From c77099bc9b725feebb94c9af25d1b1dce8659eb4 Mon Sep 17 00:00:00 2001 From: Keith Winstein Date: Sun, 25 Oct 2020 22:05:47 -0700 Subject: [PATCH] ALSA: usb-audio: Add implicit feedback quirk for Zoom UAC-2 commit f15cfca818d756dd1c9492530091dfd583359db3 upstream. The Zoom UAC-2 USB audio interface provides an async playback endpoint ("1 OUT (ASYNC)") and capture endpoint ("2 IN (ASYNC)"), both with 2-channel S32_LE in 44.1, 48, 88.2, 96, 176.4, or 192 kilosamples/s. The device provides explicit feedback to adjust the host's playback rate, but the feedback appears unstable and biased relative to the device's capture rate. "alsaloop -t 1000" experiences playback underruns and tries to resample the captured audio to match the varying playback rate. Forcing the kernel to use implicit feedback appears to produce more stable results. This causes the host to transmit one playback sample for each capture sample received. (Zoom North America has been notified of this change.) Signed-off-by: Keith Winstein Tested-by: Keith Winstein Cc: BugLink: https://lore.kernel.org/r/20201027071841.GA164525@trolley.csail.mit.edu Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/usb/pcm.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c index b401ee894e1bb..31b1edf53c417 100644 --- a/sound/usb/pcm.c +++ b/sound/usb/pcm.c @@ -352,6 +352,10 @@ static int set_sync_ep_implicit_fb_quirk(struct snd_usb_substream *subs, ep = 0x81; ifnum = 2; goto add_sync_ep_from_ifnum; + case USB_ID(0x1686, 0xf029): /* Zoom UAC-2 */ + ep = 0x82; + ifnum = 2; + goto add_sync_ep_from_ifnum; case USB_ID(0x1397, 0x0001): /* Behringer UFX1604 */ case USB_ID(0x1397, 0x0002): /* Behringer UFX1204 */ ep = 0x81;