发布时间：2023-06-27 19:00
Dynamic Audio Power Management for Portable Devices
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1. Description
==============
Dynamic Audio Power Management (DAPM) is designed to allow portable Linux devices to use the minimum amount of power within the audio subsystem at all times. It is independent of other kernel PM and as such, can easily co-exist with the other PM systems.
DAPM，音频电源动态管理，不依赖kernel其他电源管理，可以方便地和其他电源管理系统共同存在
DAPM is also completely transparent to all user space applications as all power switching is done within the ASoC core. No code changes or recompiling are required for user space applications. DAPM makes power switching decisions based upon any audio stream (capture/playback) activity and audio mixer settings within the device.
DAPM对用户空间的应用是透明的，所有电源转换都在ASoC核心部分完成。用户空间不需要修改代码或者重新编译代码。DAPM使得电源切换是基于设备的音频流（获取流和播放流）、行为和音频混音设置。
DAPM spans the whole machine. It covers power control within the entire audio subsystem, this includes internal codec power blocks and machine level power systems.
DAPM跨越整个平台，覆盖了全部音频子系统的电源控制，包括内部codec电源模块和平台级电源系统。
There are 4 power domains within DAPM
1. Codec domain - VREF, VMID (core codec and audio power) Usually controlled at codec probe/remove and suspend/resume, although can be set at stream time if power is not needed for sidetone, etc.
2. Platform/Machine domain - physically connected inputs and outputs Is platform/machine and user action specific, is configured by the machine driver and responds to asynchronous events e.g when HP are inserted
3. Path domain - audio susbsystem signal paths Automatically set when mixer and mux settings are changed by the user. e.g. alsamixer, amixer.
4. Stream domain - DACs and ADCs. Enabled and disabled when stream playback/capture is started and stopped respectively. e.g. aplay, arecord.
All DAPM power switching decisions are made automatically by consulting an audio routing map of the whole machine. This map is specific to each machine and consists of the interconnections between every audio component (including internal codec components). All audio components that effect power are called widgets hereafter.
所有的DAPM电源切换，都是通过遍历全部平台的音频路由表后自动决定的。每个平台的路由表都是特定明确的，由内部每个音频组件（包括内部codec组件）的连接组成。这里，所有影响电源的音频组件都称为微件（widget）。
2. DAPM Widgets
===============
Audio DAPM widgets fall into a number of types:-
o Mixer - Mixes several analog signals into a single analog signal.
o Mux - An analog switch that outputs only one of many inputs.
o PGA - A programmable gain amplifier or attenuation widget.
o ADC - Analog to Digital Converter
o DAC - Digital to Analog Converter
o Switch - An analog switch
o Input - A codec input pin
o Output - A codec output pin
o Headphone - Headphone (and optional Jack)
o Mic - Mic (and optional Jack)
o Line - Line Input/Output (and optional Jack)
o Speaker - Speaker
o Supply - Power or clock supply widget used by other widgets.
o Pre - Special PRE widget (exec before all others)
o Post - Special POST widget (exec after all others)
(Widgets are defined in include/sound/soc-dapm.h)
Widgets are usually added in the codec driver and the machine driver. There are convenience macros defined in soc-dapm.h that can be used to quickly build a list of widgets of the codecs and machines DAPM widgets.
微件一般是在codec驱动和平台驱动中添加，在soc-dapm.h中有方便的定义，可以用于很快地建立一条codec微件链和平台DAPM微件链。
Most widgets have a name, register, shift and invert. Some widgets have extra parameters for stream name and kcontrols.
多部分的微件有微件名称、寄存器、位偏移、位反相，部分微件会有其他的参数。
2.1 Stream Domain Widgets
-------------------------
Stream Widgets relate to the stream power domain and only consist of ADCs (analog to digital converters) and DACs (digital to analog converters).
