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Create the following ioctl and implement it at the media device level to setup links. - MEDIA_IOC_SETUP_LINK: Modify the properties of a given link The only property that can currently be modified is the ENABLED link flag to enable/disable a link. Links marked with the IMMUTABLE link flag can not be enabled or disabled. Enabling or disabling a link has effects on entities' use count. Those changes are automatically propagated through the graph. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Stanimir Varbanov <svarbanov@mm-sol.com> Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi> Acked-by: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
90 lines
3.8 KiB
XML
90 lines
3.8 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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<section id="media-controller-model">
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<title>Media device model</title>
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<para>Discovering a device internal topology, and configuring it at runtime,
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is one of the goals of the media controller API. To achieve this, hardware
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devices are modelled as an oriented graph of building blocks called entities
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connected through pads.</para>
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<para>An entity is a basic media hardware or software building block. It can
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correspond to a large variety of logical blocks such as physical hardware
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devices (CMOS sensor for instance), logical hardware devices (a building
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block in a System-on-Chip image processing pipeline), DMA channels or
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physical connectors.</para>
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<para>A pad is a connection endpoint through which an entity can interact
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with other entities. Data (not restricted to video) produced by an entity
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flows from the entity's output to one or more entity inputs. Pads should not
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be confused with physical pins at chip boundaries.</para>
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<para>A link is a point-to-point oriented connection between two pads,
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either on the same entity or on different entities. Data flows from a source
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pad to a sink pad.</para>
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</section>
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</chapter>
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<appendix id="media-user-func">
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<title>Function Reference</title>
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<!-- Keep this alphabetically sorted. -->
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&sub-media-open;
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&sub-media-close;
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&sub-media-ioctl;
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<!-- All ioctls go here. -->
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&sub-media-ioc-device-info;
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&sub-media-ioc-enum-entities;
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&sub-media-ioc-enum-links;
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&sub-media-ioc-setup-link;
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</appendix>
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