This is a note to let you know that I've just added the patch titled
ALSA: usb-audio: Disable low-latency playback for free-wheel mode
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
alsa-usb-audio-disable-low-latency-playback-for-free-wheel-mode.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e581f1cec4f899f788f6c9477f805b1d5fef25e2 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@xxxxxxx>
Date: Wed, 29 Sep 2021 10:08:39 +0200
Subject: ALSA: usb-audio: Disable low-latency playback for free-wheel mode
From: Takashi Iwai <tiwai@xxxxxxx>
commit e581f1cec4f899f788f6c9477f805b1d5fef25e2 upstream.
The free-wheel stream operation like dmix may not update the appl_ptr
appropriately, and it doesn't fit with the low-latency playback mode.
Disable the low-latency playback operation when the stream is set up
in such a mode.
Link: https://lore.kernel.org/r/20210929080844.11583-5-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
sound/usb/pcm.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -582,7 +582,8 @@ static int snd_usb_hw_free(struct snd_pc
}
/* check whether early start is needed for playback stream */
-static int lowlatency_playback_available(struct snd_usb_substream *subs)
+static int lowlatency_playback_available(struct snd_pcm_runtime *runtime,
+ struct snd_usb_substream *subs)
{
struct snd_usb_audio *chip = subs->stream->chip;
@@ -591,6 +592,9 @@ static int lowlatency_playback_available
/* disabled via module option? */
if (!chip->lowlatency)
return false;
+ /* free-wheeling mode? (e.g. dmix) */
+ if (runtime->stop_threshold > runtime->buffer_size)
+ return false;
/* too short periods? */
if (subs->data_endpoint->nominal_queue_size >= subs->buffer_bytes)
return false;
@@ -630,7 +634,7 @@ static int snd_usb_pcm_prepare(struct sn
subs->period_elapsed_pending = 0;
runtime->delay = 0;
- subs->lowlatency_playback = lowlatency_playback_available(subs);
+ subs->lowlatency_playback = lowlatency_playback_available(runtime, subs);
if (!subs->lowlatency_playback)
ret = start_endpoints(subs);
Patches currently in stable-queue which might be from tiwai@xxxxxxx are
queue-5.15/alsa-usb-audio-rename-early_playback_start-flag-with-lowlatency_playback.patch
queue-5.15/alsa-usb-audio-disable-low-latency-playback-for-free-wheel-mode.patch
queue-5.15/alsa-usb-audio-avoid-killing-in-flight-urbs-during-draining.patch
queue-5.15/alsa-usb-audio-less-restriction-for-low-latency-playback-mode.patch
queue-5.15/alsa-usb-audio-improved-lowlatency-playback-support.patch
queue-5.15/alsa-usb-audio-check-available-frames-for-the-next-packet-size.patch
queue-5.15/alsa-usb-audio-switch-back-to-non-latency-mode-at-a-later-point.patch
queue-5.15/alsa-usb-audio-fix-packet-size-calculation-regression.patch
queue-5.15/alsa-usb-audio-don-t-start-stream-for-capture-at-prepare.patch
queue-5.15/alsa-usb-audio-disable-low-latency-mode-for-implicit-feedback-sync.patch
queue-5.15/alsa-usb-audio-add-spinlock-to-stop_urbs.patch
queue-5.15/alsa-usb-audio-restrict-rates-for-the-shared-clocks.patch