Stream widgets have the following format:-
SND_SOC_DAPM_DAC(name, stream name, reg, shift, invert),
NOTE: the stream name must match the corresponding stream name in your codec snd_soc_codec_dai.
e.g. stream widgets for HiFi playback and capture
【Hi-Fi是High-Fidelity的缩写，“高保真”，定义：与原来的声音高度相似的重放声音】
SND_SOC_DAPM_DAC(\"HiFi DAC\", \"HiFi Playback\", REG, 3, 1), SND_SOC_DAPM_ADC(\"HiFi ADC\", \"HiFi Capture\", REG, 2, 1),
2.2 Path Domain Widgets
-----------------------
Path domain widgets have a ability to control or affect the audio signal or audio paths within the audio subsystem. They have the following form:-
SND_SOC_DAPM_PGA(name, reg, shift, invert, controls, num_controls)
Any widget kcontrols can be set using the controls and num_controls members.
e.g. Mixer widget (the kcontrols are declared first)
/* Output Mixer */ static const snd_kcontrol_new_t wm8731_output_mixer_controls[] = { SOC_DAPM_SINGLE(\"Line Bypass Switch\", WM8731_APANA, 3, 1, 0), SOC_DAPM_SINGLE(\"Mic Sidetone Switch\", WM8731_APANA, 5, 1, 0), SOC_DAPM_SINGLE(\"HiFi Playback Switch\", WM8731_APANA, 4, 1, 0), };
SND_SOC_DAPM_MIXER(\"Output Mixer\", WM8731_PWR, 4, 1,
wm8731_output_mixer_controls, ARRAY_SIZE(wm8731_output_mixer_controls)),
If you dont want the mixer elements prefixed with the name of the mixer widget, you can use SND_SOC_DAPM_MIXER_NAMED_CTL instead. the parameters are the same as for SND_SOC_DAPM_MIXER.
2.3 Platform/Machine domain Widgets
-----------------------------------
Machine widgets are different from codec widgets in that they don\'t have a codec register bit associated with them. A machine widget is assigned to each machine audio component (non codec) that can be independently powered.
平台微件区别于codec微件的是，它没有相关的codec寄存器，平台微件被分配到每一个平台音频组件中，单独驱动。
e.g.
o Speaker Amp
o Microphone Bias
o Jack connectors
A machine widget can have an optional call back.
平台微件可以有一个可选的回调
e.g. Jack connector widget for an external Mic that enables Mic Bias when the Mic is inserted:-
static int spitz_mic_bias(struct snd_soc_dapm_widget* w, int event) { gpio_set_value(SPITZ_GPIO_MIC_BIAS, SND_SOC_DAPM_EVENT_ON(event)); return 0; }
SND_SOC_DAPM_MIC(\"Mic Jack\", spitz_mic_bias),
2.4 Codec Domain
----------------
The codec power domain has no widgets and is handled by the codecs DAPM event handler. This handler is called when the codec powerstate is changed wrt to any stream event or by kernel PM events.
Codec电源域没有微件，而是通过codecDAPM时间的把柄来控制。这个把柄在codec电压供电状态被改变或者kernel其他电源管理事件发生时候被调用。
2.5 Virtual Widgets
-------------------
Sometimes widgets exist in the codec or machine audio map that don\'t have any corresponding soft power control. In this case it is necessary to create a virtual widget - a widget with no control bits e.g.
SND_SOC_DAPM_MIXER(\"AC97 Mixer\", SND_SOC_DAPM_NOPM, 0, 0, NULL, 0),
This can be used to merge to signal paths together in software.
虚拟微件可以用于软件合并信号路径
After all the widgets have been defined, they can then be added to the DAPM subsystem individually with a call to snd_soc_dapm_new_control().
定义完所有的微件，分别调用snd_soc_dapm_new_control()将微件添加到DAPM子系统中。
3. Codec Widget Interconnections
================================
Widgets are connected to each other within the codec and machine by audio paths (called interconnections). Each interconnection must be defined in order to create a map of all audio paths between widgets.
codec和平台之间的微件是通过路径连接的，也叫做内部连接。每一个内联必须是定义过的，以便于在微件间建立一张音频通路路径图。
This is easiest with a diagram of the codec (and schematic of the machine audio system), as it requires joining widgets together via their audio signal paths.
