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diff --git a/Documentation/userspace-api/media/mediactl/media-controller-intro.rst b/Documentation/userspace-api/media/mediactl/media-controller-intro.rst new file mode 100644 index 000000000000..1d06ea4c4d09 --- /dev/null +++ b/Documentation/userspace-api/media/mediactl/media-controller-intro.rst @@ -0,0 +1,40 @@ +.. Permission is granted to copy, distribute and/or modify this +.. document under the terms of the GNU Free Documentation License, +.. Version 1.1 or any later version published by the Free Software +.. Foundation, with no Invariant Sections, no Front-Cover Texts +.. and no Back-Cover Texts. A copy of the license is included at +.. Documentation/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +.. _media-controller-intro: + +Introduction +============ + +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. + +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. + +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. + +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. + +The media controller API aims at solving those problems. |