HID: multitouch: add MT_QUIRK_IGNORE_DUPLICATES

This quirk allows a device to reuse a contact id when sending garbage
inactive contacts at the end of a report.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-multitouch.c

@@ -52,6 +52,7 @@ MODULE_LICENSE("GPL");
 #define MT_QUIRK_VALID_IS_CONFIDENCE	(1 << 6)
 #define MT_QUIRK_SLOT_IS_CONTACTID_MINUS_ONE	(1 << 8)
 #define MT_QUIRK_NO_AREA		(1 << 9)
+#define MT_QUIRK_IGNORE_DUPLICATES	(1 << 10)
 
 struct mt_slot {
 	__s32 x, y, cx, cy, p, w, h;
@@ -505,10 +506,18 @@ static void mt_complete_slot(struct mt_device *td, struct input_dev *input)
 	if (td->curvalid || (td->mtclass.quirks & MT_QUIRK_ALWAYS_VALID)) {
 		int slotnum = mt_compute_slot(td, input);
 		struct mt_slot *s = &td->curdata;
+		struct input_mt *mt = input->mt;
 
 		if (slotnum < 0 || slotnum >= td->maxcontacts)
 			return;
 
+		if ((td->mtclass.quirks & MT_QUIRK_IGNORE_DUPLICATES) && mt) {
+			struct input_mt_slot *slot = &mt->slots[slotnum];
+			if (input_mt_is_active(slot) &&
+			    input_mt_is_used(mt, slot))
+				return;
+		}
+
 		input_mt_slot(input, slotnum);
 		input_mt_report_slot_state(input, MT_TOOL_FINGER,
 			s->touch_state);