[PATCH 5.15 010/207] ALSA: usb-audio: Less restriction for low-latency playback mode

Greg Kroah-Hartman
2021-12-06T15:35:12Z

From: Takashi Iwai <tiwai@suse.de>

commit 53451b6da8271905941eb1eb369db152c4bd92f2 upstream.

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: d5f871f89e21 ("ALSA: usb-audio: Improved lowlatency playback support")
Link: https://lore.kernel.org/r/20211011103650.10182-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/usb/pcm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1095,7 +1095,7 @@ static int snd_usb_pcm_open(struct snd_p
/* 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 */