343 lines
10 KiB
ReStructuredText
343 lines
10 KiB
ReStructuredText
===================================================
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Dynamic Audio Power Management for Portable Devices
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===================================================
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Description
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===========
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Dynamic Audio Power Management (DAPM) is designed to allow portable
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Linux devices to use the minimum amount of power within the audio
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subsystem at all times. It is independent of other kernel PM and as
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such, can easily co-exist with the other PM systems.
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DAPM is also completely transparent to all user space applications as
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all power switching is done within the ASoC core. No code changes or
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recompiling are required for user space applications. DAPM makes power
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switching decisions based upon any audio stream (capture/playback)
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activity and audio mixer settings within the device.
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DAPM spans the whole machine. It covers power control within the entire
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audio subsystem, this includes internal codec power blocks and machine
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level power systems.
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There are 4 power domains within DAPM
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Codec bias domain
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VREF, VMID (core codec and audio power)
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Usually controlled at codec probe/remove and suspend/resume, although
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can be set at stream time if power is not needed for sidetone, etc.
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Platform/Machine domain
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physically connected inputs and outputs
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Is platform/machine and user action specific, is configured by the
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machine driver and responds to asynchronous events e.g when HP
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are inserted
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Path domain
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audio subsystem signal paths
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Automatically set when mixer and mux settings are changed by the user.
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e.g. alsamixer, amixer.
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Stream domain
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DACs and ADCs.
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Enabled and disabled when stream playback/capture is started and
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stopped respectively. e.g. aplay, arecord.
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All DAPM power switching decisions are made automatically by consulting an audio
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routing map of the whole machine. This map is specific to each machine and
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consists of the interconnections between every audio component (including
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internal codec components). All audio components that effect power are called
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widgets hereafter.
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DAPM Widgets
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============
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Audio DAPM widgets fall into a number of types:-
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Mixer
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Mixes several analog signals into a single analog signal.
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Mux
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An analog switch that outputs only one of many inputs.
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PGA
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A programmable gain amplifier or attenuation widget.
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ADC
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Analog to Digital Converter
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DAC
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Digital to Analog Converter
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Switch
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An analog switch
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Input
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A codec input pin
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Output
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A codec output pin
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Headphone
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Headphone (and optional Jack)
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Mic
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Mic (and optional Jack)
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Line
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Line Input/Output (and optional Jack)
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Speaker
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Speaker
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Supply
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Power or clock supply widget used by other widgets.
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Regulator
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External regulator that supplies power to audio components.
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Clock
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External clock that supplies clock to audio components.
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AIF IN
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Audio Interface Input (with TDM slot mask).
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AIF OUT
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Audio Interface Output (with TDM slot mask).
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Siggen
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Signal Generator.
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DAI IN
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Digital Audio Interface Input.
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DAI OUT
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Digital Audio Interface Output.
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DAI Link
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DAI Link between two DAI structures
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Pre
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Special PRE widget (exec before all others)
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Post
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Special POST widget (exec after all others)
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(Widgets are defined in include/sound/soc-dapm.h)
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Widgets can be added to the sound card by any of the component driver types.
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There are convenience macros defined in soc-dapm.h that can be used to quickly
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build a list of widgets of the codecs and machines DAPM widgets.
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Most widgets have a name, register, shift and invert. Some widgets have extra
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parameters for stream name and kcontrols.
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Stream Domain Widgets
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---------------------
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Stream Widgets relate to the stream power domain and only consist of ADCs
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(analog to digital converters), DACs (digital to analog converters),
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AIF IN and AIF OUT.
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Stream widgets have the following format:-
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::
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SND_SOC_DAPM_DAC(name, stream name, reg, shift, invert),
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SND_SOC_DAPM_AIF_IN(name, stream, slot, reg, shift, invert)
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NOTE: the stream name must match the corresponding stream name in your codec
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snd_soc_codec_dai.
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e.g. stream widgets for HiFi playback and capture
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::
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SND_SOC_DAPM_DAC("HiFi DAC", "HiFi Playback", REG, 3, 1),
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SND_SOC_DAPM_ADC("HiFi ADC", "HiFi Capture", REG, 2, 1),
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e.g. stream widgets for AIF
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::
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SND_SOC_DAPM_AIF_IN("AIF1RX", "AIF1 Playback", 0, SND_SOC_NOPM, 0, 0),
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SND_SOC_DAPM_AIF_OUT("AIF1TX", "AIF1 Capture", 0, SND_SOC_NOPM, 0, 0),
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Path Domain Widgets
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-------------------
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Path domain widgets have a ability to control or affect the audio signal or
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audio paths within the audio subsystem. They have the following form:-
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::
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SND_SOC_DAPM_PGA(name, reg, shift, invert, controls, num_controls)
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Any widget kcontrols can be set using the controls and num_controls members.
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e.g. Mixer widget (the kcontrols are declared first)
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::
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/* Output Mixer */
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static const snd_kcontrol_new_t wm8731_output_mixer_controls[] = {
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SOC_DAPM_SINGLE("Line Bypass Switch", WM8731_APANA, 3, 1, 0),
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SOC_DAPM_SINGLE("Mic Sidetone Switch", WM8731_APANA, 5, 1, 0),
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SOC_DAPM_SINGLE("HiFi Playback Switch", WM8731_APANA, 4, 1, 0),
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};
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SND_SOC_DAPM_MIXER("Output Mixer", WM8731_PWR, 4, 1, wm8731_output_mixer_controls,
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ARRAY_SIZE(wm8731_output_mixer_controls)),
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If you don't want the mixer elements prefixed with the name of the mixer widget,
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you can use SND_SOC_DAPM_MIXER_NAMED_CTL instead. the parameters are the same
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as for SND_SOC_DAPM_MIXER.
