From: Keith Winstein keithw@cs.stanford.edu
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 keithw@cs.stanford.edu Tested-by: Keith Winstein keithw@cs.stanford.edu Cc: stable@vger.kernel.org BugLink: https://lore.kernel.org/r/20201027071841.GA164525@trolley.csail.mit.edu Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- sound/usb/pcm.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/sound/usb/pcm.c +++ b/sound/usb/pcm.c @@ -350,6 +350,10 @@ static int set_sync_ep_implicit_fb_quirk 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;