Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  1) =======================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  2) ALSA SoC Layer Overview
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  3) =======================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  4) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  5) The overall project goal of the ALSA System on Chip (ASoC) layer is to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  6) provide better ALSA support for embedded system-on-chip processors (e.g.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  7) pxa2xx, au1x00, iMX, etc) and portable audio codecs.  Prior to the ASoC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  8) subsystem there was some support in the kernel for SoC audio, however it
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  9) had some limitations:-
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11)   * Codec drivers were often tightly coupled to the underlying SoC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12)     CPU. This is not ideal and leads to code duplication - for example,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13)     Linux had different wm8731 drivers for 4 different SoC platforms.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15)   * There was no standard method to signal user initiated audio events (e.g.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16)     Headphone/Mic insertion, Headphone/Mic detection after an insertion
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17)     event). These are quite common events on portable devices and often require
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18)     machine specific code to re-route audio, enable amps, etc., after such an
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19)     event.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21)   * Drivers tended to power up the entire codec when playing (or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22)     recording) audio. This is fine for a PC, but tends to waste a lot of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23)     power on portable devices. There was also no support for saving
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24)     power via changing codec oversampling rates, bias currents, etc.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) ASoC Design
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) ===========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) The ASoC layer is designed to address these issues and provide the following
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) features :-
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33)   * Codec independence. Allows reuse of codec drivers on other platforms
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34)     and machines.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36)   * Easy I2S/PCM audio interface setup between codec and SoC. Each SoC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37)     interface and codec registers its audio interface capabilities with the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38)     core and are subsequently matched and configured when the application
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39)     hardware parameters are known.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41)   * Dynamic Audio Power Management (DAPM). DAPM automatically sets the codec to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42)     its minimum power state at all times. This includes powering up/down
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43)     internal power blocks depending on the internal codec audio routing and any
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44)     active streams.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46)   * Pop and click reduction. Pops and clicks can be reduced by powering the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47)     codec up/down in the correct sequence (including using digital mute). ASoC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48)     signals the codec when to change power states.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50)   * Machine specific controls: Allow machines to add controls to the sound card
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51)     (e.g. volume control for speaker amplifier).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) To achieve all this, ASoC basically splits an embedded audio system into
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) multiple re-usable component drivers :-
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56)   * Codec class drivers: The codec class driver is platform independent and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57)     contains audio controls, audio interface capabilities, codec DAPM
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58)     definition and codec IO functions. This class extends to BT, FM and MODEM
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59)     ICs if required. Codec class drivers should be generic code that can run
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60)     on any architecture and machine.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62)   * Platform class drivers: The platform class driver includes the audio DMA
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63)     engine driver, digital audio interface (DAI) drivers (e.g. I2S, AC97, PCM)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64)     and any audio DSP drivers for that platform.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66)   * Machine class driver: The machine driver class acts as the glue that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67)     describes and binds the other component drivers together to form an ALSA
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68)     "sound card device". It handles any machine specific controls and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69)     machine level audio events (e.g. turning on an amp at start of playback).