| Laurent Pinchart | 176fb0d | 2009-12-09 08:39:58 -0300 | [diff] [blame^] | 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 | </chapter> |