299 lines
10 KiB
Plaintext
299 lines
10 KiB
Plaintext
Dynamic Audio Power Management for Portable Devices
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===================================================
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1. 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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1. Codec domain - 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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2. Platform/Machine domain - 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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3. Path domain - audio susbsystem 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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4. Stream domain - 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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2. DAPM Widgets
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===============
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Audio DAPM widgets fall into a number of types:-
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o Mixer - Mixes several analog signals into a single analog signal.
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o Mux - An analog switch that outputs only one of many inputs.
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o PGA - A programmable gain amplifier or attenuation widget.
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o ADC - Analog to Digital Converter
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o DAC - Digital to Analog Converter
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o Switch - An analog switch
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o Input - A codec input pin
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o Output - A codec output pin
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o Headphone - Headphone (and optional Jack)
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o Mic - Mic (and optional Jack)
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o Line - Line Input/Output (and optional Jack)
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o Speaker - Speaker
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o Pre - Special PRE widget (exec before all others)
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o Post - 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 are usually added in the codec driver and the machine driver. There are
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convience macros defined in soc-dapm.h that can be used to quickly build a
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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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2.1 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) and DACs (digital to analog converters).
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Stream widgets have the following format:-
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SND_SOC_DAPM_DAC(name, stream name, 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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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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2.2 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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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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/* 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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2.3 Platform/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) that can be independently powered. e.g.
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o Speaker Amp
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o Microphone Bias
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o 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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if(SND_SOC_DAPM_EVENT_ON(event))
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set_scoop_gpio(&spitzscoop2_device.dev, SPITZ_SCP2_MIC_BIAS);
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else
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reset_scoop_gpio(&spitzscoop2_device.dev, SPITZ_SCP2_MIC_BIAS);
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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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2.4 Codec Domain
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----------------
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The codec power domain has no widgets and is handled by the codecs DAPM event
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handler. This handler is called when the codec powerstate is changed wrt to any
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stream event or by kernel PM events.
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2.5 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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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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3. Codec Widget Interconnections
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================================
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Widgets are connected to each other within the codec and machine by audio paths
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(called interconnections). Each interconnection must be defined in order to
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create a map of all audio paths between widgets.
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This is easiest with a diagram of the codec (and schematic of the machine audio
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system), as it requires joining widgets together via their audio signal 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 it's kcontrol name. We can now
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connect the destination widget (wrt audio signal) with it's source widgets.
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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
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Or:-
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Sink, Path, Source
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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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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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3.1 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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/* 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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4 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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o Headphone Jack
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o Internal Speaker
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o Internal Mic
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o Mic Jack
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o Codec Pins
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When a codec pin is NC it can be marked as not used with a call to
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snd_soc_dapm_set_endpoint(codec, "Widget Name", 0);
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The last argument is 0 for inactive and 1 for active. This way the pin and its
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input widget will never be powered up and consume power.
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This also applies to machine widgets. e.g. if a headphone is connected to a
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jack then the jack can be marked active. If the headphone is removed, then
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the headphone jack can be marked inactive.
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5 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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/* 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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if (SND_SOC_DAPM_EVENT_ON(event))
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set_scoop_gpio(&corgiscoop_device.dev, CORGI_SCP_APM_ON);
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else
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reset_scoop_gpio(&corgiscoop_device.dev, CORGI_SCP_APM_ON);
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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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5.1 Event types
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---------------
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The following event types are supported by event widgets.
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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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