1 ===========
2 Dynamic PCM
3 ===========
4
5 Description
6 ===========
7
8 Dynamic PCM allows an ALSA PCM device to digit
9 various digital endpoints during the PCM strea
10 digital audio to I2S DAI0, I2S DAI1 or PDM DAI
11 drivers that expose several ALSA PCMs and can
12
13 The DPCM runtime routing is determined by the
14 way as the analog signal is routed in an ASoC
15 graph representing the DSP internal audio path
16 determine the path used by each ALSA PCM.
17
18 DPCM re-uses all the existing component codec,
19 any modifications.
20
21
22 Phone Audio System with SoC based DSP
23 -------------------------------------
24
25 Consider the following phone audio subsystem.
26 document for all examples :-
27 ::
28
29 | Front End PCMs | SoC DSP | Back End D
30
31 *************
32 PCM0 <------------> * * <----DAI0-
33 * *
34 PCM1 <------------> * * <----DAI1-
35 * DSP *
36 PCM2 <------------> * * <----DAI2-
37 * *
38 PCM3 <------------> * * <----DAI3-
39 * *
40 * * <----DAI4-
41 * *
42 * * <----DAI5-
43 *************
44
45 This diagram shows a simple smart phone audio
46 FM digital radio, Speakers, Headset Jack, digi
47 modem. This sound card exposes 4 DSP front end
48 supports 6 back end (BE) DAIs. Each FE PCM can
49 of the BE DAIs. The FE PCM devices can also ro
50
51
52
53 Example - DPCM Switching playback from DAI0 to
54 ----------------------------------------------
55
56 Audio is being played to the Headset. After a
57 and audio continues playing on the speakers.
58
59 Playback on PCM0 to Headset would look like :-
60 ::
61
62 *************
63 PCM0 <============> * * <====DAI0=
64 * *
65 PCM1 <------------> * * <----DAI1-
66 * DSP *
67 PCM2 <------------> * * <----DAI2-
68 * *
69 PCM3 <------------> * * <----DAI3-
70 * *
71 * * <----DAI4-
72 * *
73 * * <----DAI5-
74 *************
75
76 The headset is removed from the jack by user s
77 ::
78
79 *************
80 PCM0 <============> * * <----DAI0-
81 * *
82 PCM1 <------------> * * <====DAI1=
83 * DSP *
84 PCM2 <------------> * * <----DAI2-
85 * *
86 PCM3 <------------> * * <----DAI3-
87 * *
88 * * <----DAI4-
89 * *
90 * * <----DAI5-
91 *************
92
93 The audio driver processes this as follows :-
94
95 1. Machine driver receives Jack removal event.
96
97 2. Machine driver OR audio HAL disables the He
98
99 3. DPCM runs the PCM trigger(stop), hw_free(),
100 for headset since the path is now disabled.
101
102 4. Machine driver or audio HAL enables the spe
103
104 5. DPCM runs the PCM ops for startup(), hw_par
105 trigger(start) for DAI1 Speakers since the
106
107 In this example, the machine driver or userspa
108 and then DPCM will take care of managing the D
109 the link up or down. Audio playback does not s
110
111
112
113 DPCM machine driver
114 ===================
115
116 The DPCM enabled ASoC machine driver is simila
117 except that we also have to :-
118
119 1. Define the FE and BE DAI links.
120
121 2. Define any FE/BE PCM operations.
122
123 3. Define widget graph connections.
124
125
126 FE and BE DAI links
127 -------------------
128 ::
129
130 | Front End PCMs | SoC DSP | Back End D
131
132 *************
133 PCM0 <------------> * * <----DAI0-
134 * *
135 PCM1 <------------> * * <----DAI1-
136 * DSP *
137 PCM2 <------------> * * <----DAI2-
138 * *
139 PCM3 <------------> * * <----DAI3-
140 * *
141 * * <----DAI4-
142 * *
143 * * <----DAI5-
144 *************
145
146 For the example above we have to define 4 FE D
147 FE DAI links are defined as follows :-
148 ::
149
150 static struct snd_soc_dai_link machine_dais[
151 {
152 .name = "PCM0 System",
153 .stream_name = "System Playbac
154 .cpu_dai_name = "System Pin",
155 .platform_name = "dsp-audio",
156 .codec_name = "snd-soc-dummy",
157 .codec_dai_name = "snd-soc-dum
158 .dynamic = 1,
159 .trigger = {SND_SOC_DPCM_TRIGG
160 .dpcm_playback = 1,
161 },
162 .....< other FE and BE DAI links here
163 };
164
165 This FE DAI link is pretty similar to a regula
166 set the DAI link to a DPCM FE with the ``dynam
167 directions should also be set with the ``dpcm_
168 flags. There is also an option to specify the
169 each FE. This allows the ASoC core to trigger
170 components (as some DSPs have strong requireme
171 start and stop sequences).
172
173 The FE DAI above sets the codec and code DAIs
174 dynamic and will change depending on runtime c
175
176 The BE DAIs are configured as follows :-
177 ::
178
179 static struct snd_soc_dai_link machine_dais[
180 .....< FE DAI links here >
181 {
182 .name = "Codec Headset",
183 .cpu_dai_name = "ssp-dai.0",
184 .platform_name = "snd-soc-dumm
185 .no_pcm = 1,
186 .codec_name = "rt5640.0-001c",
187 .codec_dai_name = "rt5640-aif1
188 .ignore_suspend = 1,
189 .ignore_pmdown_time = 1,
190 .be_hw_params_fixup = hswult_s
191 .ops = &haswell_ops,
192 .dpcm_playback = 1,
193 .dpcm_capture = 1,
194 },
195 .....< other BE DAI links here >
196 };
197
198 This BE DAI link connects DAI0 to the codec (i
199 the ``no_pcm`` flag to mark it has a BE and se
200 directions using ``dpcm_playback`` and ``dpcm_
201
202 The BE has also flags set for ignoring suspend
203 the BE to work in a hostless mode where the ho
204 like a BT phone call :-
205 ::
206
207 *************
208 PCM0 <------------> * * <----DAI0-
209 * *
210 PCM1 <------------> * * <----DAI1-
211 * DSP *
212 PCM2 <------------> * * <====DAI2=
213 * *
214 PCM3 <------------> * * <====DAI3=
215 * *
216 * * <----DAI4-
217 * *
218 * * <----DAI5-
219 *************
220
221 This allows the host CPU to sleep while the DS
222 still in operation.
