HID: multitouch: add support for Win 8.1 multitouch touchpads

Multitouch touchpads built for Win 8.1 need to be sent an input mode feature report
in order to start reporting multitouch events. This is the same process sent
to Win 7 multitouch touchscreens except the value of the feature report is 3 for
touchpads.

Signed-off-by: Andrew Duggan <[e-mail]>
Reviewed-by: Benjamin Tissoires <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

drivers/hid/hid-multitouch.c

···
 #define MT_QUIRK_HOVERING		(1 << 11)
 #define MT_QUIRK_CONTACT_CNT_ACCURATE	(1 << 12)
 
+#define MT_INPUTMODE_TOUCHSCREEN	0x02
+#define MT_INPUTMODE_TOUCHPAD		0x03
+
 struct mt_slot {
 	__s32 x, y, cx, cy, p, w, h;
 	__s32 contactid;	/* the device ContactID assigned to this slot */
···
 	__s16 inputmode_index;	/* InputMode HID feature index in the report */
 	__s16 maxcontact_report_id;	/* Maximum Contact Number HID feature,
 				   -1 if non-existent */
+	__u8 inputmode_value;  /* InputMode HID feature value */
 	__u8 num_received;	/* how many contacts we received */
 	__u8 num_expected;	/* expected last contact index */
 	__u8 maxcontacts;
···
 	 * Model touchscreens providing buttons as touchpads.
 	 */
 	if (field->application == HID_DG_TOUCHPAD ||
-	    (usage->hid & HID_USAGE_PAGE) == HID_UP_BUTTON)
+	    (usage->hid & HID_USAGE_PAGE) == HID_UP_BUTTON) {
 		td->mt_flags |= INPUT_MT_POINTER;
+		td->inputmode_value = MT_INPUTMODE_TOUCHPAD;
+	}
 
 	if (usage->usage_index)
 		prev_usage = &field->usage[usage->usage_index - 1];
···
 	re = &(hdev->report_enum[HID_FEATURE_REPORT]);
 	r = re->report_id_hash[td->inputmode];
 	if (r) {
-		r->field[0]->value[td->inputmode_index] = 0x02;
+		r->field[0]->value[td->inputmode_index] = td->inputmode_value;
 		hid_hw_request(hdev, r, HID_REQ_SET_REPORT);
 	}
 }
···
 	td->mtclass = *mtclass;
 	td->inputmode = -1;
 	td->maxcontact_report_id = -1;
+	td->inputmode_value = MT_INPUTMODE_TOUCHSCREEN;
 	td->cc_index = -1;
 	td->mt_report_id = -1;
 	hid_set_drvdata(hdev, td);