1 .. SPDX-License-Identifier: GFDL-1.1-no-invari !! 1 .. Permission is granted to copy, distribute and/or modify this
2 .. c:namespace:: V4L !! 2 .. document under the terms of the GNU Free Documentation License,
>> 3 .. Version 1.1 or any later version published by the Free Software
>> 4 .. Foundation, with no Invariant Sections, no Front-Cover Texts
>> 5 .. and no Back-Cover Texts. A copy of the license is included at
>> 6 .. Documentation/userspace-api/media/fdl-appendix.rst.
>> 7 ..
>> 8 .. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
3 9
4 .. _VIDIOC_REQBUFS: 10 .. _VIDIOC_REQBUFS:
5 11
6 ******************** 12 ********************
7 ioctl VIDIOC_REQBUFS 13 ioctl VIDIOC_REQBUFS
8 ******************** 14 ********************
9 15
10 Name 16 Name
11 ==== 17 ====
12 18
13 VIDIOC_REQBUFS - Initiate Memory Mapping, User 19 VIDIOC_REQBUFS - Initiate Memory Mapping, User Pointer I/O or DMA buffer I/O
14 20
>> 21
15 Synopsis 22 Synopsis
16 ======== 23 ========
17 24
18 .. c:macro:: VIDIOC_REQBUFS !! 25 .. c:function:: int ioctl( int fd, VIDIOC_REQBUFS, struct v4l2_requestbuffers *argp )
>> 26 :name: VIDIOC_REQBUFS
19 27
20 ``int ioctl(int fd, VIDIOC_REQBUFS, struct v4l <<
21 28
22 Arguments 29 Arguments
23 ========= 30 =========
24 31
25 ``fd`` 32 ``fd``
26 File descriptor returned by :c:func:`open( !! 33 File descriptor returned by :ref:`open() <func-open>`.
27 34
28 ``argp`` 35 ``argp``
29 Pointer to struct :c:type:`v4l2_requestbuf 36 Pointer to struct :c:type:`v4l2_requestbuffers`.
30 37
31 Description 38 Description
32 =========== 39 ===========
33 40
34 This ioctl is used to initiate :ref:`memory ma 41 This ioctl is used to initiate :ref:`memory mapped <mmap>`,
35 :ref:`user pointer <userp>` or :ref:`DMABUF <d 42 :ref:`user pointer <userp>` or :ref:`DMABUF <dmabuf>` based I/O.
36 Memory mapped buffers are located in device me 43 Memory mapped buffers are located in device memory and must be allocated
37 with this ioctl before they can be mapped into 44 with this ioctl before they can be mapped into the application's address
38 space. User buffers are allocated by applicati 45 space. User buffers are allocated by applications themselves, and this
39 ioctl is merely used to switch the driver into 46 ioctl is merely used to switch the driver into user pointer I/O mode and
40 to setup some internal structures. Similarly, 47 to setup some internal structures. Similarly, DMABUF buffers are
41 allocated by applications through a device dri 48 allocated by applications through a device driver, and this ioctl only
42 configures the driver into DMABUF I/O mode wit 49 configures the driver into DMABUF I/O mode without performing any direct
43 allocation. 50 allocation.
44 51
45 To allocate device buffers applications initia 52 To allocate device buffers applications initialize all fields of the
46 struct :c:type:`v4l2_requestbuffers` structure 53 struct :c:type:`v4l2_requestbuffers` structure. They set the ``type``
47 field to the respective stream or buffer type, 54 field to the respective stream or buffer type, the ``count`` field to
48 the desired number of buffers, ``memory`` must 55 the desired number of buffers, ``memory`` must be set to the requested
49 I/O method and the ``reserved`` array must be 56 I/O method and the ``reserved`` array must be zeroed. When the ioctl is
50 called with a pointer to this structure the dr 57 called with a pointer to this structure the driver will attempt to
51 allocate the requested number of buffers and i 58 allocate the requested number of buffers and it stores the actual number
52 allocated in the ``count`` field. It can be sm 59 allocated in the ``count`` field. It can be smaller than the number
53 requested, even zero, when the driver runs out 60 requested, even zero, when the driver runs out of free memory. A larger
54 number is also possible when the driver requir 61 number is also possible when the driver requires more buffers to
55 function correctly. For example video output r 62 function correctly. For example video output requires at least two
56 buffers, one displayed and one filled by the a 63 buffers, one displayed and one filled by the application.
57 64
58 When the I/O method is not supported the ioctl 65 When the I/O method is not supported the ioctl returns an ``EINVAL`` error
59 code. 66 code.
60 67
61 Applications can call :ref:`VIDIOC_REQBUFS` ag 68 Applications can call :ref:`VIDIOC_REQBUFS` again to change the number of
62 buffers. Note that if any buffers are still ma 69 buffers. Note that if any buffers are still mapped or exported via DMABUF,
63 then :ref:`VIDIOC_REQBUFS` can only succeed if 70 then :ref:`VIDIOC_REQBUFS` can only succeed if the
64 ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` capabi 71 ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` capability is set. Otherwise
65 :ref:`VIDIOC_REQBUFS` will return the ``EBUSY` 72 :ref:`VIDIOC_REQBUFS` will return the ``EBUSY`` error code.
