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- .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
- .. _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.
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