OpenE2K
/
linux
6
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

media: dvb uAPI docs: document mmap-related ioctls 

5 new ioctls were added to the DVB demux API, in order to
handle memory maped I/O. Add documentation for them.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Mauro Carvalho Chehab 2017-12-21 10:42:26 -05:00
parent f8aaf48771
commit a1f18fdc72
5 changed files with 320 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

90
Documentation/media/uapi/dvb/dmx-expbuf.rst Normal file
View File

@ -0,0 +1,90 @@
.. _DMX_EXPBUF:
****************
ioctl DMX_EXPBUF
****************
Name
====
DMX_EXPBUF - Export a buffer as a DMABUF file descriptor.
.. warning:: this API is still experimental
Synopsis
========
.. c:function:: int ioctl( int fd, DMX_EXPBUF, struct dmx_exportbuffer *argp )
:name: DMX_EXPBUF
Arguments
=========
``fd``
File descriptor returned by :ref:`open() <dmx_fopen>`.
``argp``
Pointer to struct :c:type:`dmx_exportbuffer`.
Description
===========
This ioctl is an extension to the memory mapping I/O method.
It can be used to export a buffer as a DMABUF file at any time after
buffers have been allocated with the :ref:`DMX_REQBUFS` ioctl.
The ``reserved`` array must be zeroed before calling it.
To export a buffer, applications fill struct :c:type:`dmx_exportbuffer`.
Applications must set the ``index`` field. Valid index numbers
range from zero to the number of buffers allocated with :ref:`DMX_REQBUFS`
(struct :c:type:`dmx_requestbuffers` ``count``) minus one.
Additional flags may be posted in the ``flags`` field. Refer to a manual
for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
and O_RDWR are supported.
All other fields must be set to zero. In the
case of multi-planar API, every plane is exported separately using
multiple :ref:`DMX_EXPBUF` calls.
After calling :ref:`DMX_EXPBUF` the ``fd`` field will be set by a
driver, on success. This is a DMABUF file descriptor. The application may
pass it to other DMABUF-aware devices. It is recommended to close a DMABUF
file when it is no longer used to allow the associated memory to be reclaimed.
Examples
========
.. code-block:: c
int buffer_export(int v4lfd, enum dmx_buf_type bt, int index, int *dmafd)
{
struct dmx_exportbuffer expbuf;
memset(&expbuf, 0, sizeof(expbuf));
expbuf.type = bt;
expbuf.index = index;
if (ioctl(v4lfd, DMX_EXPBUF, &expbuf) == -1) {
perror("DMX_EXPBUF");
return -1;
}
*dmafd = expbuf.fd;
return 0;
}
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.
EINVAL
A queue is not in MMAP mode or DMABUF exporting is not supported or
``flags`` or ``index`` fields are invalid.

85
Documentation/media/uapi/dvb/dmx-qbuf.rst Normal file
View File

@ -0,0 +1,85 @@
.. _DMX_QBUF:
*************************
ioctl DMX_QBUF, DMX_DQBUF
*************************
Name
====
DMX_QBUF - DMX_DQBUF - Exchange a buffer with the driver
.. warning:: this API is still experimental
Synopsis
========
.. c:function:: int ioctl( int fd, DMX_QBUF, struct dmx_buffer *argp )
:name: DMX_QBUF
.. c:function:: int ioctl( int fd, DMX_DQBUF, struct dmx_buffer *argp )
:name: DMX_DQBUF
Arguments
=========
``fd``
File descriptor returned by :ref:`open() <dmx_fopen>`.
``argp``
Pointer to struct :c:type:`dmx_buffer`.
Description
===========
Applications call the ``DMX_QBUF`` ioctl to enqueue an empty
(capturing) or filled (output) buffer in the driver's incoming queue.
The semantics depend on the selected I/O method.
To enqueue a buffer applications set the ``index`` field. Valid index
numbers range from zero to the number of buffers allocated with
:ref:`DMX_REQBUFS` (struct :c:type:`dmx_requestbuffers` ``count``) minus
one. The contents of the struct :c:type:`dmx_buffer` returned
by a :ref:`DMX_QUERYBUF` ioctl will do as well.
The and ``reserved`` field must be set to 0.
When ``DMX_QBUF`` is called with a pointer to this structure, it locks the
memory pages of the buffer in physical memory, so they cannot be swapped
out to disk. Buffers remain locked until dequeued, until the
the device is closed.
Applications call the ``DMX_DQBUF`` ioctl to dequeue a filled
(capturing) buffer from the driver's outgoing queue. They just set the ``reserved`` field array to zero. When ``DMX_DQBUF`` is called with a
pointer to this structure, the driver fills the remaining fields or
returns an error code.
By default ``DMX_DQBUF`` blocks when no buffer is in the outgoing
queue. When the ``O_NONBLOCK`` flag was given to the
:ref:`open() <dmx_fopen>` function, ``DMX_DQBUF`` returns
immediately with an ``EAGAIN`` error code when no buffer is available.
The struct :c:type:`dmx_buffer` structure is specified in
:ref:`buffer`.
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.
EAGAIN
Non-blocking I/O has been selected using ``O_NONBLOCK`` and no
buffer was in the outgoing queue.
EINVAL
The ``index`` is out of bounds, or no buffers have been allocated yet.
EIO
``DMX_DQBUF`` failed due to an internal error. Can also indicate
temporary problems like signal loss or CRC errors.

65
Documentation/media/uapi/dvb/dmx-querybuf.rst Normal file
View File

@ -0,0 +1,65 @@
.. _DMX_QUERYBUF:
******************
ioctl DMX_QUERYBUF
******************
Name
====
DMX_QUERYBUF - Query the status of a buffer
.. warning:: this API is still experimental
Synopsis
========
.. c:function:: int ioctl( int fd, DMX_QUERYBUF, struct dvb_buffer *argp )
:name: DMX_QUERYBUF
Arguments
=========
``fd``
File descriptor returned by :ref:`open() <dmx_fopen>`.
``argp``
Pointer to struct :c:type:`dvb_buffer`.
Description
===========
This ioctl is part of the mmap streaming I/O method. It can
be used to query the status of a buffer at any time after buffers have
been allocated with the :ref:`DMX_REQBUFS` ioctl.
The ``reserved`` array must be zeroed before calling it.
Applications set the ``index`` field. Valid index numbers range from zero
to the number of buffers allocated with :ref:`DMX_REQBUFS`
(struct :c:type:`dvb_requestbuffers` ``count``) minus one.
After calling :ref:`DMX_QUERYBUF` with a pointer to this structure,
drivers return an error code or fill the rest of the structure.
On success, the ``offset`` will contain the offset of the buffer from the
start of the device memory, the ``length`` field its size, and the
``bytesused`` the number of bytes occupied by data in the buffer (payload).
Return Value
============
On success 0 is returned, the ``offset`` will contain the offset of the
buffer from the start of the device memory, the ``length`` field its size,
and the ``bytesused`` the number of bytes occupied by data in the buffer
(payload).
On error it returns -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.
EINVAL
The ``index`` is out of bounds.

76
Documentation/media/uapi/dvb/dmx-reqbufs.rst Normal file
View File

@ -0,0 +1,76 @@
.. _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.
The ``reserved`` array must be zeroed before calling it.
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.

4
Documentation/media/uapi/dvb/dmx_fcalls.rst
View File

@ -24,3 +24,7 @@ Demux Function Calls
dmx-get-pes-pids
dmx-add-pid
dmx-remove-pid
dmx-reqbufs
dmx-querybuf
dmx-expbuf
dmx-qbuf