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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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54f38fcae5
Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee38 ("docs: Create a user-space API guide").
As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.
Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
98 lines
2.7 KiB
ReStructuredText
98 lines
2.7 KiB
ReStructuredText
.. Permission is granted to copy, distribute and/or modify this
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.. document under the terms of the GNU Free Documentation License,
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.. Version 1.1 or any later version published by the Free Software
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.. Foundation, with no Invariant Sections, no Front-Cover Texts
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.. and no Back-Cover Texts. A copy of the license is included at
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.. Documentation/userspace-api/media/fdl-appendix.rst.
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..
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.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
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.. _DMX_EXPBUF:
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****************
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ioctl DMX_EXPBUF
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****************
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Name
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====
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DMX_EXPBUF - Export a buffer as a DMABUF file descriptor.
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.. warning:: this API is still experimental
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Synopsis
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========
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.. c:function:: int ioctl( int fd, DMX_EXPBUF, struct dmx_exportbuffer *argp )
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:name: DMX_EXPBUF
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <dmx_fopen>`.
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``argp``
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Pointer to struct :c:type:`dmx_exportbuffer`.
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Description
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===========
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This ioctl is an extension to the memory mapping I/O method.
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It can be used to export a buffer as a DMABUF file at any time after
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buffers have been allocated with the :ref:`DMX_REQBUFS` ioctl.
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To export a buffer, applications fill struct :c:type:`dmx_exportbuffer`.
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Applications must set the ``index`` field. Valid index numbers
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range from zero to the number of buffers allocated with :ref:`DMX_REQBUFS`
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(struct :c:type:`dmx_requestbuffers` ``count``) minus one.
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Additional flags may be posted in the ``flags`` field. Refer to a manual
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for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
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and O_RDWR are supported.
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All other fields must be set to zero. In the
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case of multi-planar API, every plane is exported separately using
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multiple :ref:`DMX_EXPBUF` calls.
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After calling :ref:`DMX_EXPBUF` the ``fd`` field will be set by a
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driver, on success. This is a DMABUF file descriptor. The application may
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pass it to other DMABUF-aware devices. It is recommended to close a DMABUF
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file when it is no longer used to allow the associated memory to be reclaimed.
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Examples
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========
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.. code-block:: c
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int buffer_export(int v4lfd, enum dmx_buf_type bt, int index, int *dmafd)
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{
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struct dmx_exportbuffer expbuf;
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memset(&expbuf, 0, sizeof(expbuf));
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expbuf.type = bt;
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expbuf.index = index;
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if (ioctl(v4lfd, DMX_EXPBUF, &expbuf) == -1) {
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perror("DMX_EXPBUF");
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return -1;
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}
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*dmafd = expbuf.fd;
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return 0;
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}
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EINVAL
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A queue is not in MMAP mode or DMABUF exporting is not supported or
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``flags`` or ``index`` fields are invalid.
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