Add KEY_MICMUTE and enable it on Lenovo X220

I suspect that this works on T410.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c
index 26c5b11..7bd829f 100644
--- a/drivers/platform/x86/thinkpad_acpi.c
+++ b/drivers/platform/x86/thinkpad_acpi.c
@@ -3186,8 +3186,17 @@
 		KEY_VENDOR,	/* 0x17: Thinkpad/AccessIBM/Lenovo */
 
 		/* (assignments unknown, please report if found) */
+		KEY_UNKNOWN, KEY_UNKNOWN,
+
+		/*
+		 * The mic mute button only sends 0x1a.  It does not
+		 * automatically mute the mic or change the mute light.
+		 */
+		KEY_MICMUTE,	/* 0x1a: Mic mute (since ?400 or so) */
+
+		/* (assignments unknown, please report if found) */
 		KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN,
-		KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN, KEY_UNKNOWN,
+		KEY_UNKNOWN,
 		},
 	};