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Based on kernel version 3.16. Page generated on 2014-08-06 21:38 EST.

1	<partinfo>
2	  <authorgroup>
3	    <author>
4	      <firstname>Laurent</firstname>
5	      <surname>Pinchart</surname>
6	      <affiliation><address><email>laurent.pinchart@ideasonboard.com</email></address></affiliation>
7	      <contrib>Initial version.</contrib>
8	    </author>
9	  </authorgroup>
10	  <copyright>
11	    <year>2010</year>
12	    <holder>Laurent Pinchart</holder>
13	  </copyright>
14	
15	  <revhistory>
16	    <!-- Put document revisions here, newest first. -->
17	    <revision>
18	      <revnumber>1.0.0</revnumber>
19	      <date>2010-11-10</date>
20	      <authorinitials>lp</authorinitials>
21	      <revremark>Initial revision</revremark>
22	    </revision>
23	  </revhistory>
24	</partinfo>
25	
26	<title>Media Controller API</title>
27	
28	<chapter id="media_controller">
29	  <title>Media Controller</title>
30	
31	  <section id="media-controller-intro">
32	    <title>Introduction</title>
33	    <para>Media devices increasingly handle multiple related functions. Many USB
34	    cameras include microphones, video capture hardware can also output video,
35	    or SoC camera interfaces also perform memory-to-memory operations similar to
36	    video codecs.</para>
37	    <para>Independent functions, even when implemented in the same hardware, can
38	    be modelled as separate devices. A USB camera with a microphone will be
39	    presented to userspace applications as V4L2 and ALSA capture devices. The
40	    devices' relationships (when using a webcam, end-users shouldn't have to
41	    manually select the associated USB microphone), while not made available
42	    directly to applications by the drivers, can usually be retrieved from
43	    sysfs.</para>
44	    <para>With more and more advanced SoC devices being introduced, the current
45	    approach will not scale. Device topologies are getting increasingly complex
46	    and can't always be represented by a tree structure. Hardware blocks are
47	    shared between different functions, creating dependencies between seemingly
48	    unrelated devices.</para>
49	    <para>Kernel abstraction APIs such as V4L2 and ALSA provide means for
50	    applications to access hardware parameters. As newer hardware expose an
51	    increasingly high number of those parameters, drivers need to guess what
52	    applications really require based on limited information, thereby
53	    implementing policies that belong to userspace.</para>
54	    <para>The media controller API aims at solving those problems.</para>
55	  </section>
56	
57	  <section id="media-controller-model">
58	    <title>Media device model</title>
59	    <para>Discovering a device internal topology, and configuring it at runtime,
60	    is one of the goals of the media controller API. To achieve this, hardware
61	    devices are modelled as an oriented graph of building blocks called entities
62	    connected through pads.</para>
63	    <para>An entity is a basic media hardware or software building block. It can
64	    correspond to a large variety of logical blocks such as physical hardware
65	    devices (CMOS sensor for instance), logical hardware devices (a building
66	    block in a System-on-Chip image processing pipeline), DMA channels or
67	    physical connectors.</para>
68	    <para>A pad is a connection endpoint through which an entity can interact
69	    with other entities. Data (not restricted to video) produced by an entity
70	    flows from the entity's output to one or more entity inputs. Pads should not
71	    be confused with physical pins at chip boundaries.</para>
72	    <para>A link is a point-to-point oriented connection between two pads,
73	    either on the same entity or on different entities. Data flows from a source
74	    pad to a sink pad.</para>
75	  </section>
76	</chapter>
77	
78	<appendix id="media-user-func">
79	  <title>Function Reference</title>
80	  <!-- Keep this alphabetically sorted. -->
81	  &sub-media-func-open;
82	  &sub-media-func-close;
83	  &sub-media-func-ioctl;
84	  <!-- All ioctls go here. -->
85	  &sub-media-ioc-device-info;
86	  &sub-media-ioc-enum-entities;
87	  &sub-media-ioc-enum-links;
88	  &sub-media-ioc-setup-link;
89	</appendix>
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