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Machine domain Widgets
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----------------------
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Machine widgets are different from codec widgets in that they don't have a
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codec register bit associated with them. A machine widget is assigned to each
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machine audio component (non codec or DSP) that can be independently
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powered. e.g.
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* Speaker Amp
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* Microphone Bias
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* Jack connectors
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A machine widget can have an optional call back.
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e.g. Jack connector widget for an external Mic that enables Mic Bias
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when the Mic is inserted:-::
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static int spitz_mic_bias(struct snd_soc_dapm_widget* w, int event)
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{
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gpio_set_value(SPITZ_GPIO_MIC_BIAS, SND_SOC_DAPM_EVENT_ON(event));
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return 0;
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}
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SND_SOC_DAPM_MIC("Mic Jack", spitz_mic_bias),
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Codec (BIAS) Domain
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-------------------
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The codec bias power domain has no widgets and is handled by the codecs DAPM
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event handler. This handler is called when the codec powerstate is changed wrt
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to any stream event or by kernel PM events.
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Virtual Widgets
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---------------
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Sometimes widgets exist in the codec or machine audio map that don't have any
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corresponding soft power control. In this case it is necessary to create
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a virtual widget - a widget with no control bits e.g.
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::
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SND_SOC_DAPM_MIXER("AC97 Mixer", SND_SOC_DAPM_NOPM, 0, 0, NULL, 0),
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This can be used to merge to signal paths together in software.
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After all the widgets have been defined, they can then be added to the DAPM
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subsystem individually with a call to snd_soc_dapm_new_control().
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Codec/DSP Widget Interconnections
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=================================
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Widgets are connected to each other within the codec, platform and machine by
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audio paths (called interconnections). Each interconnection must be defined in
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order to create a map of all audio paths between widgets.
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This is easiest with a diagram of the codec or DSP (and schematic of the machine
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audio system), as it requires joining widgets together via their audio signal
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paths.
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e.g., from the WM8731 output mixer (wm8731.c)
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The WM8731 output mixer has 3 inputs (sources)
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1. Line Bypass Input
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2. DAC (HiFi playback)
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3. Mic Sidetone Input
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Each input in this example has a kcontrol associated with it (defined in example
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above) and is connected to the output mixer via its kcontrol name. We can now
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connect the destination widget (wrt audio signal) with its source widgets.
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::
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/* output mixer */
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{"Output Mixer", "Line Bypass Switch", "Line Input"},
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{"Output Mixer", "HiFi Playback Switch", "DAC"},
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{"Output Mixer", "Mic Sidetone Switch", "Mic Bias"},
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So we have :-
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* Destination Widget <=== Path Name <=== Source Widget, or
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* Sink, Path, Source, or
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* ``Output Mixer`` is connected to the ``DAC`` via the ``HiFi Playback Switch``.
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When there is no path name connecting widgets (e.g. a direct connection) we
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pass NULL for the path name.
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Interconnections are created with a call to:-
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::
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snd_soc_dapm_connect_input(codec, sink, path, source);
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Finally, snd_soc_dapm_new_widgets(codec) must be called after all widgets and
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interconnections have been registered with the core. This causes the core to
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scan the codec and machine so that the internal DAPM state matches the
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physical state of the machine.
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Machine Widget Interconnections
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-------------------------------
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Machine widget interconnections are created in the same way as codec ones and
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directly connect the codec pins to machine level widgets.
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e.g. connects the speaker out codec pins to the internal speaker.
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::
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/* ext speaker connected to codec pins LOUT2, ROUT2 */
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{"Ext Spk", NULL , "ROUT2"},
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{"Ext Spk", NULL , "LOUT2"},
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This allows the DAPM to power on and off pins that are connected (and in use)
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and pins that are NC respectively.
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Endpoint Widgets
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================
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An endpoint is a start or end point (widget) of an audio signal within the
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machine and includes the codec. e.g.
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* Headphone Jack
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* Internal Speaker
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* Internal Mic
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* Mic Jack
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* Codec Pins
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Endpoints are added to the DAPM graph so that their usage can be determined in
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order to save power. e.g. NC codecs pins will be switched OFF, unconnected
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jacks can also be switched OFF.
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DAPM Widget Events
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==================
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Some widgets can register their interest with the DAPM core in PM events.
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e.g. A Speaker with an amplifier registers a widget so the amplifier can be
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powered only when the spk is in use.
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::
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/* turn speaker amplifier on/off depending on use */
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static int corgi_amp_event(struct snd_soc_dapm_widget *w, int event)
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{
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gpio_set_value(CORGI_GPIO_APM_ON, SND_SOC_DAPM_EVENT_ON(event));
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return 0;
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}
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/* corgi machine dapm widgets */
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static const struct snd_soc_dapm_widget wm8731_dapm_widgets =
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SND_SOC_DAPM_SPK("Ext Spk", corgi_amp_event);
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Please see soc-dapm.h for all other widgets that support events.
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Event types
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-----------
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The following event types are supported by event widgets.
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::
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/* dapm event types */
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#define SND_SOC_DAPM_PRE_PMU 0x1 /* before widget power up */
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#define SND_SOC_DAPM_POST_PMU 0x2 /* after widget power up */
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#define SND_SOC_DAPM_PRE_PMD 0x4 /* before widget power down */
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#define SND_SOC_DAPM_POST_PMD 0x8 /* after widget power down */
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#define SND_SOC_DAPM_PRE_REG 0x10 /* before audio path setup */
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#define SND_SOC_DAPM_POST_REG 0x20 /* after audio path setup */
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