diff options
Diffstat (limited to 'kernel/Documentation/DocBook/media/v4l/media-controller.xml')
| -rw-r--r-- | kernel/Documentation/DocBook/media/v4l/media-controller.xml | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/kernel/Documentation/DocBook/media/v4l/media-controller.xml b/kernel/Documentation/DocBook/media/v4l/media-controller.xml new file mode 100644 index 000000000..873ac3a62 --- /dev/null +++ b/kernel/Documentation/DocBook/media/v4l/media-controller.xml @@ -0,0 +1,89 @@ +<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> + + <section id="media-controller-model"> + <title>Media device model</title> + <para>Discovering a device internal topology, and configuring it at runtime, + is one of the goals of the media controller API. To achieve this, hardware + devices are modelled as an oriented graph of building blocks called entities + connected through pads.</para> + <para>An entity is a basic media hardware or software building block. It can + correspond to a large variety of logical blocks such as physical hardware + devices (CMOS sensor for instance), logical hardware devices (a building + block in a System-on-Chip image processing pipeline), DMA channels or + physical connectors.</para> + <para>A pad is a connection endpoint through which an entity can interact + with other entities. Data (not restricted to video) produced by an entity + flows from the entity's output to one or more entity inputs. Pads should not + be confused with physical pins at chip boundaries.</para> + <para>A link is a point-to-point oriented connection between two pads, + either on the same entity or on different entities. Data flows from a source + pad to a sink pad.</para> + </section> +</chapter> + +<appendix id="media-user-func"> + <title>Function Reference</title> + <!-- Keep this alphabetically sorted. --> + &sub-media-func-open; + &sub-media-func-close; + &sub-media-func-ioctl; + <!-- All ioctls go here. --> + &sub-media-ioc-device-info; + &sub-media-ioc-enum-entities; + &sub-media-ioc-enum-links; + &sub-media-ioc-setup-link; +</appendix> |