Dne 03. 01. 22 v 10:10 Jaroslav Kysela napsal(a):
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
The fact is that after closing the USB host can re-open the device with
different samplerate (and perhaps later on with different channels
count/sample size). That would hint at the need to re-initialize the
gadget side before opening anyway.
As of keeping the device - it's likely some use cases would prefer
keeping the device, to minimize the operations needed to react to the
host-side playback/capture start.
A function you describe would make sense for this. IMO from the gadget
POW there is no difference between the host stopping playback/capture
and cable disconnection, in both cases the data stream is stopped and
next stream can have entirely different parameters. Maybe the gadget
configfs parameter could only toggle between no action (i.e. current
situation) and the new alsa function stopping the stream.
Jaroslav, please can you draft such a function? Perhaps both changes
could make it to 5.17.
Thanks a lot,
Pavel.
