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4a2e0a806c
The vimc driver is used for testing purpose, and some test use cases involve sharing buffers with a consumer device. Consumers often require DMA contiguous memory, which vimc doesn't currently support. This leads in the best case to usage of bounce buffers, which is very slow, and in the worst case in a complete failure. Add support for the dma-contig allocator in vimc to support those use cases properly. The allocator is selected through a new "allocator" module parameter, which defaults to vmalloc. [hverkuil: add missing 'select VIDEOBUF2_DMA_CONFIG' to Kconfig] Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
92 lines
2.8 KiB
ReStructuredText
92 lines
2.8 KiB
ReStructuredText
.. 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 '"Sensor B":0[fmt:SBGGR8_1X8/640x480]'
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media-ctl -d platform:vimc -V '"Debayer B":0[fmt:SBGGR8_1X8/640x480]'
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v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=1920,height=1440
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v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v pixelformat=BA81
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v4l2-ctl -z platform:vimc -d "Raw Capture 1" -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-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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