147 lines
4.7 KiB
ReStructuredText
147 lines
4.7 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
|
|
|
|
.. _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:function:: int ioctl( int fd, VIDIOC_SUBDEV_G_FMT, struct v4l2_subdev_format *argp )
|
|
:name: VIDIOC_SUBDEV_G_FMT
|
|
|
|
.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_S_FMT, struct v4l2_subdev_format *argp )
|
|
:name: VIDIOC_SUBDEV_S_FMT
|
|
|
|
|
|
Arguments
|
|
=========
|
|
|
|
``fd``
|
|
File descriptor returned by :ref:`open() <func-open>`.
|
|
|
|
``argp``
|
|
|
|
|
|
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,
|
|
a low-pass noise filter might crop pixels at the frame boundaries,
|
|
modifying its output frame size.
|
|
|
|
Drivers must not return an error solely because the requested format
|
|
doesn't match the device capabilities. They must instead modify the
|
|
format to match what the hardware can provide. The modified format
|
|
should be as close as possible to the original request.
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. c:type:: v4l2_subdev_format
|
|
|
|
.. flat-table:: struct v4l2_subdev_format
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - __u32
|
|
- ``pad``
|
|
- Pad number as reported by the media controller API.
|
|
* - __u32
|
|
- ``which``
|
|
- Format to modified, from enum
|
|
:ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
|
|
* - struct :c:type:`v4l2_mbus_framefmt`
|
|
- ``format``
|
|
- Definition of an image format, see :c:type:`v4l2_mbus_framefmt` for
|
|
details.
|
|
* - __u32
|
|
- ``reserved``\ [8]
|
|
- Reserved for future extensions. Applications and drivers must set
|
|
the array to zero.
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
|
|
|
|
.. _v4l2-subdev-format-whence:
|
|
|
|
.. flat-table:: enum v4l2_subdev_format_whence
|
|
:header-rows: 0
|
|
:stub-columns: 0
|
|
:widths: 3 1 4
|
|
|
|
* - V4L2_SUBDEV_FORMAT_TRY
|
|
- 0
|
|
- Try formats, used for querying device capabilities.
|
|
* - V4L2_SUBDEV_FORMAT_ACTIVE
|
|
- 1
|
|
- Active formats, applied to the hardware.
|
|
|
|
|
|
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.
|
|
|
|
EBUSY
|
|
The format can't be changed because the pad is currently busy. This
|
|
can be caused, for instance, by an active video stream on the pad.
|
|
The ioctl must not be retried without performing another action to
|
|
fix the problem first. Only returned by ``VIDIOC_SUBDEV_S_FMT``
|
|
|
|
EINVAL
|
|
The struct :c:type:`v4l2_subdev_format`
|
|
``pad`` references a non-existing pad, or the ``which`` field
|
|
references a non-existing format.
|
|
|
|
|
|
============
|
|
|
|
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.
|