error codes are des 202 appropriately. The generic error codes are described at the
203 :ref:`Generic Error Codes <gen-errors>` chapte 203 :ref:`Generic Error Codes <gen-errors>` chapter.
204 204
205 EINVAL 205 EINVAL
206 The buffer type (``type`` field) or the re 206 The buffer type (``type`` field) or the requested I/O method
207 (``memory``) is not supported. 207 (``memory``) is not supported.
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