1 ==============================================
2 Creating codec to codec dai link for ALSA dapm
3 ==============================================
4
5 Mostly the flow of audio is always from CPU to codec so your system
6 will look as below:
7 ::
8
9 --------- ---------
10 | | dai | |
11 CPU -------> codec
12 | | | |
13 --------- ---------
14
15 In case your system looks as below:
16 ::
17
18 ---------
19 | |
20 codec-2
21 | |
22 ---------
23 |
24 dai-2
25 |
26 ---------- ---------
27 | | dai-1 | |
28 CPU -------> codec-1
29 | | | |
30 ---------- ---------
31 |
32 dai-3
33 |
34 ---------
35 | |
36 codec-3
37 | |
38 ---------
39
40 Suppose codec-2 is a bluetooth chip and codec-3 is connected to
41 a speaker and you have a below scenario:
42 codec-2 will receive the audio data and the user wants to play that
43 audio through codec-3 without involving the CPU.This
44 aforementioned case is the ideal case when codec to codec
45 connection should be used.
46
47 Your dai_link should appear as below in your machine
48 file:
49 ::
50
51 /*
52 * this pcm stream only supports 24 bit, 2 channel and
53 * 48k sampling rate.
54 */
55 static const struct snd_soc_pcm_stream dsp_codec_params = {
56 .formats = SNDRV_PCM_FMTBIT_S24_LE,
57 .rate_min = 48000,
58 .rate_max = 48000,
59 .channels_min = 2,
60 .channels_max = 2,
61 };
62
63 {
64 .name = "CPU-DSP",
65 .stream_name = "CPU-DSP",
66 .cpu_dai_name = "samsung-i2s.0",
67 .codec_name = "codec-2,
68 .codec_dai_name = "codec-2-dai_name",
69 .platform_name = "samsung-i2s.0",
70 .dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF
71 | SND_SOC_DAIFMT_CBM_CFM,
72 .ignore_suspend = 1,
73 .c2c_params = &dsp_codec_params,
74 .num_c2c_params = 1,
75 },
76 {
77 .name = "DSP-CODEC",
78 .stream_name = "DSP-CODEC",
79 .cpu_dai_name = "wm0010-sdi2",
80 .codec_name = "codec-3,
81 .codec_dai_name = "codec-3-dai_name",
82 .dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF
83 | SND_SOC_DAIFMT_CBM_CFM,
84 .ignore_suspend = 1,
85 .c2c_params = &dsp_codec_params,
86 .num_c2c_params = 1,
87 },
88
89 Above code snippet is motivated from sound/soc/samsung/speyside.c.
90
91 Note the "c2c_params" callback which lets the dapm know that this
92 dai_link is a codec to codec connection.
93
94 In dapm core a route is created between cpu_dai playback widget
95 and codec_dai capture widget for playback path and vice-versa is
96 true for capture path. In order for this aforementioned route to get
97 triggered, DAPM needs to find a valid endpoint which could be either
98 a sink or source widget corresponding to playback and capture path
99 respectively.
100
101 In order to trigger this dai_link widget, a thin codec driver for
102 the speaker amp can be created as demonstrated in wm8727.c file, it
103 sets appropriate constraints for the device even if it needs no control.
104
105 Make sure to name your corresponding cpu and codec playback and capture
106 dai names ending with "Playback" and "Capture" respectively as dapm core
107 will link and power those dais based on the name.
108
109 A dai_link in a "simple-audio-card" will automatically be detected as
110 codec to codec when all DAIs on the link belong to codec components.
111 The dai_link will be initialized with the subset of stream parameters
112 (channels, format, sample rate) supported by all DAIs on the link. Since
113 there is no way to provide these parameters in the device tree, this is
114 mostly useful for communication with simple fixed-function codecs, such
115 as a Bluetooth controller or cellular modem.
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