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