Commit 53451b6d authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: usb-audio: Less restriction for low-latency playback mode 

The recent support for the improved low-latency playback mode applied
the SNDRV_PCM_INFO_EXPLICIT_SYNC flag for the target streams, but this
was a slight overkill.  The use of the flag above disables effectively
both PCM status and control mmaps, while basically what we want to
track is only about the appl_ptr update.

For less restriction, use a more proper flag,
SNDRV_PCM_INFO_SYNC_APPLPTR instead, which disables only the control
mmap.

Fixes: d5f871f8 ("ALSA: usb-audio: Improved lowlatency playback support")
Link: https://lore.kernel.org/r/20211011103650.10182-1-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 6d277881

sound/usb/pcm.c

+1 −1
Original line number Diff line number Diff line
@@ -1102,7 +1102,7 @@ static int snd_usb_pcm_open(struct snd_pcm_substream *substream) 
	/* need an explicit sync to catch applptr update in low-latency mode */

	if (direction == SNDRV_PCM_STREAM_PLAYBACK &&

	    as->chip->lowlatency)

		runtime->hw.info |= SNDRV_PCM_INFO_EXPLICIT_SYNC;

		runtime->hw.info |= SNDRV_PCM_INFO_SYNC_APPLPTR;

	runtime->private_data = subs;

	subs->pcm_substream = substream;

	/* runtime PM is also done there */