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