111 lines
3.3 KiB
ReStructuredText
111 lines
3.3 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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The Virtual Media Controller Driver (vimc)
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==========================================
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The vimc driver emulates complex video hardware using the V4L2 API and the Media
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API. It has a capture device and three subdevices: sensor, debayer and scaler.
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Topology
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--------
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The topology is hardcoded, although you could modify it in vimc-core and
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recompile the driver to achieve your own topology. This is the default topology:
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.. _vimc_topology_graph:
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.. kernel-figure:: vimc.dot
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:alt: Diagram of the default media pipeline topology
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:align: center
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Media pipeline graph on vimc
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Configuring the topology
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~~~~~~~~~~~~~~~~~~~~~~~~
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Each subdevice will come with its default configuration (pixelformat, height,
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width, ...). One needs to configure the topology in order to match the
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configuration on each linked subdevice to stream frames through the pipeline.
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If the configuration doesn't match, the stream will fail. The ``v4l-utils``
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package is a bundle of user-space applications, that comes with ``media-ctl`` and
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``v4l2-ctl`` that can be used to configure the vimc configuration. This sequence
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of commands fits for the default topology:
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.. code-block:: bash
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media-ctl -d platform:vimc -V '"Sensor A":0[fmt:SBGGR8_1X8/640x480]'
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media-ctl -d platform:vimc -V '"Debayer A":0[fmt:SBGGR8_1X8/640x480]'
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media-ctl -d platform:vimc -V '"Scaler":0[fmt:RGB888_1X24/640x480]'
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media-ctl -d platform:vimc -V '"Scaler":0[crop:(100,50)/400x150]'
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media-ctl -d platform:vimc -V '"Scaler":1[fmt:RGB888_1X24/300x700]'
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v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=300,height=700
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v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v pixelformat=BA81
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Subdevices
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----------
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Subdevices define the behavior of an entity in the topology. Depending on the
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subdevice, the entity can have multiple pads of type source or sink.
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vimc-sensor:
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Generates images in several formats using video test pattern generator.
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Exposes:
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* 1 Pad source
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vimc-lens:
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Ancillary lens for a sensor. Supports auto focus control. Linked to
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a vimc-sensor using an ancillary link. The lens supports FOCUS_ABSOLUTE
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control.
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.. code-block:: bash
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media-ctl -p
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...
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- entity 28: Lens A (0 pad, 0 link)
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type V4L2 subdev subtype Lens flags 0
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device node name /dev/v4l-subdev6
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- entity 29: Lens B (0 pad, 0 link)
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type V4L2 subdev subtype Lens flags 0
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device node name /dev/v4l-subdev7
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v4l2-ctl -d /dev/v4l-subdev7 -C focus_absolute
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focus_absolute: 0
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vimc-debayer:
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Transforms images in bayer format into a non-bayer format.
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Exposes:
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* 1 Pad sink
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* 1 Pad source
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vimc-scaler:
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Re-size the image to meet the source pad resolution. E.g.: if the sync
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pad is configured to 360x480 and the source to 1280x720, the image will
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be stretched to fit the source resolution. Works for any resolution
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within the vimc limitations (even shrinking the image if necessary).
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Exposes:
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* 1 Pad sink
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* 1 Pad source
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vimc-capture:
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Exposes node /dev/videoX to allow userspace to capture the stream.
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Exposes:
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* 1 Pad sink
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* 1 Pad source
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Module options
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--------------
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Vimc has a module parameter to configure the driver.
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* ``allocator=<unsigned int>``
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memory allocator selection, default is 0. It specifies the way buffers
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will be allocated.
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- 0: vmalloc
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- 1: dma-contig
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