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);
