Documentation/sound/alsa/soc/dapm.txt

   1 Dynamic Audio Power Management for Portable Devices
   2 ===================================================
   3
   4 1. Description
   5 ==============
   6
   7 Dynamic Audio Power Management (DAPM) is designed to allow portable Linux devices
   8 to use the minimum amount of power within the audio subsystem at all times. It
   9 is independent of other kernel PM and as such, can easily co-exist with the
  10 other PM systems.
  11
  12 DAPM is also completely transparent to all user space applications as all power
  13 switching is done within the ASoC core. No code changes or recompiling are
  14 required for user space applications. DAPM makes power switching decisions based
  15 upon any audio stream (capture/playback) activity and audio mixer settings
  16 within the device.
  17
  18 DAPM spans the whole machine. It covers power control within the entire audio
  19 subsystem, this includes internal codec power blocks and machine level power
  20 systems.
  21
  22 There are 4 power domains within DAPM
  23
  24    1. Codec domain - VREF, VMID (core codec and audio power)
  25       Usually controlled at codec probe/remove and suspend/resume, although
  26       can be set at stream time if power is not needed for sidetone, etc.
  27
  28    2. Platform/Machine domain - physically connected inputs and outputs
  29       Is platform/machine and user action specific, is configured by the
  30       machine driver and responds to asynchronous events e.g when HP
  31       are inserted
  32
  33    3. Path domain - audio susbsystem signal paths
  34       Automatically set when mixer and mux settings are changed by the user.
  35       e.g. alsamixer, amixer.
  36
  37    4. Stream domain - DAC's and ADC's.
  38       Enabled and disabled when stream playback/capture is started and
  39       stopped respectively. e.g. aplay, arecord.
  40
  41 All DAPM power switching decisions are made automatically by consulting an audio
  42 routing map of the whole machine. This map is specific to each machine and
  43 consists of the interconnections between every audio component (including
  44 internal codec components). All audio components that effect power are called
  45 widgets hereafter.
  46
  47
  48 2. DAPM Widgets
  49 ===============
  50
  51 Audio DAPM widgets fall into a number of types:-
  52
  53  o Mixer      - Mixes several analog signals into a single analog signal.
  54  o Mux        - An analog switch that outputs only 1 of it's inputs.
  55  o PGA        - A programmable gain amplifier or attenuation widget.
  56  o ADC        - Analog to Digital Converter
  57  o DAC        - Digital to Analog Converter
  58  o Switch     - An analog switch
  59  o Input      - A codec input pin
  60  o Output     - A codec output pin
  61  o Headphone  - Headphone (and optional Jack)
  62  o Mic        - Mic (and optional Jack)
  63  o Line       - Line Input/Output (and optional Jack)
  64  o Speaker    - Speaker
  65  o Pre        - Special PRE widget (exec before all others)
  66  o Post       - Special POST widget (exec after all others)
  67
  68 (Widgets are defined in include/sound/soc-dapm.h)
  69
  70 Widgets are usually added in the codec driver and the machine driver. There are
  71 convience macros defined in soc-dapm.h that can be used to quickly build a
  72 list of widgets of the codecs and machines DAPM widgets.
  73
  74 Most widgets have a name, register, shift and invert. Some widgets have extra
  75 parameters for stream name and kcontrols.
  76
  77
  78 2.1 Stream Domain Widgets
  79 -------------------------
  80
  81 Stream Widgets relate to the stream power domain and only consist of ADC's
  82 (analog to digital converters) and DAC's (digital to analog converters).
  83
  84 Stream widgets have the following format:-
  85
  86 SND_SOC_DAPM_DAC(name, stream name, reg, shift, invert),
  87
  88 NOTE: the stream name must match the corresponding stream name in your codecs
  89 snd_soc_codec_dai.
