linux/Documentation/media/v4l-drivers/vimc.rst

.. SPDX-License-Identifier: GPL-2.0

The Virtual Media Controller Driver (vimc)
==========================================

The vimc driver emulates complex video hardware using the V4L2 API and the Media
API. It has a capture device and three subdevices: sensor, debayer and scaler.

Topology
--------

The topology is hardcoded, although you could modify it in vimc-core and
recompile the driver to achieve your own topology. This is the default topology:

.. _vimc_topology_graph:

.. kernel-figure:: vimc.dot
    :alt:   vimc.dot
    :align: center

    Media pipeline graph on vimc

Configuring the topology
~~~~~~~~~~~~~~~~~~~~~~~~

Each subdevice will come with its default configuration (pixelformat, height,
width, ...). One needs to configure the topology in order to match the
configuration on each linked subdevice to stream frames through the pipeline.
If the configuration doesn't match, the stream will fail. The ``v4l-utils``
package is a bundle of user-space applications, that comes with ``media-ctl`` and
``v4l2-ctl`` that can be used to configure the vimc configuration. This sequence
of commands fits for the default topology:

.. code-block:: bash

        media-ctl -d platform:vimc -V '"Sensor A":0[fmt:SBGGR8_1X8/640x480]'
        media-ctl -d platform:vimc -V '"Debayer A":0[fmt:SBGGR8_1X8/640x480]'
        media-ctl -d platform:vimc -V '"Sensor B":0[fmt:SBGGR8_1X8/640x480]'
        media-ctl -d platform:vimc -V '"Debayer B":0[fmt:SBGGR8_1X8/640x480]'
        v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=1920,height=1440
        v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v pixelformat=BA81
        v4l2-ctl -z platform:vimc -d "Raw Capture 1" -v pixelformat=BA81

Subdevices
----------

Subdevices define the behavior of an entity in the topology. Depending on the
subdevice, the entity can have multiple pads of type source or sink.

vimc-sensor:
	Generates images in several formats using video test pattern generator.
	Exposes:

	* 1 Pad source

vimc-debayer:
	Transforms images in bayer format into a non-bayer format.
	Exposes:

	* 1 Pad sink
	* 1 Pad source

vimc-scaler:
	Scale up the image by a factor of 3. E.g.: a 640x480 image becomes a
        1920x1440 image. (this value can be configured, see at
        `Module options`_).
	Exposes:

	* 1 Pad sink
	* 1 Pad source

vimc-capture:
	Exposes node /dev/videoX to allow userspace to capture the stream.
	Exposes:

	* 1 Pad sink
	* 1 Pad source

Module options
---------------

Vimc has a few module parameters to configure the driver. You should pass
those arguments to each subdevice, not to the vimc module. For example::

        vimc_subdevice.param=value

* ``vimc_scaler.sca_mult=<unsigned int>``

        Image size multiplier factor to be used to multiply both width and
        height, so the image size will be ``sca_mult^2`` bigger than the
        original one. Currently, only supports scaling up (the default value
        is 3).

* ``vimc_debayer.deb_mean_win_size=<unsigned int>``

        Window size to calculate the mean. Note: the window size needs to be an
        odd number, as the main pixel stays in the center of the window,
        otherwise the next odd number is considered (the default value is 3).