66 If ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` is 73 If ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` is set, then these buffers are
67 orphaned and will be freed when they are unmap 74 orphaned and will be freed when they are unmapped or when the exported DMABUF
68 fds are closed. A ``count`` value of zero free 75 fds are closed. A ``count`` value of zero frees or orphans all buffers, after
69 aborting or finishing any DMA in progress, an 76 aborting or finishing any DMA in progress, an implicit
70 :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`. 77 :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`.
71 78
>> 79
72 .. c:type:: v4l2_requestbuffers 80 .. c:type:: v4l2_requestbuffers
73 81
74 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm !! 82 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
75 <<
76 .. cssclass:: longtable <<
77 83
78 .. flat-table:: struct v4l2_requestbuffers 84 .. flat-table:: struct v4l2_requestbuffers
79 :header-rows: 0 85 :header-rows: 0
80 :stub-columns: 0 86 :stub-columns: 0
81 :widths: 1 1 2 87 :widths: 1 1 2
82 88
83 * - __u32 89 * - __u32
84 - ``count`` 90 - ``count``
85 - The number of buffers requested or gra 91 - The number of buffers requested or granted.
86 * - __u32 92 * - __u32
87 - ``type`` 93 - ``type``
88 - Type of the stream or buffers, this is 94 - Type of the stream or buffers, this is the same as the struct
89 :c:type:`v4l2_format` ``type`` field. 95 :c:type:`v4l2_format` ``type`` field. See
90 :c:type:`v4l2_buf_type` for valid valu 96 :c:type:`v4l2_buf_type` for valid values.
91 * - __u32 97 * - __u32
92 - ``memory`` 98 - ``memory``
93 - Applications set this field to ``V4L2_ 99 - Applications set this field to ``V4L2_MEMORY_MMAP``,
94 ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMOR 100 ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See
95 :c:type:`v4l2_memory`. 101 :c:type:`v4l2_memory`.
96 * - __u32 102 * - __u32
97 - ``capabilities`` 103 - ``capabilities``
98 - Set by the driver. If 0, then the driv 104 - Set by the driver. If 0, then the driver doesn't support
99 capabilities. In that case all you kno 105 capabilities. In that case all you know is that the driver is
100 guaranteed to support ``V4L2_MEMORY_MM 106 guaranteed to support ``V4L2_MEMORY_MMAP`` and *might* support
101 other :c:type:`v4l2_memory` types. It 107 other :c:type:`v4l2_memory` types. It will not support any other
102 capabilities. 108 capabilities.
103 109
104 If you want to query the capabilities 110 If you want to query the capabilities with a minimum of side-effects,
105 then this can be called with ``count`` 111 then this can be called with ``count`` set to 0, ``memory`` set to
106 ``V4L2_MEMORY_MMAP`` and ``type`` set 112 ``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will
107 free any previously allocated buffers, 113 free any previously allocated buffers, so this is typically something
108 that will be done at the start of the 114 that will be done at the start of the application.
109 * - __u8 !! 115 * - __u32
110 - ``flags`` !! 116 - ``reserved``\ [1]
111 - Specifies additional buffer management !! 117 - A place holder for future extensions. Drivers and applications
112 See :ref:`memory-flags`. !! 118 must set the array to zero.
113 * - __u8 !! 119
114 - ``reserved``\ [3] !! 120 .. tabularcolumns:: |p{6.1cm}|p{2.2cm}|p{8.7cm}|
115 - Reserved for future extensions. <<
116 121
117 .. _v4l2-buf-capabilities: 122 .. _v4l2-buf-capabilities:
118 .. _V4L2-BUF-CAP-SUPPORTS-MMAP: 123 .. _V4L2-BUF-CAP-SUPPORTS-MMAP:
119 .. _V4L2-BUF-CAP-SUPPORTS-USERPTR: 124 .. _V4L2-BUF-CAP-SUPPORTS-USERPTR:
120 .. _V4L2-BUF-CAP-SUPPORTS-DMABUF: 125 .. _V4L2-BUF-CAP-SUPPORTS-DMABUF:
121 .. _V4L2-BUF-CAP-SUPPORTS-REQUESTS: 126 .. _V4L2-BUF-CAP-SUPPORTS-REQUESTS:
122 .. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS: 127 .. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS:
123 .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF 128 .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF:
124 .. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS: !! 129
125 .. _V4L2-BUF-CAP-SUPPORTS-MAX-NUM-BUFFERS: !! 130 .. cssclass:: longtable
126 .. _V4L2-BUF-CAP-SUPPORTS-REMOVE-BUFS: <<
127 131
128 .. flat-table:: V4L2 Buffer Capabilities Flags 132 .. flat-table:: V4L2 Buffer Capabilities Flags
129 :header-rows: 0 133 :header-rows: 0
130 :stub-columns: 0 134 :stub-columns: 0
131 :widths: 3 1 4 135 :widths: 3 1 4
132 136
133 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP`` 137 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP``
134 - 0x00000001 138 - 0x00000001
135 - This buffer type supports the ``V4L2_M 139 - This buffer type supports the ``V4L2_MEMORY_MMAP`` streaming mode.