  90
  91 e.g. stream widgets for HiFi playback and capture
  92
  93 SND_SOC_DAPM_DAC("HiFi DAC", "HiFi Playback", REG, 3, 1),
  94 SND_SOC_DAPM_ADC("HiFi ADC", "HiFi Capture", REG, 2, 1),
  95
  96
  97 2.2 Path Domain Widgets
  98 -----------------------
  99
 100 Path domain widgets have a ability to control or effect the audio signal or
 101 audio paths within the audio subsystem. They have the following form:-
 102
 103 SND_SOC_DAPM_PGA(name, reg, shift, invert, controls, num_controls)
 104
 105 Any widget kcontrols can be set using the controls and num_controls members.
 106
 107 e.g. Mixer widget (the kcontrols are declared first)
 108
 109 /* Output Mixer */
 110 static const snd_kcontrol_new_t wm8731_output_mixer_controls[] = {
 111 SOC_DAPM_SINGLE("Line Bypass Switch", WM8731_APANA, 3, 1, 0),
 112 SOC_DAPM_SINGLE("Mic Sidetone Switch", WM8731_APANA, 5, 1, 0),
 113 SOC_DAPM_SINGLE("HiFi Playback Switch", WM8731_APANA, 4, 1, 0),
 114 };
 115
 116 SND_SOC_DAPM_MIXER("Output Mixer", WM8731_PWR, 4, 1, wm8731_output_mixer_controls,
 117         ARRAY_SIZE(wm8731_output_mixer_controls)),
 118
 119
 120 2.3 Platform/Machine domain Widgets
 121 -----------------------------------
 122
 123 Machine widgets are different from codec widgets in that they don't have a
 124 codec register bit associated with them. A machine widget is assigned to each
 125 machine audio component (non codec) that can be independently powered. e.g.
 126
 127  o Speaker Amp
 128  o Microphone Bias
 129  o Jack connectors
 130
 131 A machine widget can have an optional call back.
 132
 133 e.g. Jack connector widget for an external Mic that enables Mic Bias
 134 when the Mic is inserted:-
 135
 136 static int spitz_mic_bias(struct snd_soc_dapm_widget* w, int event)
 137 {
 138         if(SND_SOC_DAPM_EVENT_ON(event))
 139                 set_scoop_gpio(&spitzscoop2_device.dev, SPITZ_SCP2_MIC_BIAS);
 140         else
 141                 reset_scoop_gpio(&spitzscoop2_device.dev, SPITZ_SCP2_MIC_BIAS);
 142
 143         return 0;
 144 }
 145
 146 SND_SOC_DAPM_MIC("Mic Jack", spitz_mic_bias),
 147
 148
 149 2.4 Codec Domain
 150 ----------------
 151
 152 The Codec power domain has no widgets and is handled by the codecs DAPM event
 153 handler. This handler is called when the codec powerstate is changed wrt to any
 154 stream event or by kernel PM events.
 155
 156
 157 2.5 Virtual Widgets
 158 -------------------
 159
 160 Sometimes widgets exist in the codec or machine audio map that don't have any
 161 corresponding register bit for power control. In this case it's necessary to
 162 create a virtual widget - a widget with no control bits e.g.
 163
 164 SND_SOC_DAPM_MIXER("AC97 Mixer", SND_SOC_DAPM_NOPM, 0, 0, NULL, 0),
 165
 166 This can be used to merge to signal paths together in software.
 167
 168 After all the widgets have been defined, they can then be added to the DAPM
 169 subsystem individually with a call to snd_soc_dapm_new_control().
 170
 171
 172 3. Codec Widget Interconnections
 173 ================================
 174
 175 Widgets are connected to each other within the codec and machine by audio
 176 paths (called interconnections). Each interconnection must be defined in order
 177 to create a map of all audio paths between widgets.
 178 This is easiest with a diagram of the codec (and schematic of the machine audio
 179 system), as it requires joining widgets together via their audio signal paths.
 180
 181 i.e. from the WM8731 codec's output mixer (wm8731.c)
 182
 183 The WM8731 output mixer has 3 inputs (sources)
 184
 185  1. Line Bypass Input
 186  2. DAC (HiFi playback)
 187  3. Mic Sidetone Input
 188
 189 Each input in this example has a kcontrol associated with it (defined in example
 190 above) and is connected to the output mixer via it's kcontrol name. We can now
 191 connect the destination widget (wrt audio signal) with it's source widgets.
