[media] media: Media device

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>

1 files changed, 56 insertions, 0 deletions

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