1 ===================================================
2 Dynamic Audio Power Management for Portable Devices
3 ===================================================
4
5 Description
6 ===========
7
8 Dynamic Audio Power Management (DAPM) is designed to allow portable
9 Linux devices to use the minimum amount of power within the audio
10 subsystem at all times. It is independent of other kernel power
11 management frameworks and, as such, can easily co-exist with them.
12
13 DAPM is also completely transparent to all user space applications as
14 all power switching is done within the ASoC core. No code changes or
15 recompiling are required for user space applications. DAPM makes power
16 switching decisions based upon any audio stream (capture/playback)
17 activity and audio mixer settings within the device.
18
19 DAPM is based on two basic elements, called widgets and routes:
20
21 * a **widget** is every part of the audio hardware that can be enabled by
22 software when in use and disabled to save power when not in use
23 * a **route** is an interconnection between widgets that exists when sound
24 can flow from one widget to the other
25
26 All DAPM power switching decisions are made automatically by consulting an
27 audio routing graph. This graph is specific to each sound card and spans
28 the whole sound card, so some DAPM routes connect two widgets belonging to
29 different components (e.g. the LINE OUT pin of a CODEC and the input pin of
30 an amplifier).
31
32 The graph for the STM32MP1-DK1 sound card is shown in picture:
33
34 .. kernel-figure:: dapm-graph.svg
35 :alt: Example DAPM graph
36 :align: center
37
38 DAPM power domains
39 ==================
40
41 There are 4 power domains within DAPM:
42
43 Codec bias domain
44 VREF, VMID (core codec and audio power)
45
46 Usually controlled at codec probe/remove and suspend/resume, although
47 can be set at stream time if power is not needed for sidetone, etc.
48
49 Platform/Machine domain
50 physically connected inputs and outputs
51
52 Is platform/machine and user action specific, is configured by the
53 machine driver and responds to asynchronous events e.g when HP
54 are inserted
55
56 Path domain
57 audio subsystem signal paths
58
59 Automatically set when mixer and mux settings are changed by the user.
60 e.g. alsamixer, amixer.
61
62 Stream domain
63 DACs and ADCs.
64
65 Enabled and disabled when stream playback/capture is started and
66 stopped respectively. e.g. aplay, arecord.
67
68
69 DAPM Widgets
70 ============
71
72 Audio DAPM widgets fall into a number of types:
73
74 Mixer
75 Mixes several analog signals into a single analog signal.
76 Mux
77 An analog switch that outputs only one of many inputs.
78 PGA
79 A programmable gain amplifier or attenuation widget.
80 ADC
81 Analog to Digital Converter
82 DAC
83 Digital to Analog Converter
84 Switch
85 An analog switch
86 Input
87 A codec input pin
88 Output
89 A codec output pin
90 Headphone
91 Headphone (and optional Jack)
92 Mic
93 Mic (and optional Jack)
94 Line
95 Line Input/Output (and optional Jack)
96 Speaker
97 Speaker
98 Supply
99 Power or clock supply widget used by other widgets.
100 Regulator
101 External regulator that supplies power to audio components.
102 Clock
103 External clock that supplies clock to audio components.
104 AIF IN
105 Audio Interface Input (with TDM slot mask).
106 AIF OUT
107 Audio Interface Output (with TDM slot mask).
108 Siggen
109 Signal Generator.
110 DAI IN
111 Digital Audio Interface Input.
112 DAI OUT
113 Digital Audio Interface Output.
114 DAI Link
115 DAI Link between two DAI structures
116 Pre
117 Special PRE widget (exec before all others)
118 Post
119 Special POST widget (exec after all others)
120 Buffer
121 Inter widget audio data buffer within a DSP.
122 Scheduler
123 DSP internal scheduler that schedules component/pipeline processing
124 work.
125 Effect
126 Widget that performs an audio processing effect.
127 SRC
128 Sample Rate Converter within DSP or CODEC
129 ASRC
130 Asynchronous Sample Rate Converter within DSP or CODEC
131 Encoder
132 Widget that encodes audio data from one format (usually PCM) to another
133 usually more compressed format.
