media: docs: create vimc documentation

Create vimc documentation file to explain its basic features, its
topology, how to configure it and to document vimc's subdevices.
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Suggested-by: Helen Koike <helen.koike@collabora.com>
[hverkuil-cisco@xs4all.nl: Fix typo: The ``v4l2-utils`` -> The ``v4l-utils`` package]
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/v4l-drivers/index.rst

@@ -64,5 +64,6 @@ For more details see the file COPYING in the source distribution of Linux.
 	si476x
 	soc-camera
 	uvcvideo
+	vimc
 	vivid
 	zr364xx

Documentation/media/v4l-drivers/vimc.dot

+# SPDX-License-Identifier: GPL-2.0
+
+digraph board {
+	rankdir=TB
+	n00000001 [label="{{} | Sensor A\n/dev/v4l-subdev0 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000001:port0 -> n00000005:port0 [style=bold]
+	n00000001:port0 -> n0000000b [style=bold]
+	n00000003 [label="{{} | Sensor B\n/dev/v4l-subdev1 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000003:port0 -> n00000008:port0 [style=bold]
+	n00000003:port0 -> n0000000f [style=bold]
+	n00000005 [label="{{<port0> 0} | Debayer A\n/dev/v4l-subdev2 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000005:port1 -> n00000017:port0
+	n00000008 [label="{{<port0> 0} | Debayer B\n/dev/v4l-subdev3 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000008:port1 -> n00000017:port0 [style=dashed]
+	n0000000b [label="Raw Capture 0\n/dev/video0", shape=box, style=filled, fillcolor=yellow]
+	n0000000f [label="Raw Capture 1\n/dev/video1", shape=box, style=filled, fillcolor=yellow]
+	n00000013 [label="RGB/YUV Input\n/dev/video2", shape=box, style=filled, fillcolor=yellow]
+	n00000013 -> n00000017:port0 [style=dashed]
+	n00000017 [label="{{<port0> 0} | Scaler\n/dev/v4l-subdev4 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000017:port1 -> n0000001a [style=bold]
+	n0000001a [label="RGB/YUV Capture\n/dev/video3", shape=box, style=filled, fillcolor=yellow]
+}

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).