[PATCH] ALSA: usb-audio: work around KEF X300A firmware bug

[Clemens Ladisch <clemens@ladisch.de>]

When the driver tries to access Function Unit 10, the KEF X300A
speakers' firmware apparently locks up, making even PCM streaming
impossible.  Work around this by ignoring this FU.

Cc: <stable@vger.kernel.org>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
---
 sound/usb/mixer_maps.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/sound/usb/mixer_maps.c b/sound/usb/mixer_maps.c
index 32af6b7..d1d72ff 100644
--- a/sound/usb/mixer_maps.c
+++ b/sound/usb/mixer_maps.c
@@ -328,6 +328,11 @@ static struct usbmix_name_map gamecom780_map[] = {
 	{}
 };

+static const struct usbmix_name_map kef_x300a_map[] = {
+	{ 10, NULL }, /* firmware locks up (?) when we try to access this FU */
+	{ 0 }
+};
+
 /*
  * Control map entries
  */
@@ -419,6 +424,10 @@ static struct usbmix_ctl_map usbmix_ctl_maps[] = {
 		.id = USB_ID(0x200c, 0x1018),
 		.map = ebox44_map,
 	},
+	{
+		.id = USB_ID(0x27ac, 0x1000),
+		.map = kef_x300a_map,
+	},
 	{ 0 } /* terminator */
 };