134 Decoder
135 Widget that decodes audio data from a compressed format to an
136 uncompressed format like PCM.
137
138
139 (Widgets are defined in include/sound/soc-dapm.h)
140
141 Widgets can be added to the sound card by any of the component driver types.
142 There are convenience macros defined in soc-dapm.h that can be used to quickly
143 build a list of widgets of the codecs and machines DAPM widgets.
144
145 Most widgets have a name, register, shift and invert. Some widgets have extra
146 parameters for stream name and kcontrols.
147
148
149 Stream Domain Widgets
150 ---------------------
151
152 Stream Widgets relate to the stream power domain and only consist of ADCs
153 (analog to digital converters), DACs (digital to analog converters),
154 AIF IN and AIF OUT.
155
156 Stream widgets have the following format:
157 ::
158
159 SND_SOC_DAPM_DAC(name, stream name, reg, shift, invert),
160 SND_SOC_DAPM_AIF_IN(name, stream, slot, reg, shift, invert)
161
162 NOTE: the stream name must match the corresponding stream name in your codec
163 snd_soc_dai_driver.
164
165 e.g. stream widgets for HiFi playback and capture
166 ::
167
168 SND_SOC_DAPM_DAC("HiFi DAC", "HiFi Playback", REG, 3, 1),
169 SND_SOC_DAPM_ADC("HiFi ADC", "HiFi Capture", REG, 2, 1),
170
171 e.g. stream widgets for AIF
172 ::
173
174 SND_SOC_DAPM_AIF_IN("AIF1RX", "AIF1 Playback", 0, SND_SOC_NOPM, 0, 0),
175 SND_SOC_DAPM_AIF_OUT("AIF1TX", "AIF1 Capture", 0, SND_SOC_NOPM, 0, 0),
176
177
178 Path Domain Widgets
179 -------------------
180
181 Path domain widgets have a ability to control or affect the audio signal or
182 audio paths within the audio subsystem. They have the following form:
183 ::
184
185 SND_SOC_DAPM_PGA(name, reg, shift, invert, controls, num_controls)
186
187 Any widget kcontrols can be set using the controls and num_controls members.
188
189 e.g. Mixer widget (the kcontrols are declared first)
190 ::
191
192 /* Output Mixer */
193 static const snd_kcontrol_new_t wm8731_output_mixer_controls[] = {
194 SOC_DAPM_SINGLE("Line Bypass Switch", WM8731_APANA, 3, 1, 0),
195 SOC_DAPM_SINGLE("Mic Sidetone Switch", WM8731_APANA, 5, 1, 0),
196 SOC_DAPM_SINGLE("HiFi Playback Switch", WM8731_APANA, 4, 1, 0),
197 };
198
199 SND_SOC_DAPM_MIXER("Output Mixer", WM8731_PWR, 4, 1, wm8731_output_mixer_controls,
200 ARRAY_SIZE(wm8731_output_mixer_controls)),
201
202 If you don't want the mixer elements prefixed with the name of the mixer widget,
203 you can use SND_SOC_DAPM_MIXER_NAMED_CTL instead. the parameters are the same
204 as for SND_SOC_DAPM_MIXER.
205
206
207 Machine domain Widgets
208 ----------------------
209
210 Machine widgets are different from codec widgets in that they don't have a
211 codec register bit associated with them. A machine widget is assigned to each
212 machine audio component (non codec or DSP) that can be independently
213 powered. e.g.
