Commit bceee753 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: usb-audio: Disable low-latency mode for implicit feedback sync 

When a playback stream runs in the implicit feedback mode, its
operation is passive and won't start unless the capture packet is
received.  This behavior contradicts with the low-latency playback
mode, and we should turn off lowlatency_playback flag accordingly.

In theory, we may take the low-latency mode when the playback-first
quirk is set, but it still conflicts with the later operation with the
fixed packet numbers, so it's disabled all together for now.

Link: https://lore.kernel.org/r/20210929080844.11583-6-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent e581f1ce

sound/usb/pcm.c

+3 −0
Original line number Diff line number Diff line
@@ -595,6 +595,9 @@ static int lowlatency_playback_available(struct snd_pcm_runtime *runtime, 
	/* free-wheeling mode? (e.g. dmix) */

	if (runtime->stop_threshold > runtime->buffer_size)

		return false;

	/* implicit feedback mode has own operation mode */

	if (snd_usb_endpoint_implicit_feedback_sink(subs->data_endpoint))

		return false;

	/* too short periods? */

	if (subs->data_endpoint->nominal_queue_size >= subs->buffer_bytes)

		return false;