 192
 193         /* output mixer */
 194         {"Output Mixer", "Line Bypass Switch", "Line Input"},
 195         {"Output Mixer", "HiFi Playback Switch", "DAC"},
 196         {"Output Mixer", "Mic Sidetone Switch", "Mic Bias"},
 197
 198 So we have :-
 199
 200         Destination Widget  <=== Path Name <=== Source Widget
 201
 202 Or:-
 203
 204         Sink, Path, Source
 205
 206 Or :-
 207
 208         "Output Mixer" is connected to the "DAC" via the "HiFi Playback Switch".
 209
 210 When there is no path name connecting widgets (e.g. a direct connection) we
 211 pass NULL for the path name.
 212
 213 Interconnections are created with a call to:-
 214
 215 snd_soc_dapm_connect_input(codec, sink, path, source);
 216
 217 Finally, snd_soc_dapm_new_widgets(codec) must be called after all widgets and
 218 interconnections have been registered with the core. This causes the core to
 219 scan the codec and machine so that the internal DAPM state matches the
 220 physical state of the machine.
 221
 222
 223 3.1 Machine Widget Interconnections
 224 -----------------------------------
 225 Machine widget interconnections are created in the same way as codec ones and
 226 directly connect the codec pins to machine level widgets.
 227
 228 e.g. connects the speaker out codec pins to the internal speaker.
 229
 230         /* ext speaker connected to codec pins LOUT2, ROUT2  */
 231         {"Ext Spk", NULL , "ROUT2"},
 232         {"Ext Spk", NULL , "LOUT2"},
 233
 234 This allows the DAPM to power on and off pins that are connected (and in use)
 235 and pins that are NC respectively.
 236
 237
 238 4 Endpoint Widgets
 239 ===================
 240 An endpoint is a start or end point (widget) of an audio signal within the
 241 machine and includes the codec. e.g.
 242
 243  o Headphone Jack
 244  o Internal Speaker
 245  o Internal Mic
 246  o Mic Jack
 247  o Codec Pins
 248
 249 When a codec pin is NC it can be marked as not used with a call to
 250
 251 snd_soc_dapm_set_endpoint(codec, "Widget Name", 0);
 252
 253 The last argument is 0 for inactive and 1 for active. This way the pin and its
 254 input widget will never be powered up and consume power.
 255
 256 This also applies to machine widgets. e.g. if a headphone is connected to a
 257 jack then the jack can be marked active. If the headphone is removed, then
 258 the headphone jack can be marked inactive.
 259
 260
 261 5 DAPM Widget Events
 262 ====================
 263
 264 Some widgets can register their interest with the DAPM core in PM events.
 265 e.g. A Speaker with an amplifier registers a widget so the amplifier can be
 266 powered only when the spk is in use.
 267
 268 /* turn speaker amplifier on/off depending on use */
 269 static int corgi_amp_event(struct snd_soc_dapm_widget *w, int event)
 270 {
 271         if (SND_SOC_DAPM_EVENT_ON(event))
 272                 set_scoop_gpio(&corgiscoop_device.dev, CORGI_SCP_APM_ON);
 273         else
 274                 reset_scoop_gpio(&corgiscoop_device.dev, CORGI_SCP_APM_ON);
 275
 276         return 0;
 277 }
 278
 279 /* corgi machine dapm widgets */
 280 static const struct snd_soc_dapm_widget wm8731_dapm_widgets =
 281         SND_SOC_DAPM_SPK("Ext Spk", corgi_amp_event);
 282
 283 Please see soc-dapm.h for all other widgets that support events.
 284
 285
 286 5.1 Event types
 287 ---------------
 288
 289 The following event types are supported by event widgets.
 290
 291 /* dapm event types */
 292 #define SND_SOC_DAPM_PRE_PMU    0x1     /* before widget power up */
 293 #define SND_SOC_DAPM_POST_PMU   0x2             /* after widget power up */
 294 #define SND_SOC_DAPM_PRE_PMD    0x4     /* before widget power down */
 295 #define SND_SOC_DAPM_POST_PMD   0x8             /* after widget power down */
 296 #define SND_SOC_DAPM_PRE_REG    0x10    /* before audio path setup */
 297 #define SND_SOC_DAPM_POST_REG   0x20    /* after audio path setup */