HID: wacom: generic: only switch the mode on devices with LEDs

Currently, the driver will attempt to set the mode on all
devices with a center button, but some devices with a center
button lack LEDs, and attempting to set the LEDs on devices
without LEDs results in the kernel error message of the form:

"leds input8::wacom-0.1: Setting an LED's brightness failed (-32)"

This is because the generic codepath erroneously assumes that the
BUTTON_CENTER usage indicates that the device has LEDs, the
previously ignored TOUCH_RING_SETTING usage is a more accurate
indication of the existence of LEDs on the device.

Fixes: 10c55cac ("HID: wacom: generic: support LEDs")
Cc: <stable@vger.kernel.org> # v4.11+
Signed-off-by: Aaron Armstrong Skomra <aaron.skomra@wacom.com>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_sys.c

@@ -307,6 +307,9 @@ static void wacom_feature_mapping(struct hid_device *hdev,
 	wacom_hid_usage_quirk(hdev, field, usage);
 
 	switch (equivalent_usage) {
+	case WACOM_HID_WD_TOUCH_RING_SETTING:
+		wacom->generic_has_leds = true;
+		break;
 	case HID_DG_CONTACTMAX:
 		/* leave touch_max as is if predefined */
 		if (!features->touch_max) {

drivers/hid/wacom_wac.c

@@ -1906,8 +1906,6 @@ static void wacom_wac_pad_usage_mapping(struct hid_device *hdev,
 		features->device_type |= WACOM_DEVICETYPE_PAD;
 		break;
 	case WACOM_HID_WD_BUTTONCENTER:
-		wacom->generic_has_leds = true;
-		/* fall through */
 	case WACOM_HID_WD_BUTTONHOME:
 	case WACOM_HID_WD_BUTTONUP:
 	case WACOM_HID_WD_BUTTONDOWN:

drivers/hid/wacom_wac.h

@@ -145,6 +145,7 @@
 #define WACOM_HID_WD_OFFSETBOTTOM       (WACOM_HID_UP_WACOMDIGITIZER | 0x0d33)
 #define WACOM_HID_WD_DATAMODE           (WACOM_HID_UP_WACOMDIGITIZER | 0x1002)
 #define WACOM_HID_WD_DIGITIZERINFO      (WACOM_HID_UP_WACOMDIGITIZER | 0x1013)
+#define WACOM_HID_WD_TOUCH_RING_SETTING (WACOM_HID_UP_WACOMDIGITIZER | 0x1032)
 #define WACOM_HID_UP_G9                 0xff090000
 #define WACOM_HID_G9_PEN                (WACOM_HID_UP_G9 | 0x02)
 #define WACOM_HID_G9_TOUCHSCREEN        (WACOM_HID_UP_G9 | 0x11)