Correct stopping capture and playback substreams?

[Pavel Hofman]

Dne 23. 12. 21 v 9:18 Pavel Hofman napsal(a):
> Hi Takashi,
> 
> I am working on stopping alsa streams of audio USB gadget when USB host 
> stops capture/playback/USB cable unplugged.
> 
> For capture I used code from AK4114 SPDIF receiver 
> https://elixir.bootlin.com/linux/latest/source/sound/i2c/other/ak4114.c#L590: 
> 
> 
> static void stop_substream(struct uac_rtd_params *prm)
> {
>      unsigned long _flags;
>      struct snd_pcm_substream *substream;
> 
>      substream = prm->ss;
>      if (substream) {
>          snd_pcm_stream_lock_irqsave(substream, _flags);
>          if (snd_pcm_running(substream))
>              // TODO - correct handling for playback substream?
>              snd_pcm_stop(substream, SNDRV_PCM_STATE_DRAINING);
>          snd_pcm_stream_unlock_irqrestore(substream, _flags);
>      }
> }
> 
> For setup I found calling snd_pcm_stop(substream, SNDRV_PCM_STATE_SETUP) 
> (https://elixir.bootlin.com/linux/latest/source/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c#L63) 
>   Or for both capture and playback using SNDRV_PCM_STATE_DISCONNECTED 
> (https://elixir.bootlin.com/linux/latest/source/sound/core/pcm.c#L1103).
> 
> Or perhaps using snd_pcm_dev_disconnect(dev) or snd_pcm_drop(substream)?
> 
> Please what is the recommended way?
> 

Please can I ask for expert view on this issue? E.g. in SoX stopping the 
stream with SNDRV_PCM_STATE_SETUP/SNDRV_PCM_STATE_DRAINING does not stop 
the application, while with SNDRV_PCM_STATE_DISCONNECTED SoX exits with 
non-recoverable status. I am considering implementing both methods and 
letting users choose their suitable snd_pcm_stop operation (none 
(default)/SETUP-DRAINING/DISCONNECTED) for the two events (host 
playback/capture stop, cable disconnection) with a configfs param. Would 
this make sense?

Thanks a lot in advance,

Pavel.