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

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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: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2021-09-29 10:08:40 +02:00
parent e581f1cec4
commit bceee75387
1 changed files with 3 additions and 0 deletions
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3
sound/usb/pcm.c
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@ -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;