mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-22 04:03:58 +08:00
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>
84 lines
2.8 KiB
ReStructuredText
84 lines
2.8 KiB
ReStructuredText
.. Permission is granted to copy, distribute and/or modify this
|
|
.. document under the terms of the GNU Free Documentation License,
|
|
.. Version 1.1 or any later version published by the Free Software
|
|
.. Foundation, with no Invariant Sections, no Front-Cover Texts
|
|
.. and no Back-Cover Texts. A copy of the license is included at
|
|
.. Documentation/userspace-api/media/fdl-appendix.rst.
|
|
..
|
|
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
|
|
|
|
.. _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:function:: int ioctl( int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp )
|
|
:name: DMX_REQBUFS
|
|
|
|
|
|
Arguments
|
|
=========
|
|
|
|
``fd``
|
|
File descriptor returned by :ref:`open() <dmx_fopen>`.
|
|
|
|
``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.
|