1.. SPDX-License-Identifier: GPL-2.0
2
3The Virtual Media Controller Driver (vimc)
4==========================================
5
6The vimc driver emulates complex video hardware using the V4L2 API and the Media
7API. It has a capture device and three subdevices: sensor, debayer and scaler.
8
9Topology
10--------
11
12The topology is hardcoded, although you could modify it in vimc-core and
13recompile the driver to achieve your own topology. This is the default topology:
14
15.. _vimc_topology_graph:
16
17.. kernel-figure:: vimc.dot
18    :alt:   Diagram of the default media pipeline topology
19    :align: center
20
21    Media pipeline graph on vimc
22
23Configuring the topology
24~~~~~~~~~~~~~~~~~~~~~~~~
25
26Each subdevice will come with its default configuration (pixelformat, height,
27width, ...). One needs to configure the topology in order to match the
28configuration on each linked subdevice to stream frames through the pipeline.
29If the configuration doesn't match, the stream will fail. The ``v4l-utils``
30package is a bundle of user-space applications, that comes with ``media-ctl`` and
31``v4l2-ctl`` that can be used to configure the vimc configuration. This sequence
32of commands fits for the default topology:
33
34.. code-block:: bash
35
36        media-ctl -d platform:vimc -V '"Sensor A":0[fmt:SBGGR8_1X8/640x480]'
37        media-ctl -d platform:vimc -V '"Debayer A":0[fmt:SBGGR8_1X8/640x480]'
38        media-ctl -d platform:vimc -V '"Sensor B":0[fmt:SBGGR8_1X8/640x480]'
39        media-ctl -d platform:vimc -V '"Debayer B":0[fmt:SBGGR8_1X8/640x480]'
40        v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=1920,height=1440
41        v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v pixelformat=BA81
42        v4l2-ctl -z platform:vimc -d "Raw Capture 1" -v pixelformat=BA81
43
44Subdevices
45----------
46
47Subdevices define the behavior of an entity in the topology. Depending on the
48subdevice, the entity can have multiple pads of type source or sink.
49
50vimc-sensor:
51	Generates images in several formats using video test pattern generator.
52	Exposes:
53
54	* 1 Pad source
55
56vimc-debayer:
57	Transforms images in bayer format into a non-bayer format.
58	Exposes:
59
60	* 1 Pad sink
61	* 1 Pad source
62
63vimc-scaler:
64	Scale up the image by a factor of 3. E.g.: a 640x480 image becomes a
65        1920x1440 image. (this value can be configured, see at
66        `Module options`_).
67	Exposes:
68
69	* 1 Pad sink
70	* 1 Pad source
71
72vimc-capture:
73	Exposes node /dev/videoX to allow userspace to capture the stream.
74	Exposes:
75
76	* 1 Pad sink
77	* 1 Pad source
78
79
80Module options
81--------------
82
83Vimc has a module parameter to configure the driver.
84
85* ``sca_mult=<unsigned int>``
86
87        Image size multiplier factor to be used to multiply both width and
88        height, so the image size will be ``sca_mult^2`` bigger than the
89        original one. Currently, only supports scaling up (the default value
90        is 3).
91