Documentation/userspace-api/media/v4l/vidioc-query-dv-timings.rst

Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/v4l/vidioc-query-dv-timings.rst

File Facts

System
Linux kernel
Corpus path
Documentation/userspace-api/media/v4l/vidioc-query-dv-timings.rst
Extension
.rst
Size
2881 bytes
Lines
87
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: documentation
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L

.. _VIDIOC_QUERY_DV_TIMINGS:

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

Name
====

VIDIOC_QUERY_DV_TIMINGS - VIDIOC_SUBDEV_QUERY_DV_TIMINGS - Sense the DV preset received by the current input

Synopsis
========

.. c:macro:: VIDIOC_QUERY_DV_TIMINGS

``int ioctl(int fd, VIDIOC_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)``

.. c:macro:: VIDIOC_SUBDEV_QUERY_DV_TIMINGS

``int ioctl(int fd, VIDIOC_SUBDEV_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)``

Arguments
=========

``fd``
    File descriptor returned by :c:func:`open()`.

``argp``
    Pointer to struct :c:type:`v4l2_dv_timings`.

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
:c:type:`v4l2_dv_timings`. Once the hardware detects
the timings, it will fill in the timings structure.

.. note::

   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
============

Annotation

Implementation Notes