Merge v7.1.4linux-rolling-stable

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 6fbcb117555c..24cd7692bd01 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -1780,8 +1780,16 @@ static void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep,
 		/*
 		 * skip empty packets. At least M-Audio's Fast Track Ultra stops
 		 * streaming once it received a 0-byte OUT URB
+		 *
+		 * However, on devices where bytes==0 means every sync-source
+		 * packet errored (e.g. Behringer Flow 8 returning -EXDEV bursts
+		 * for entire capture URBs), an unconditional return starves the
+		 * IFB-fed OUT ring permanently. Such devices set
+		 * QUIRK_FLAG_IFB_SILENCE_ON_EMPTY to fall through and enqueue a
+		 * packet_info with size 0 packets, so playback emits silence
+		 * and the OUT ring keeps moving.
 		 */
-		if (bytes == 0)
+		if (bytes == 0 && !(ep->chip->quirk_flags & QUIRK_FLAG_IFB_SILENCE_ON_EMPTY))
 			return;
 
 		spin_lock_irqsave(&ep->lock, flags);