Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  1) .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  2) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  3) .. _media-controller-intro:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  4) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  5) Introduction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  6) ============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  7) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  8) Media devices increasingly handle multiple related functions. Many USB
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  9) cameras include microphones, video capture hardware can also output
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) video, or SoC camera interfaces also perform memory-to-memory operations
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) similar to video codecs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) Independent functions, even when implemented in the same hardware, can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) be modelled as separate devices. A USB camera with a microphone will be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) presented to userspace applications as V4L2 and ALSA capture devices.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) The devices' relationships (when using a webcam, end-users shouldn't
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) have to manually select the associated USB microphone), while not made
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) available directly to applications by the drivers, can usually be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) retrieved from sysfs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) With more and more advanced SoC devices being introduced, the current
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) approach will not scale. Device topologies are getting increasingly
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) complex and can't always be represented by a tree structure. Hardware
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) blocks are shared between different functions, creating dependencies
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) between seemingly unrelated devices.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) Kernel abstraction APIs such as V4L2 and ALSA provide means for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) applications to access hardware parameters. As newer hardware expose an
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) increasingly high number of those parameters, drivers need to guess what
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) applications really require based on limited information, thereby
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) implementing policies that belong to userspace.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) The media controller API aims at solving those problems.