Documentation/userspace-api/media/v4l/vidioc-subdev-g-fmt.rst

Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/v4l/vidioc-subdev-g-fmt.rst

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Linux kernel
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Documentation/userspace-api/media/v4l/vidioc-subdev-g-fmt.rst
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.rst
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Support Tooling And Documentation
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Documentation
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Support Tooling And Documentation: documentation
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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Annotated Snippet

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

.. _VIDIOC_SUBDEV_G_FMT:

**********************************************
ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT
**********************************************

Name
====

VIDIOC_SUBDEV_G_FMT - VIDIOC_SUBDEV_S_FMT - Get or set the data format on a subdev pad

Synopsis
========

.. c:macro:: VIDIOC_SUBDEV_G_FMT

``int ioctl(int fd, VIDIOC_SUBDEV_G_FMT, struct v4l2_subdev_format *argp)``

.. c:macro:: VIDIOC_SUBDEV_S_FMT

``int ioctl(int fd, VIDIOC_SUBDEV_S_FMT, struct v4l2_subdev_format *argp)``

Arguments
=========

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

``argp``
    Pointer to struct :c:type:`v4l2_subdev_format`.

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

These ioctls are used to negotiate the frame format at specific subdev
pads in the image pipeline.

To retrieve the current format applications set the ``pad`` field of a
struct :c:type:`v4l2_subdev_format` to the desired
pad number as reported by the media API and the ``which`` field to
``V4L2_SUBDEV_FORMAT_ACTIVE``. When they call the
``VIDIOC_SUBDEV_G_FMT`` ioctl with a pointer to this structure the
driver fills the members of the ``format`` field.

To change the current format applications set both the ``pad`` and
``which`` fields and all members of the ``format`` field. When they call
the ``VIDIOC_SUBDEV_S_FMT`` ioctl with a pointer to this structure the
driver verifies the requested format, adjusts it based on the hardware
capabilities and configures the device. Upon return the struct
:c:type:`v4l2_subdev_format` contains the current
format as would be returned by a ``VIDIOC_SUBDEV_G_FMT`` call.

Applications can query the device capabilities by setting the ``which``
to ``V4L2_SUBDEV_FORMAT_TRY``. When set, 'try' formats are not applied
to the device by the driver, but are changed exactly as active formats
and stored in the sub-device file handle. Two applications querying the
same sub-device would thus not interact with each other.

For instance, to try a format at the output pad of a sub-device,
applications would first set the try format at the sub-device input with
the ``VIDIOC_SUBDEV_S_FMT`` ioctl. They would then either retrieve the
default format at the output pad with the ``VIDIOC_SUBDEV_G_FMT`` ioctl,
or set the desired output pad format with the ``VIDIOC_SUBDEV_S_FMT``
ioctl and check the returned value.

Try formats do not depend on active formats, but can depend on the
current links configuration or sub-device controls value. For instance,

Annotation

Implementation Notes