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authorTakashi Iwai <tiwai@suse.de>2016-11-11 17:34:57 +0100
committerTakashi Iwai <tiwai@suse.de>2016-11-11 17:34:57 +0100
commit76228a2b541daebcc8f6d5d7dd65bdea90d173f1 (patch)
treef1df9b7b63b39282d52cafc5988513853ce465e9 /Documentation/sound
parent40433cd34e280bd1a56f54a3898e86863814c824 (diff)
parent452a256898e7ca88115aa02d3851e67994ce3e19 (diff)
Merge branch 'topic/doc' of git://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound into topic/restize-docs
Diffstat (limited to 'Documentation/sound')
-rw-r--r--Documentation/sound/alsa/soc/codec_to_codec.txt103
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diff --git a/Documentation/sound/alsa/soc/codec_to_codec.txt b/Documentation/sound/alsa/soc/codec_to_codec.txt
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+Creating codec to codec dai link for ALSA dapm
+===================================================
+
+Mostly the flow of audio is always from CPU to codec so your system
+will look as below:
+
+ --------- ---------
+| | dai | |
+ CPU -------> codec
+| | | |
+ --------- ---------
+
+In case your system looks as below:
+ ---------
+ | |
+ codec-2
+ | |
+ ---------
+ |
+ dai-2
+ |
+ ---------- ---------
+| | dai-1 | |
+ CPU -------> codec-1
+| | | |
+ ---------- ---------
+ |
+ dai-3
+ |
+ ---------
+ | |
+ codec-3
+ | |
+ ---------
+
+Suppose codec-2 is a bluetooth chip and codec-3 is connected to
+a speaker and you have a below scenario:
+codec-2 will receive the audio data and the user wants to play that
+audio through codec-3 without involving the CPU.This
+aforementioned case is the ideal case when codec to codec
+connection should be used.
+
+Your dai_link should appear as below in your machine
+file:
+
+/*
+ * this pcm stream only supports 24 bit, 2 channel and
+ * 48k sampling rate.
+ */
+static const struct snd_soc_pcm_stream dsp_codec_params = {
+ .formats = SNDRV_PCM_FMTBIT_S24_LE,
+ .rate_min = 48000,
+ .rate_max = 48000,
+ .channels_min = 2,
+ .channels_max = 2,
+};
+
+{
+ .name = "CPU-DSP",
+ .stream_name = "CPU-DSP",
+ .cpu_dai_name = "samsung-i2s.0",
+ .codec_name = "codec-2,
+ .codec_dai_name = "codec-2-dai_name",
+ .platform_name = "samsung-i2s.0",
+ .dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF
+ | SND_SOC_DAIFMT_CBM_CFM,
+ .ignore_suspend = 1,
+ .params = &dsp_codec_params,
+},
+{
+ .name = "DSP-CODEC",
+ .stream_name = "DSP-CODEC",
+ .cpu_dai_name = "wm0010-sdi2",
+ .codec_name = "codec-3,
+ .codec_dai_name = "codec-3-dai_name",
+ .dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF
+ | SND_SOC_DAIFMT_CBM_CFM,
+ .ignore_suspend = 1,
+ .params = &dsp_codec_params,
+},
+
+Above code snippet is motivated from sound/soc/samsung/speyside.c.
+
+Note the "params" callback which lets the dapm know that this
+dai_link is a codec to codec connection.
+
+In dapm core a route is created between cpu_dai playback widget
+and codec_dai capture widget for playback path and vice-versa is
+true for capture path. In order for this aforementioned route to get
+triggered, DAPM needs to find a valid endpoint which could be either
+a sink or source widget corresponding to playback and capture path
+respectively.
+
+In order to trigger this dai_link widget, a thin codec driver for
+the speaker amp can be created as demonstrated in wm8727.c file, it
+sets appropriate constraints for the device even if it needs no control.
+
+Make sure to name your corresponding cpu and codec playback and capture
+dai names ending with "Playback" and "Capture" respectively as dapm core
+will link and power those dais based on the name.
+
+Note that in current device tree there is no way to mark a dai_link
+as codec to codec. However, it may change in future.