136 * - ``V4L2_BUF_CAP_SUPPORTS_USERPTR`` 140 * - ``V4L2_BUF_CAP_SUPPORTS_USERPTR``
137 - 0x00000002 141 - 0x00000002
138 - This buffer type supports the ``V4L2_M 142 - This buffer type supports the ``V4L2_MEMORY_USERPTR`` streaming mode.
139 * - ``V4L2_BUF_CAP_SUPPORTS_DMABUF`` 143 * - ``V4L2_BUF_CAP_SUPPORTS_DMABUF``
140 - 0x00000004 144 - 0x00000004
141 - This buffer type supports the ``V4L2_M 145 - This buffer type supports the ``V4L2_MEMORY_DMABUF`` streaming mode.
142 * - ``V4L2_BUF_CAP_SUPPORTS_REQUESTS`` 146 * - ``V4L2_BUF_CAP_SUPPORTS_REQUESTS``
143 - 0x00000008 147 - 0x00000008
144 - This buffer type supports :ref:`reques 148 - This buffer type supports :ref:`requests <media-request-api>`.
145 * - ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS` 149 * - ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS``
146 - 0x00000010 150 - 0x00000010
147 - The kernel allows calling :ref:`VIDIOC 151 - The kernel allows calling :ref:`VIDIOC_REQBUFS` while buffers are still
148 mapped or exported via DMABUF. These o 152 mapped or exported via DMABUF. These orphaned buffers will be freed
149 when they are unmapped or when the exp 153 when they are unmapped or when the exported DMABUF fds are closed.
150 * - ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTU 154 * - ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF``
151 - 0x00000020 155 - 0x00000020
152 - Only valid for stateless decoders. If 156 - Only valid for stateless decoders. If set, then userspace can set the
153 ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` 157 ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag to hold off on returning the
154 capture buffer until the OUTPUT timest 158 capture buffer until the OUTPUT timestamp changes.
155 * - ``V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HIN <<
156 - 0x00000040 <<
157 - This capability is set by the driver t <<
158 cache and memory management hints. How <<
159 queue is used for :ref:`memory mapping <<
160 :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDAT <<
161 :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4 <<
162 :ref:`V4L2_MEMORY_FLAG_NON_COHERENT <V <<
163 * - ``V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFER <<
164 - 0x00000080 <<
165 - If set, then the ``max_num_buffers`` f <<
166 is valid. If not set, then the maximum <<
167 * - ``V4L2_BUF_CAP_SUPPORTS_REMOVE_BUFS`` <<
168 - 0x00000100 <<
169 - If set, then ``VIDIOC_REMOVE_BUFS`` is <<
170 <<
171 .. _memory-flags: <<
172 .. _V4L2-MEMORY-FLAG-NON-COHERENT: <<
173 <<
174 .. flat-table:: Memory Consistency Flags <<
175 :header-rows: 0 <<
176 :stub-columns: 0 <<
177 :widths: 3 1 4 <<
178 <<
179 * - ``V4L2_MEMORY_FLAG_NON_COHERENT`` <<
180 - 0x00000001 <<
181 - A buffer is allocated either in cohere <<
182 coherent between the CPU and the bus) <<
183 latter can provide performance gains, <<
184 sync/flush operations can be avoided i <<
185 corresponding device only and the CPU <<
186 buffer. However, this requires extra c <<
187 guarantee memory consistency by issuin <<
188 consistency is needed. If this flag is <<
189 allocate the buffer in non-coherent me <<
190 only if the buffer is used for :ref:`m <<
191 queue reports the :ref:`V4L2_BUF_CAP_S <<
192 <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINT <<
193 <<
194 .. raw:: latex <<
195 <<
196 \normalsize <<
197 159
198 Return Value 160 Return Value
199 ============ 161 ============
200 162
201 On success 0 is returned, on error -1 and the 163 On success 0 is returned, on error -1 and the ``errno`` variable is set
202 appropriately. The generic error codes are des 164 appropriately. The generic error codes are described at the
203 :ref:`Generic Error Codes <gen-errors>` chapte 165 :ref:`Generic Error Codes <gen-errors>` chapter.
204 166
205 EINVAL 167 EINVAL
206 The buffer type (``type`` field) or the re 168 The buffer type (``type`` field) or the requested I/O method
207 (``memory``) is not supported. 169 (``memory``) is not supported.
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