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ALSA: usb-audio: Disable low-latency playback for free-wheel mode 

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>
This commit is contained in:
Takashi Iwai 2021-09-29 10:08:39 +02:00
parent 9c9a3b9da8
commit e581f1cec4
1 changed files with 6 additions and 2 deletions
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8
sound/usb/pcm.c
View File

@ -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);