1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: DTV.dmx 2 .. c:namespace:: DTV.dmx
3 3
4 .. _DMX_REQBUFS: 4 .. _DMX_REQBUFS:
5 5
6 ***************** 6 *****************
7 ioctl DMX_REQBUFS 7 ioctl DMX_REQBUFS
8 ***************** 8 *****************
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 DMX_REQBUFS - Initiate Memory Mapping and/or D 13 DMX_REQBUFS - Initiate Memory Mapping and/or DMA buffer I/O
14 14
15 .. warning:: this API is still experimental 15 .. warning:: this API is still experimental
16 16
17 Synopsis 17 Synopsis
18 ======== 18 ========
19 19
20 .. c:macro:: DMX_REQBUFS 20 .. c:macro:: DMX_REQBUFS
21 21
22 ``int ioctl(int fd, DMX_REQBUFS, struct dmx_re 22 ``int ioctl(int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp)``
23 23
24 Arguments 24 Arguments
25 ========= 25 =========
26 26
27 ``fd`` 27 ``fd``
28 File descriptor returned by :c:func:`open( 28 File descriptor returned by :c:func:`open()`.
29 29
30 ``argp`` 30 ``argp``
31 Pointer to struct :c:type:`dmx_requestbuff 31 Pointer to struct :c:type:`dmx_requestbuffers`.
32 32
33 Description 33 Description
34 =========== 34 ===========
35 35
36 This ioctl is used to initiate a memory mapped 36 This ioctl is used to initiate a memory mapped or DMABUF based demux I/O.
37 37
38 Memory mapped buffers are located in device me 38 Memory mapped buffers are located in device memory and must be allocated
39 with this ioctl before they can be mapped into 39 with this ioctl before they can be mapped into the application's address
40 space. User buffers are allocated by applicati 40 space. User buffers are allocated by applications themselves, and this
41 ioctl is merely used to switch the driver into 41 ioctl is merely used to switch the driver into user pointer I/O mode and
42 to setup some internal structures. Similarly, 42 to setup some internal structures. Similarly, DMABUF buffers are
43 allocated by applications through a device dri 43 allocated by applications through a device driver, and this ioctl only
44 configures the driver into DMABUF I/O mode wit 44 configures the driver into DMABUF I/O mode without performing any direct
45 allocation. 45 allocation.
46 46
47 To allocate device buffers applications initia 47 To allocate device buffers applications initialize all fields of the
48 struct :c:type:`dmx_requestbuffers` structure. 48 struct :c:type:`dmx_requestbuffers` structure. They set the ``count`` field
49 to the desired number of buffers, and ``size` 49 to the desired number of buffers, and ``size`` to the size of each
50 buffer. 50 buffer.
51 51
52 When the ioctl is called with a pointer to thi 52 When the ioctl is called with a pointer to this structure, the driver will
53 attempt to allocate the requested number of bu 53 attempt to allocate the requested number of buffers and it stores the actual
54 number allocated in the ``count`` field. The ` 54 number allocated in the ``count`` field. The ``count`` can be smaller than the number requested, even zero, when the driver runs out of free memory. A larger
55 number is also possible when the driver requir 55 number is also possible when the driver requires more buffers to
56 function correctly. The actual allocated buffe 56 function correctly. The actual allocated buffer size can is returned
57 at ``size``, and can be smaller than what's re 57 at ``size``, and can be smaller than what's requested.
58 58
59 When this I/O method is not supported, the ioc 59 When this I/O method is not supported, the ioctl returns an ``EOPNOTSUPP``
60 error code. 60 error code.
61 61
62 Applications can call :ref:`DMX_REQBUFS` again 62 Applications can call :ref:`DMX_REQBUFS` again to change the number of
63 buffers, however this cannot succeed when any 63 buffers, however this cannot succeed when any buffers are still mapped.
64 A ``count`` value of zero frees all buffers, a 64 A ``count`` value of zero frees all buffers, after aborting or finishing
65 any DMA in progress. 65 any DMA in progress.
66 66
67 Return Value 67 Return Value
68 ============ 68 ============
69 69
70 On success 0 is returned, on error -1 and the 70 On success 0 is returned, on error -1 and the ``errno`` variable is set
71 appropriately. The generic error codes are des 71 appropriately. The generic error codes are described at the
72 :ref:`Generic Error Codes <gen-errors>` chapte 72 :ref:`Generic Error Codes <gen-errors>` chapter.
73 73
74 EOPNOTSUPP 74 EOPNOTSUPP
75 The the requested I/O method is not suppo 75 The the requested I/O method is not supported.
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