214
215 * Speaker Amp
216 * Microphone Bias
217 * Jack connectors
218
219 A machine widget can have an optional call back.
220
221 e.g. Jack connector widget for an external Mic that enables Mic Bias
222 when the Mic is inserted::
223
224 static int spitz_mic_bias(struct snd_soc_dapm_widget* w, int event)
225 {
226 gpio_set_value(SPITZ_GPIO_MIC_BIAS, SND_SOC_DAPM_EVENT_ON(event));
227 return 0;
228 }
229
230 SND_SOC_DAPM_MIC("Mic Jack", spitz_mic_bias),
231
232
233 Codec (BIAS) Domain
234 -------------------
235
236 The codec bias power domain has no widgets and is handled by the codec DAPM
237 event handler. This handler is called when the codec powerstate is changed wrt
238 to any stream event or by kernel PM events.
239
240
241 Virtual Widgets
242 ---------------
243
244 Sometimes widgets exist in the codec or machine audio graph that don't have any
245 corresponding soft power control. In this case it is necessary to create
246 a virtual widget - a widget with no control bits e.g.
247 ::
248
249 SND_SOC_DAPM_MIXER("AC97 Mixer", SND_SOC_NOPM, 0, 0, NULL, 0),
250
251 This can be used to merge two signal paths together in software.
252
253 Registering DAPM controls
254 =========================
255
256 In many cases the DAPM widgets are implemented statically in a ``static
257 const struct snd_soc_dapm_widget`` array in a codec driver, and simply
258 declared via the ``dapm_widgets`` and ``num_dapm_widgets`` fields of the
259 ``struct snd_soc_component_driver``.
260
261 Similarly, routes connecting them are implemented statically in a ``static
262 const struct snd_soc_dapm_route`` array and declared via the
263 ``dapm_routes`` and ``num_dapm_routes`` fields of the same struct.
264
265 With the above declared, the driver registration will take care of
266 populating them::
267
268 static const struct snd_soc_dapm_widget wm2000_dapm_widgets[] = {
269 SND_SOC_DAPM_OUTPUT("SPKN"),
270 SND_SOC_DAPM_OUTPUT("SPKP"),
271 ...
272 };
273
274 /* Target, Path, Source */
275 static const struct snd_soc_dapm_route wm2000_audio_map[] = {
276 { "SPKN", NULL, "ANC Engine" },
277 { "SPKP", NULL, "ANC Engine" },
278 ...
279 };
280
281 static const struct snd_soc_component_driver soc_component_dev_wm2000 = {
282 ...
283 .dapm_widgets = wm2000_dapm_widgets,
284 .num_dapm_widgets = ARRAY_SIZE(wm2000_dapm_widgets),
285 .dapm_routes = wm2000_audio_map,
286 .num_dapm_routes = ARRAY_SIZE(wm2000_audio_map),
287 ...
288 };
289
290 In more complex cases the list of DAPM widgets and/or routes can be only
291 known at probe time. This happens for example when a driver supports
292 different models having a different set of features. In those cases
293 separate widgets and routes arrays implementing the case-specific features
294 can be registered programmatically by calling snd_soc_dapm_new_controls()
295 and snd_soc_dapm_add_routes().
296
297
298 Codec/DSP Widget Interconnections
299 =================================
300
301 Widgets are connected to each other within the codec, platform and machine by
302 audio paths (called interconnections). Each interconnection must be defined in
303 order to create a graph of all audio paths between widgets.
304
305 This is easiest with a diagram of the codec or DSP (and schematic of the machine
306 audio system), as it requires joining widgets together via their audio signal
307 paths.
308
309 For example the WM8731 output mixer (wm8731.c) has 3 inputs (sources):
310
311 1. Line Bypass Input
312 2. DAC (HiFi playback)
313 3. Mic Sidetone Input
314
315 Each input in this example has a kcontrol associated with it (defined in
316 the example above) and is connected to the output mixer via its kcontrol
317 name. We can now connect the destination widget (wrt audio signal) with its
318 source widgets. ::
319
320 /* output mixer */
321 {"Output Mixer", "Line Bypass Switch", "Line Input"},
322 {"Output Mixer", "HiFi Playback Switch", "DAC"},
323 {"Output Mixer", "Mic Sidetone Switch", "Mic Bias"},
324
325 So we have:
326
327 * Destination Widget <=== Path Name <=== Source Widget, or
328 * Sink, Path, Source, or
329 * ``Output Mixer`` is connected to the ``DAC`` via the ``HiFi Playback Switch``.
