Based on kernel version 4.9. Page generated on 2016-12-21 14:37 EST.
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 8 Linux devices to use the minimum amount of power within the audio 9 subsystem at all times. It is independent of other kernel PM and as 10 such, can easily co-exist with the other PM systems. 11 12 DAPM is also completely transparent to all user space applications as 13 all power switching is done within the ASoC core. No code changes or 14 recompiling are required for user space applications. DAPM makes power 15 switching decisions based upon any audio stream (capture/playback) 16 activity and audio mixer settings within the device. 17 18 DAPM spans the whole machine. It covers power control within the entire 19 audio subsystem, this includes internal codec power blocks and machine 20 level power systems. 21 22 There are 4 power domains within DAPM 23 24 1. Codec bias 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 subsystem 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 - DACs and ADCs. 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 one of many 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 Supply - Power or clock supply widget used by other widgets. 66 o Regulator - External regulator that supplies power to audio components. 67 o Clock - External clock that supplies clock to audio components. 68 o AIF IN - Audio Interface Input (with TDM slot mask). 69 o AIF OUT - Audio Interface Output (with TDM slot mask). 70 o Siggen - Signal Generator. 71 o DAI IN - Digital Audio Interface Input. 72 o DAI OUT - Digital Audio Interface Output. 73 o DAI Link - DAI Link between two DAI structures */ 74 o Pre - Special PRE widget (exec before all others) 75 o Post - Special POST widget (exec after all others) 76 77 (Widgets are defined in include/sound/soc-dapm.h) 78 79 Widgets can be added to the sound card by any of the component driver types. 80 There are convenience macros defined in soc-dapm.h that can be used to quickly 81 build a list of widgets of the codecs and machines DAPM widgets. 82 83 Most widgets have a name, register, shift and invert. Some widgets have extra 84 parameters for stream name and kcontrols. 85 86 87 2.1 Stream Domain Widgets 88 ------------------------- 89 90 Stream Widgets relate to the stream power domain and only consist of ADCs 91 (analog to digital converters), DACs (digital to analog converters), 92 AIF IN and AIF OUT. 93 94 Stream widgets have the following format:- 95 96 SND_SOC_DAPM_DAC(name, stream name, reg, shift, invert), 97 SND_SOC_DAPM_AIF_IN(name, stream, slot, reg, shift, invert) 98 99 NOTE: the stream name must match the corresponding stream name in your codec 100 snd_soc_codec_dai. 101 102 e.g. stream widgets for HiFi playback and capture 103 104 SND_SOC_DAPM_DAC("HiFi DAC", "HiFi Playback", REG, 3, 1), 105 SND_SOC_DAPM_ADC("HiFi ADC", "HiFi Capture", REG, 2, 1), 106 107 e.g. stream widgets for AIF 108 109 SND_SOC_DAPM_AIF_IN("AIF1RX", "AIF1 Playback", 0, SND_SOC_NOPM, 0, 0), 110 SND_SOC_DAPM_AIF_OUT("AIF1TX", "AIF1 Capture", 0, SND_SOC_NOPM, 0, 0), 111 112 113 2.2 Path Domain Widgets 114 ----------------------- 115 116 Path domain widgets have a ability to control or affect the audio signal or 117 audio paths within the audio subsystem. They have the following form:- 118 119 SND_SOC_DAPM_PGA(name, reg, shift, invert, controls, num_controls) 120 121 Any widget kcontrols can be set using the controls and num_controls members. 122 123 e.g. Mixer widget (the kcontrols are declared first) 124 125 /* Output Mixer */ 126 static const snd_kcontrol_new_t wm8731_output_mixer_controls[] = { 127 SOC_DAPM_SINGLE("Line Bypass Switch", WM8731_APANA, 3, 1, 0), 128 SOC_DAPM_SINGLE("Mic Sidetone Switch", WM8731_APANA, 5, 1, 0), 129 SOC_DAPM_SINGLE("HiFi Playback Switch", WM8731_APANA, 4, 1, 0), 130 }; 131 132 SND_SOC_DAPM_MIXER("Output Mixer", WM8731_PWR, 4, 1, wm8731_output_mixer_controls, 133 ARRAY_SIZE(wm8731_output_mixer_controls)), 134 135 If you don't want the mixer elements prefixed with the name of the mixer widget, 136 you can use SND_SOC_DAPM_MIXER_NAMED_CTL instead. the parameters are the same 137 as for SND_SOC_DAPM_MIXER. 138 139 140 2.3 Machine domain Widgets 141 -------------------------- 142 143 Machine widgets are different from codec widgets in that they don't have a 144 codec register bit associated with them. A machine widget is assigned to each 145 machine audio component (non codec or DSP) that can be independently 146 powered. e.g. 147 148 o Speaker Amp 149 o Microphone Bias 150 o Jack connectors 151 152 A machine widget can have an optional call back. 153 154 e.g. Jack connector widget for an external Mic that enables Mic Bias 155 when the Mic is inserted:- 156 157 static int spitz_mic_bias(struct snd_soc_dapm_widget* w, int event) 158 { 159 gpio_set_value(SPITZ_GPIO_MIC_BIAS, SND_SOC_DAPM_EVENT_ON(event)); 160 return 0; 161 } 162 163 SND_SOC_DAPM_MIC("Mic Jack", spitz_mic_bias), 164 165 166 2.4 Codec (BIAS) Domain 167 ----------------------- 168 169 The codec bias power domain has no widgets and is handled by the codecs DAPM 170 event handler. This handler is called when the codec powerstate is changed wrt 171 to any stream event or by kernel PM events. 