223
224 A BE DAI link can also set the codec to a dumm
225 that is managed externally.
226
227 Likewise a BE DAI can also set a dummy cpu DAI
228 DSP firmware.
229
230
231 FE/BE PCM operations
232 --------------------
233
234 The BE above also exports some PCM operations
235 callback is used by the machine driver to (re)
236 FE hw params. i.e. the DSP may perform SRC or
237
238 e.g. DSP converts all FE hw params to run at f
239 DAI0. This means all FE hw_params have to be f
240 DAI0 so that the DAI is running at desired con
241 configuration.
242 ::
243
244 static int dai0_fixup(struct snd_soc_pcm_run
245 struct snd_pcm_hw_para
246 {
247 struct snd_interval *rate = hw_param_i
248 SNDRV_PCM_HW_PARAM_RAT
249 struct snd_interval *channels = hw_par
250
251
252 /* The DSP will convert the FE rate to
253 rate->min = rate->max = 48000;
254 channels->min = channels->max = 2;
255
256 /* set DAI0 to 16 bit */
257 params_set_format(params, SNDRV_PCM_FO
258 return 0;
259 }
260
261 The other PCM operation are the same as for re
262
263
264 Widget graph connections
265 ------------------------
266
267 The BE DAI links will normally be connected to
268 by the ASoC DAPM core. However, if the BE code
269 has to be set explicitly in the driver :-
270 ::
271
272 /* BE for codec Headset - DAI0 is dummy and
273 {"DAI0 CODEC IN", NULL, "AIF1 Capture"},
274 {"AIF1 Playback", NULL, "DAI0 CODEC OUT"},
275
276
277 Writing a DPCM DSP driver
278 =========================
279
280 The DPCM DSP driver looks much like a standard
281 combined with elements from a codec class driv
282 implement :-
283
284 1. Front End PCM DAIs - i.e. struct snd_soc_da
285
286 2. DAPM graph showing DSP audio routing from F
287
288 3. DAPM widgets from DSP graph.
289
290 4. Mixers for gains, routing, etc.
291
292 5. DMA configuration.
293
294 6. BE AIF widgets.
295
296 Items 6 is important for routing the audio out
297 defined for each BE and each stream direction.
298 have :-
299 ::
300
301 SND_SOC_DAPM_AIF_IN("DAI0 RX", NULL, 0, SND_
302 SND_SOC_DAPM_AIF_OUT("DAI0 TX", NULL, 0, SND
303
304 The BE AIF are used to connect the DSP graph t
305 component drivers (e.g. codec graph).
306
307
308 Hostless PCM streams
309 ====================
310
311 A hostless PCM stream is a stream that is not
312 example of this would be a phone call from han
313 ::
314
315 *************
316 PCM0 <------------> * * <----DAI0-
317 * *
318 PCM1 <------------> * * <====DAI1=
319 * DSP *
320 PCM2 <------------> * * <====DAI2=
321 * *
322 PCM3 <------------> * * <----DAI3-
323 * *
324 * * <----DAI4-
325 * *
326 * * <----DAI5-
327 *************
328
329 In this case the PCM data is routed via the DS
330 is only used for control and can sleep during
331
332 The host can control the hostless link either
333
334 1. Configuring the link as a CODEC <-> CODEC
335 is enabled or disabled by the state of the
336 there is a mixer control that can be used
337 between both DAIs.
338
339 2. Hostless FE. This FE has a virtual connect
340 graph. Control is then carried out by the
341 This method gives more control over the DA
342 userspace code to control the link. Its re
343 unless your HW needs more fine grained seq
344
345
346 CODEC <-> CODEC link
347 --------------------
348
349 This DAI link is enabled when DAPM detects a v
350 The machine driver sets some additional parame
351 ::
352
353 static const struct snd_soc_pcm_stream dai_p
354 .formats = SNDRV_PCM_FMTBIT_S32_LE,
355 .rate_min = 8000,
356 .rate_max = 8000,
357 .channels_min = 2,
358 .channels_max = 2,
359 };
360
361 static struct snd_soc_dai_link dais[] = {
362 < ... more DAI links above ... >
363 {
364 .name = "MODEM",
365 .stream_name = "MODEM",
366 .cpu_dai_name = "dai2",
367 .codec_dai_name = "modem-aif1"
368 .codec_name = "modem",
369 .dai_fmt = SND_SOC_DAIFMT_I2S
370 | SND_SOC_DAIF
371 .c2c_params = &dai_params,
372 .num_c2c_params = 1,
373 }
374 < ... more DAI links here ... >
375
376 These parameters are used to configure the DAI
377 valid path and then calls the PCM operations t
378 call the appropriate PCM operations to disable
379 longer valid.
380
381
382 Hostless FE
383 -----------
384
385 The DAI link(s) are enabled by a FE that does
386 This means creating a new FE that is connected
387 DAI links. The DAI links will be started when
388 when the FE PCM is stopped. Note that the FE P
389 this configuration.
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