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The media_device structure abstracts functions common to all kind of media devices (v4l2, dvb, alsa, ...). It manages media entities and offers a userspace API to discover and configure the media device internal topology. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Acked-by: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
57 lines
2.3 KiB
XML
57 lines
2.3 KiB
XML
<partinfo>
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<authorgroup>
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<author>
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<firstname>Laurent</firstname>
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<surname>Pinchart</surname>
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<affiliation><address><email>laurent.pinchart@ideasonboard.com</email></address></affiliation>
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<contrib>Initial version.</contrib>
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</author>
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</authorgroup>
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<copyright>
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<year>2010</year>
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<holder>Laurent Pinchart</holder>
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</copyright>
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<revhistory>
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<!-- Put document revisions here, newest first. -->
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<revision>
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<revnumber>1.0.0</revnumber>
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<date>2010-11-10</date>
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<authorinitials>lp</authorinitials>
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<revremark>Initial revision</revremark>
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</revision>
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</revhistory>
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</partinfo>
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<title>Media Controller API</title>
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<chapter id="media_controller">
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<title>Media Controller</title>
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<section id="media-controller-intro">
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<title>Introduction</title>
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<para>Media devices increasingly handle multiple related functions. Many USB
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cameras include microphones, video capture hardware can also output video,
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or SoC camera interfaces also perform memory-to-memory operations similar to
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video codecs.</para>
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<para>Independent functions, even when implemented in the same hardware, can
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be modelled as separate devices. A USB camera with a microphone will be
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presented to userspace applications as V4L2 and ALSA capture devices. The
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devices' relationships (when using a webcam, end-users shouldn't have to
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manually select the associated USB microphone), while not made available
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directly to applications by the drivers, can usually be retrieved from
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sysfs.</para>
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<para>With more and more advanced SoC devices being introduced, the current
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approach will not scale. Device topologies are getting increasingly complex
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and can't always be represented by a tree structure. Hardware blocks are
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shared between different functions, creating dependencies between seemingly
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unrelated devices.</para>
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<para>Kernel abstraction APIs such as V4L2 and ALSA provide means for
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applications to access hardware parameters. As newer hardware expose an
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increasingly high number of those parameters, drivers need to guess what
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applications really require based on limited information, thereby
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implementing policies that belong to userspace.</para>
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<para>The media controller API aims at solving those problems.</para>
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</section>
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</chapter>
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