[alsa-devel] ASoC Multiple outputs

[Liam Girdwood]

Reflowed formatting. Best to always CC maintainers too.

On Mon, 2015-07-13 at 07:39 +0000, Matt Redfearn wrote:
> Hi list,
> I am writing an ALSA driver for an SoC / board which has a single I2S
> source. The source may be connected internally to either a codec
> outputting to analogue headphones, or to an HDMI transmitter.
> At the moment I have set up two snd_soc_dai_link within the same card
> connecting the source to each sink. 
> 
> static struct snd_soc_dai_link ci20_dai_link[] = {
> 	{
> 		.name = "ci20",
> 		.stream_name = "headphones",
> 		.cpu_dai_name = "jz4780-i2s",
> 		.platform_name = "jz4780-i2s",
> 		.codec_dai_name = "jz4780-hifi",
> 		.codec_name = "jz4780-codec",
> 		.init = ci20_init,
> 		.ops = &ci20_audio_dai_ops,
> 		.dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF | SND_SOC_DAIFMT_CBM_CFM,
> 	},
> 	{
> 		.name = "ci20 HDMI",
> 		.stream_name = "hdmi",
> 		.cpu_dai_name = "jz4780-i2s",
> 		.platform_name = "jz4780-i2s",
> 		.codec_dai_name = "dw-hdmi-hifi",
> 		.codec_name = "dw-hdmi-audio",
> 		.init = ci20_hdmi_init,
> 		.ops = &ci20_audio_dai_ops,
> 		.dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF | SND_SOC_DAIFMT_CBS_CFS,
> 	}
> };
> 
> This works and creates 2 devices, and I am able to get mplayer to play
> sound out to either the headphones or HDMI using the argument "-ao
> alsa:device=hw=0.0" or "-ao alsa:device=hw=0.1"
> 
> aplay -l
> **** List of PLAYBACK Hardware Devices ****
> card 0: ci20 [ci20], device 0: headphones jz4780-hifi-0 []
>   Subdevices: 1/1
>   Subdevice #0: subdevice #0
> card 0: ci20 [ci20], device 1: hdmi jz4780-hdmi-hifi-1 []
>   Subdevices: 1/1
>   Subdevice #0: subdevice #0
> 
> However, alsamixer does not show anything about the second device
> (HDMI), only the analogue output associated with device 0.


> Please could someone advise what is the "correct" way to set up
> multiple links in such a system such that the headphones / HDMI
> outputs appear in the mixer and are available to pulseaudio.

This looks correct. You have a PCM for each device.  The mixers should
all be available for both PCMs unless there are mixer naming
problems/collisions ?

>  Should I create multiple cards? Should I create subdevices for the
> different outputs? If so, what structures should be set up within the
> driver to achieve this?
> Suggestions of any documentation / websites that may help would be
> great!

Best to use a single card if the audio HW is shared between HDMI and
analog otherwise you could create separate cards if no audio HW is
shared between either PCM.

Liam

> 
> Thanks!
> Matt
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