172 173 174 2.5 Virtual Widgets 175 ------------------- 176 177 Sometimes widgets exist in the codec or machine audio map that don't have any 178 corresponding soft power control. In this case it is necessary to create 179 a virtual widget - a widget with no control bits e.g. 180 181 SND_SOC_DAPM_MIXER("AC97 Mixer", SND_SOC_DAPM_NOPM, 0, 0, NULL, 0), 182 183 This can be used to merge to signal paths together in software. 184 185 After all the widgets have been defined, they can then be added to the DAPM 186 subsystem individually with a call to snd_soc_dapm_new_control(). 187 188 189 3. Codec/DSP Widget Interconnections 190 ==================================== 191 192 Widgets are connected to each other within the codec, platform and machine by 193 audio paths (called interconnections). Each interconnection must be defined in 194 order to create a map of all audio paths between widgets. 195 196 This is easiest with a diagram of the codec or DSP (and schematic of the machine 197 audio system), as it requires joining widgets together via their audio signal 198 paths. 199 200 e.g., from the WM8731 output mixer (wm8731.c) 201 202 The WM8731 output mixer has 3 inputs (sources) 203 204 1. Line Bypass Input 205 2. DAC (HiFi playback) 206 3. Mic Sidetone Input 207 208 Each input in this example has a kcontrol associated with it (defined in example 209 above) and is connected to the output mixer via its kcontrol name. We can now 210 connect the destination widget (wrt audio signal) with its source widgets. 211 212 /* output mixer */ 213 {"Output Mixer", "Line Bypass Switch", "Line Input"}, 214 {"Output Mixer", "HiFi Playback Switch", "DAC"}, 215 {"Output Mixer", "Mic Sidetone Switch", "Mic Bias"}, 216 217 So we have :- 218 219 Destination Widget <=== Path Name <=== Source Widget 220 221 Or:- 222 223 Sink, Path, Source 224 225 Or :- 226 227 "Output Mixer" is connected to the "DAC" via the "HiFi Playback Switch". 228 229 When there is no path name connecting widgets (e.g. a direct connection) we 230 pass NULL for the path name. 231 232 Interconnections are created with a call to:- 233 234 snd_soc_dapm_connect_input(codec, sink, path, source); 235 236 Finally, snd_soc_dapm_new_widgets(codec) must be called after all widgets and 237 interconnections have been registered with the core. This causes the core to 238 scan the codec and machine so that the internal DAPM state matches the 239 physical state of the machine. 240 241 242 3.1 Machine Widget Interconnections 243 ----------------------------------- 244 Machine widget interconnections are created in the same way as codec ones and 245 directly connect the codec pins to machine level widgets. 246 247 e.g. connects the speaker out codec pins to the internal speaker. 248 249 /* ext speaker connected to codec pins LOUT2, ROUT2 */ 250 {"Ext Spk", NULL , "ROUT2"}, 251 {"Ext Spk", NULL , "LOUT2"}, 252 253 This allows the DAPM to power on and off pins that are connected (and in use) 254 and pins that are NC respectively. 255 256 257 4 Endpoint Widgets 258 =================== 259 An endpoint is a start or end point (widget) of an audio signal within the 260 machine and includes the codec. e.g. 261 262 o Headphone Jack 263 o Internal Speaker 264 o Internal Mic 265 o Mic Jack 266 o Codec Pins 267 268 Endpoints are added to the DAPM graph so that their usage can be determined in 269 order to save power. e.g. NC codecs pins will be switched OFF, unconnected 270 jacks can also be switched OFF. 271 272 273 5 DAPM Widget Events 274 ==================== 275 276 Some widgets can register their interest with the DAPM core in PM events. 277 e.g. A Speaker with an amplifier registers a widget so the amplifier can be 278 powered only when the spk is in use. 279 280 /* turn speaker amplifier on/off depending on use */ 281 static int corgi_amp_event(struct snd_soc_dapm_widget *w, int event) 282 { 283 gpio_set_value(CORGI_GPIO_APM_ON, SND_SOC_DAPM_EVENT_ON(event)); 284 return 0; 285 } 286 287 /* corgi machine dapm widgets */ 288 static const struct snd_soc_dapm_widget wm8731_dapm_widgets = 289 SND_SOC_DAPM_SPK("Ext Spk", corgi_amp_event); 290 291 Please see soc-dapm.h for all other widgets that support events. 292 293 294 5.1 Event types 295 --------------- 296 297 The following event types are supported by event widgets. 298 299 /* dapm event types */ 300 #define SND_SOC_DAPM_PRE_PMU 0x1 /* before widget power up */ 301 #define SND_SOC_DAPM_POST_PMU 0x2 /* after widget power up */ 302 #define SND_SOC_DAPM_PRE_PMD 0x4 /* before widget power down */ 303 #define SND_SOC_DAPM_POST_PMD 0x8 /* after widget power down */ 304 #define SND_SOC_DAPM_PRE_REG 0x10 /* before audio path setup */ 305 #define SND_SOC_DAPM_POST_REG 0x20 /* after audio path setup */