sound/soc/overview.rst

6 provide better ALSA support for embedded system-on-chip processors (e.g.
7 pxa2xx, au1x00, iMX, etc) and portable audio codecs.  Prior to the ASoC
8 subsystem there was some support in the kernel for SoC audio, however it
9 had some limitations:-
12     CPU. This is not ideal and leads to code duplication - for example,
15   * There was no standard method to signal user initiated audio events (e.g.
18     machine specific code to re-route audio, enable amps, etc., after such an
22     recording) audio. This is fine for a PC, but tends to waste a lot of
31 features :-
36   * Easy I2S/PCM audio interface setup between codec and SoC. Each SoC
37     interface and codec registers its audio interface capabilities with the
41   * Dynamic Audio Power Management (DAPM). DAPM automatically sets the codec to
43     internal power blocks depending on the internal codec audio routing and any
50   * Machine specific controls: Allow machines to add controls to the sound card
53 To achieve all this, ASoC basically splits an embedded audio system into
54 multiple re-usable component drivers :-
57     contains audio controls, audio interface capabilities, codec DAPM
62   * Platform class drivers: The platform class driver includes the audio DMA
63     engine driver, digital audio interface (DAI) drivers (e.g. I2S, AC97, PCM)
64     and any audio DSP drivers for that platform.
68     "sound card device". It handles any machine specific controls and
69     machine level audio events (e.g. turning on an amp at start of playback).