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>
90