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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.
- A dai_link in a "simple-audio-card" will automatically be detected as
- codec to codec when all DAIs on the link belong to codec components.
- The dai_link will be initialized with the subset of stream parameters
- (channels, format, sample rate) supported by all DAIs on the link. Since
- there is no way to provide these parameters in the device tree, this is
- mostly useful for communication with simple fixed-function codecs, such
- as a Bluetooth controller or cellular modem.
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