Dne 22. 12. 21 v 13:26 Pavel Hofman napsal(a):
Dne 21. 12. 21 v 13:18 John Keeping napsal(a):
On Mon, Dec 20, 2021 at 10:11:26PM +0100, Pavel Hofman wrote:
When the USB host stops capture/playback, the corresponding PCM
substream (if activated and running) is stopped and drained.
Signed-off-by: Pavel Hofman <pavel.hofman@xxxxxxxxxxx>
---
drivers/usb/gadget/function/u_audio.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/drivers/usb/gadget/function/u_audio.c
b/drivers/usb/gadget/function/u_audio.c
index a6293415c071..9dbce51c2eb7 100644
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c
@@ -544,6 +544,20 @@ static void set_reported_srate(struct
uac_rtd_params *prm, int srate)
}
}
+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))
+ snd_pcm_stop(substream, SNDRV_PCM_STATE_DRAINING);
I'm not sure if this is right (and the series should probably be CC'd to
alsa-devel to check the audio side of this).
DRAINING seems to be right for capture, but for playback should this end
up in state SETUP? Does this need to handle resuming a paused stream
like snd_pcm_drain() does?
Honestly, I do not know. This code comes from a SPDIF receiver driver
where it handles interrupted incoming SPDIF stream. You are right it is
related to capture. I will ask the alsa devs about the playback solution
specifically.
Yes I will CC the next version to alsa-dev just in case.
I have not received a response from the alsa devels yet, however based
on existing variants in the other drivers in the kernel there are two
options:
if (substream) {
snd_pcm_stream_lock_irqsave(substream, _flags);
if (snd_pcm_running(substream)) {
if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
snd_pcm_stop(substream, SNDRV_PCM_STATE_SETUP);
else
snd_pcm_stop(substream, SNDRV_PCM_STATE_DRAINING);
}
snd_pcm_stream_unlock_irqrestore(substream, _flags);
}
When testing playback/capture, sox does not exit with this version (only
reporting an error), recovering if playback/capture resume within
standard alsa blocking read/write timeout. Aplay/arecord exit.
Another option is
if (substream) {
snd_pcm_stream_lock_irqsave(substream, _flags);
if (snd_pcm_running(substream))
snd_pcm_stop(substream, SNDRV_PCM_STATE_DISCONNECTED);
snd_pcm_stream_unlock_irqrestore(substream, _flags);
}
Here both sox and aplay/arecord exit when the pcm stream is stopped.
From my use case I like this option better.
Or the gadget can use SETUP/DRAINING for host-side playback/capture stop
and DISCONNECTED for USB cable unplugging. But I am not sure whether
from the gadget side POW there is a any real difference between the host
stopping playback/capture and cable disconnection.
Also this patch would change behaviour of the gadget for existing
installations, as the existing version just stops data
delivery/consumption. Maybe some installations already count on this
behaviour. Perhaps the snd_pcm_stop call should be an opt-in via a new
configfs parameter?
Please can existing gadget users comment on this?
Thanks a lot,
Pavel.
