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

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Date:   Mon,  6 Dec 2021 15:54:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Takashi Iwai <tiwai@...e.de>
Subject: [PATCH 5.15 010/207] ALSA: usb-audio: Less restriction for low-latency playback mode

From: Takashi Iwai <tiwai@...e.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@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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 */