ALSA: usb-audio: extend KEF X300A FU 10 tweak to Arcam rPAC

commit d70a1b98 upstream.

The Arcam rPAC seems to have the same problem - whenever anything
(alsamixer, udevd, 3.9+ kernel from 60af3d03, ..) attempts to
access mixer / control interface of the card, the firmware "locks up"
the entire device, resulting in
  SNDRV_PCM_IOCTL_HW_PARAMS failed (-5): Input/output error
from alsa-lib.

Other operating systems can somehow read the mixer (there seems to be
playback volume/mute), but any manipulation is ignored by the device
(which has hardware volume controls).
Signed-off-by: Jiri Jaburek <jjaburek@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

sound/usb/mixer_maps.c

@@ -304,8 +304,11 @@ static struct usbmix_name_map hercules_usb51_map[] = {
 	{ 0 }				/* terminator */
 };
 
-static const struct usbmix_name_map kef_x300a_map[] = {
-	{ 10, NULL }, /* firmware locks up (?) when we try to access this FU */
+/* some (all?) SCMS USB3318 devices are affected by a firmware lock up
+ * when anything attempts to access FU 10 (control)
+ */
+static const struct usbmix_name_map scms_usb3318_map[] = {
+	{ 10, NULL },
 	{ 0 }
 };
 
@@ -377,8 +380,14 @@ static struct usbmix_ctl_map usbmix_ctl_maps[] = {
 		.ignore_ctl_error = 1,
 	},
 	{
+		/* KEF X300A */
 		.id = USB_ID(0x27ac, 0x1000),
-		.map = kef_x300a_map,
+		.map = scms_usb3318_map,
+	},
+	{
+		/* Arcam rPAC */
+		.id = USB_ID(0x25c4, 0x0003),
+		.map = scms_usb3318_map,
 	},
 	{ 0 } /* terminator */
 };