330
331 When there is no path name connecting widgets (e.g. a direct connection) we
332 pass NULL for the path name.
333
334 Interconnections are created with a call to::
335
336 snd_soc_dapm_connect_input(codec, sink, path, source);
337
338 Finally, snd_soc_dapm_new_widgets() must be called after all widgets and
339 interconnections have been registered with the core. This causes the core to
340 scan the codec and machine so that the internal DAPM state matches the
341 physical state of the machine.
342
343
344 Machine Widget Interconnections
345 -------------------------------
346 Machine widget interconnections are created in the same way as codec ones and
347 directly connect the codec pins to machine level widgets.
348
349 e.g. connects the speaker out codec pins to the internal speaker.
350 ::
351
352 /* ext speaker connected to codec pins LOUT2, ROUT2 */
353 {"Ext Spk", NULL , "ROUT2"},
354 {"Ext Spk", NULL , "LOUT2"},
355
356 This allows the DAPM to power on and off pins that are connected (and in use)
357 and pins that are NC respectively.
358
359
360 Endpoint Widgets
361 ================
362 An endpoint is a start or end point (widget) of an audio signal within the
363 machine and includes the codec. e.g.
364
365 * Headphone Jack
366 * Internal Speaker
367 * Internal Mic
368 * Mic Jack
369 * Codec Pins
370
371 Endpoints are added to the DAPM graph so that their usage can be determined in
372 order to save power. e.g. NC codecs pins will be switched OFF, unconnected
373 jacks can also be switched OFF.
374
375
376 DAPM Widget Events
377 ==================
378
379 Widgets needing to implement a more complex behaviour than what DAPM can do
380 can set a custom "event handler" by setting a function pointer. An example
381 is a power supply needing to enable a GPIO::
382
383 static int sof_es8316_speaker_power_event(struct snd_soc_dapm_widget *w,
384 struct snd_kcontrol *kcontrol, int event)
385 {
386 if (SND_SOC_DAPM_EVENT_ON(event))
387 gpiod_set_value_cansleep(gpio_pa, true);
388 else
389 gpiod_set_value_cansleep(gpio_pa, false);
390
391 return 0;
392 }
393
394 static const struct snd_soc_dapm_widget st_widgets[] = {
395 ...
396 SND_SOC_DAPM_SUPPLY("Speaker Power", SND_SOC_NOPM, 0, 0,
397 sof_es8316_speaker_power_event,
398 SND_SOC_DAPM_PRE_PMD | SND_SOC_DAPM_POST_PMU),
399 };
400
401 See soc-dapm.h for all other widgets that support events.
402
403
404 Event types
405 -----------
406
407 The following event types are supported by event widgets::
408
409 /* dapm event types */
410 #define SND_SOC_DAPM_PRE_PMU 0x1 /* before widget power up */
411 #define SND_SOC_DAPM_POST_PMU 0x2 /* after widget power up */
412 #define SND_SOC_DAPM_PRE_PMD 0x4 /* before widget power down */
413 #define SND_SOC_DAPM_POST_PMD 0x8 /* after widget power down */
414 #define SND_SOC_DAPM_PRE_REG 0x10 /* before audio path setup */
415 #define SND_SOC_DAPM_POST_REG 0x20 /* after audio path setup */
416 #define SND_SOC_DAPM_WILL_PMU 0x40 /* called at start of sequence */
417 #define SND_SOC_DAPM_WILL_PMD 0x80 /* called at start of sequence */
418 #define SND_SOC_DAPM_PRE_POST_PMD (SND_SOC_DAPM_PRE_PMD | SND_SOC_DAPM_POST_PMD)
419 #define SND_SOC_DAPM_PRE_POST_PMU (SND_SOC_DAPM_PRE_PMU | SND_SOC_DAPM_POST_PMU)
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