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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/userspace-api/media/dvb/dmx-reqbufs.rst | |
parent | Initial commit. (diff) | |
download | linux-430c2fc249ea5c0536abd21c23382884005c9093.tar.xz linux-430c2fc249ea5c0536abd21c23382884005c9093.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/userspace-api/media/dvb/dmx-reqbufs.rst')
-rw-r--r-- | Documentation/userspace-api/media/dvb/dmx-reqbufs.rst | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/dvb/dmx-reqbufs.rst b/Documentation/userspace-api/media/dvb/dmx-reqbufs.rst new file mode 100644 index 000000000..d2bb1909e --- /dev/null +++ b/Documentation/userspace-api/media/dvb/dmx-reqbufs.rst @@ -0,0 +1,75 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: DTV.dmx + +.. _DMX_REQBUFS: + +***************** +ioctl DMX_REQBUFS +***************** + +Name +==== + +DMX_REQBUFS - Initiate Memory Mapping and/or DMA buffer I/O + +.. warning:: this API is still experimental + +Synopsis +======== + +.. c:macro:: DMX_REQBUFS + +``int ioctl(int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp)`` + +Arguments +========= + +``fd`` + File descriptor returned by :c:func:`open()`. + +``argp`` + Pointer to struct :c:type:`dmx_requestbuffers`. + +Description +=========== + +This ioctl is used to initiate a memory mapped or DMABUF based demux I/O. + +Memory mapped buffers are located in device memory and must be allocated +with this ioctl before they can be mapped into the application's address +space. User buffers are allocated by applications themselves, and this +ioctl is merely used to switch the driver into user pointer I/O mode and +to setup some internal structures. Similarly, DMABUF buffers are +allocated by applications through a device driver, and this ioctl only +configures the driver into DMABUF I/O mode without performing any direct +allocation. + +To allocate device buffers applications initialize all fields of the +struct :c:type:`dmx_requestbuffers` structure. They set the ``count`` field +to the desired number of buffers, and ``size`` to the size of each +buffer. + +When the ioctl is called with a pointer to this structure, the driver will +attempt to allocate the requested number of buffers and it stores the actual +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 +number is also possible when the driver requires more buffers to +function correctly. The actual allocated buffer size can is returned +at ``size``, and can be smaller than what's requested. + +When this I/O method is not supported, the ioctl returns an ``EOPNOTSUPP`` +error code. + +Applications can call :ref:`DMX_REQBUFS` again to change the number of +buffers, however this cannot succeed when any buffers are still mapped. +A ``count`` value of zero frees all buffers, after aborting or finishing +any DMA in progress. + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. + +EOPNOTSUPP + The the requested I/O method is not supported. |