Commit e581f1ce authored by Takashi Iwai's avatar Takashi Iwai
Browse files

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: default avatarTakashi Iwai <tiwai@suse.de>
parent 9c9a3b9d

sound/usb/pcm.c

+6 −2
Original line number Diff line number Diff line
@@ -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);