From e581f1cec4f899f788f6c9477f805b1d5fef25e2 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Wed, 29 Sep 2021 10:08:39 +0200
Subject: [PATCH] ALSA: usb-audio: Disable low-latency playback for free-wheel mode
Git-commit: e581f1cec4f899f788f6c9477f805b1d5fef25e2
Patch-mainline: v5.16-rc1
References: bsc#1192354
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@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
sound/usb/pcm.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 4dd7f1c9e2af..84b03a32ee23 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -582,7 +582,8 @@ static int snd_usb_hw_free(struct snd_pcm_substream *substream)
}
/* 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(struct snd_usb_substream *subs)
/* 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 snd_pcm_substream *substream)
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);
--
2.26.2