[deliverable/linux.git] / Documentation / linux_tv / media / v4l / vidioc-query-dv-timings.rst

.. -*- coding: utf-8; mode: rst -*-

.. _VIDIOC_QUERY_DV_TIMINGS:

*****************************
ioctl VIDIOC_QUERY_DV_TIMINGS
*****************************

*man VIDIOC_QUERY_DV_TIMINGS(2)*

VIDIOC_SUBDEV_QUERY_DV_TIMINGS
Sense the DV preset received by the current input


Synopsis
========

.. c:function:: int ioctl( int fd, int request, struct v4l2_dv_timings *argp )

Arguments
=========

``fd``
    File descriptor returned by :ref:`open() <func-open>`.

``request``
    VIDIOC_QUERY_DV_TIMINGS, VIDIOC_SUBDEV_QUERY_DV_TIMINGS

``argp``


Description
===========

The hardware may be able to detect the current DV timings automatically,
similar to sensing the video standard. To do so, applications call
:ref:`VIDIOC_QUERY_DV_TIMINGS` with a pointer to a struct
:ref:`v4l2_dv_timings <v4l2-dv-timings>`. Once the hardware detects
the timings, it will fill in the timings structure.

Please note that drivers shall *not* switch timings automatically if new
timings are detected. Instead, drivers should send the
``V4L2_EVENT_SOURCE_CHANGE`` event (if they support this) and expect
that userspace will take action by calling :ref:`VIDIOC_QUERY_DV_TIMINGS`.
The reason is that new timings usually mean different buffer sizes as
well, and you cannot change buffer sizes on the fly. In general,
applications that receive the Source Change event will have to call
:ref:`VIDIOC_QUERY_DV_TIMINGS`, and if the detected timings are valid they
will have to stop streaming, set the new timings, allocate new buffers
and start streaming again.

If the timings could not be detected because there was no signal, then
ENOLINK is returned. If a signal was detected, but it was unstable and
the receiver could not lock to the signal, then ENOLCK is returned. If
the receiver could lock to the signal, but the format is unsupported
(e.g. because the pixelclock is out of range of the hardware
capabilities), then the driver fills in whatever timings it could find
and returns ERANGE. In that case the application can call
:ref:`VIDIOC_DV_TIMINGS_CAP` to compare the
found timings with the hardware's capabilities in order to give more
precise feedback to the user.


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.

ENODATA
    Digital video timings are not supported for this input or output.

ENOLINK
    No timings could be detected because no signal was found.

ENOLCK
    The signal was unstable and the hardware could not lock on to it.

ERANGE
    Timings were found, but they are out of range of the hardware
    capabilities.


.. ------------------------------------------------------------------------------
.. This file was automatically converted from DocBook-XML with the dbxml
.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
.. from the linux kernel, refer to:
..
.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
.. ------------------------------------------------------------------------------
Commit	Line	Data
5377d91f MH	1	.. -- coding: utf-8; mode: rst --
5377d91f MH	2
af4a4d0d	3	.. _VIDIOC_QUERY_DV_TIMINGS:
5377d91f MH	4
	5	*****************************
	6	ioctl VIDIOC_QUERY_DV_TIMINGS
	7	*****************************
	8
	9	man VIDIOC_QUERY_DV_TIMINGS(2)
	10
	11	VIDIOC_SUBDEV_QUERY_DV_TIMINGS
	12	Sense the DV preset received by the current input
	13
	14
	15	Synopsis
	16	========
	17
	18	.. c:function:: int ioctl( int fd, int request, struct v4l2_dv_timings *argp )
	19
	20	Arguments
	21	=========
	22
	23	``fd``
	24	File descriptor returned by :ref:`open() <func-open>`.
	25
	26	``request``
	27	VIDIOC_QUERY_DV_TIMINGS, VIDIOC_SUBDEV_QUERY_DV_TIMINGS
	28
	29	``argp``
	30
	31
	32	Description
	33	===========
	34
	35	The hardware may be able to detect the current DV timings automatically,
	36	similar to sensing the video standard. To do so, applications call
2212ff25	37	:ref:`VIDIOC_QUERY_DV_TIMINGS` with a pointer to a struct
5377d91f MH	38	:ref:`v4l2_dv_timings <v4l2-dv-timings>`. Once the hardware detects
	39	the timings, it will fill in the timings structure.
	40
	41	Please note that drivers shall not switch timings automatically if new
	42	timings are detected. Instead, drivers should send the
	43	``V4L2_EVENT_SOURCE_CHANGE`` event (if they support this) and expect
2212ff25	44	that userspace will take action by calling :ref:`VIDIOC_QUERY_DV_TIMINGS`.
5377d91f MH	45	The reason is that new timings usually mean different buffer sizes as
	46	well, and you cannot change buffer sizes on the fly. In general,
	47	applications that receive the Source Change event will have to call
2212ff25	48	:ref:`VIDIOC_QUERY_DV_TIMINGS`, and if the detected timings are valid they
5377d91f MH	49	will have to stop streaming, set the new timings, allocate new buffers
	50	and start streaming again.
	51
	52	If the timings could not be detected because there was no signal, then
	53	ENOLINK is returned. If a signal was detected, but it was unstable and
	54	the receiver could not lock to the signal, then ENOLCK is returned. If
	55	the receiver could lock to the signal, but the format is unsupported
	56	(e.g. because the pixelclock is out of range of the hardware
	57	capabilities), then the driver fills in whatever timings it could find
	58	and returns ERANGE. In that case the application can call
7347081e	59	:ref:`VIDIOC_DV_TIMINGS_CAP` to compare the
5377d91f MH	60	found timings with the hardware's capabilities in order to give more
	61	precise feedback to the user.
	62
	63
	64	Return Value
	65	============
	66
	67	On success 0 is returned, on error -1 and the ``errno`` variable is set
	68	appropriately. The generic error codes are described at the
	69	:ref:`Generic Error Codes <gen-errors>` chapter.
	70
	71	ENODATA
	72	Digital video timings are not supported for this input or output.
	73
	74	ENOLINK
	75	No timings could be detected because no signal was found.
	76
	77	ENOLCK
	78	The signal was unstable and the hardware could not lock on to it.
	79
	80	ERANGE
	81	Timings were found, but they are out of range of the hardware
	82	capabilities.
	83
	84
	85	.. ------------------------------------------------------------------------------
	86	.. This file was automatically converted from DocBook-XML with the dbxml
	87	.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
	88	.. from the linux kernel, refer to:
	89	..
	90	.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
	91	.. ------------------------------------------------------------------------------