这个可以通过codec的图表（和平台的音频系统原理图）轻松实现，因为它们也需要通过音频信号路径把所有的微件连接起来。
e.g., from the WM8731 output mixer (wm8731.c)
The WM8731 output mixer has 3 inputs (sources)
1. Line Bypass Input
2. DAC (HiFi playback)
3. Mic Sidetone Input
Each input in this example has a kcontrol associated with it (defined in example above) and is connected to the output mixer via it\'s kcontrol name. We can now connect the destination widget (wrt audio signal) with it\'s source widgets.
/* output mixer */
{\"Output Mixer\", \"Line Bypass Switch\", \"Line Input\"},
{\"Output Mixer\", \"HiFi Playback Switch\", \"DAC\"},
{\"Output Mixer\", \"Mic Sidetone Switch\", \"Mic Bias\"},
So we have :-
Destination Widget <=== Path Name <=== Source Widget
Or:-
Sink, Path, Source
Or :-
\"Output Mixer\" is connected to the \"DAC\" via the \"HiFi Playback Switch\".
When there is no path name connecting widgets (e.g. a direct connection) we pass NULL for the path name.
Interconnections are created with a call to:-
snd_soc_dapm_connect_input(codec, sink, path, source);
Finally, snd_soc_dapm_new_widgets(codec) must be called after all widgets and interconnections have been registered with the core. This causes the core to scan the codec and machine so that the internal DAPM state matches the physical state of the machine.
最后，在所有的微件和内联都注册到core里面之后，需要调用到函数snd_soc_dapm_new_widgets(codec)。 这样core会扫描codec和machine以便于内部DAPM的状态与machine物理状态保持一致。
3.1 Machine Widget Interconnections
-----------------------------------
Machine widget interconnections are created in the same way as codec ones and directly connect the codec pins to machine level widgets.
e.g. connects the speaker out codec pins to the internal speaker.
/* ext speaker connected to codec pins LOUT2, ROUT2 */
{\"Ext Spk\", NULL , \"ROUT2\"},
{\"Ext Spk\", NULL , \"LOUT2\"},
This allows the DAPM to power on and off pins that are connected (and in use) and pins that are NC respectively.
4、Endpoint Widgets
===================
An endpoint is a start or end point (widget) of an audio signal within the machine and includes the codec. e.g.
o Headphone Jack
o Internal Speaker
o Internal Mic
o Mic Jack
o Codec Pins
When a codec pin is NC it can be marked as not used with a call to
snd_soc_dapm_set_endpoint(codec, \"Widget Name\", 0);
The last argument is 0 for inactive and 1 for active. This way the pin and its input widget will never be powered up and consume power.
This also applies to machine widgets. e.g. if a headphone is connected to a jack then the jack can be marked active. If the headphone is removed, then the headphone jack can be marked inactive.
5、DAPM Widget Events
====================
Some widgets can register their interest with the DAPM core in PM events. e.g. A Speaker with an amplifier registers a widget so the amplifier can be powered only when the spk is in use.
/* turn speaker amplifier on/off depending on use */
static int corgi_amp_event(struct snd_soc_dapm_widget *w, int event)
{
gpio_set_value(CORGI_GPIO_APM_ON, SND_SOC_DAPM_EVENT_ON(event));
return 0;
}
/* corgi machine dapm widgets */ static const struct snd_soc_dapm_widget wm8731_dapm_widgets = SND_SOC_DAPM_SPK(\"Ext Spk\", corgi_amp_event);
Please see soc-dapm.h for all other widgets that support events.
5.1 Event types
---------------
The following event types are supported by event widgets.
/* dapm event types */ #define SND_SOC_DAPM_PRE_PMU 0x1 /* before widget power up */ #define SND_SOC_DAPM_POST_PMU 0x2 /* after widget power up */ #define SND_SOC_DAPM_PRE_PMD 0x4 /* before widget power down */ #define SND_SOC_DAPM_POST_PMD 0x8 /* after widget power down */ #define SND_SOC_DAPM_PRE_REG 0x10 /* before audio path setup */ #define SND_SOC_DAPM_POST_REG 0x20 /* after audio path setup */