On 03. 01. 22 9:22, Pavel Hofman wrote:
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?
The disconnection state is unrecoverable. It's expected that the device will
be freed and cannot be reused.
If you expect to keep the PCM device, we should probably introduce a new
function which puts the device to the SNDRV_PCM_STATE_OPEN state. In this
state, all I/O routines will return -EBADFD for the applications, so they
should close or re-initialize the PCM device completely.
https://elixir.bootlin.com/linux/latest/source/sound/core/pcm_native.c#L794
Jaroslav
--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
