HID: multitouch: fix Win 8 protocol

The Win 8 protocol specify the fact that each valid touch must be reported
within a frame until it is released.
We can therefore use the always_valid quirk and dismiss reports when we see
duplicate contacts ID.

We recognize Win8 certified devices from their vendor feature 0xff0000c5
where Microsoft put a signed blob in the report to check if the device
passed the certification.
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

@@ -294,6 +294,18 @@ static void mt_feature_mapping(struct hid_device *hdev,
 			td->maxcontacts = td->mtclass.maxcontacts;
 
 		break;
+	case 0xff0000c5:
+		if (field->report_count == 256 && field->report_size == 8) {
+			/* Win 8 devices need special quirks */
+			__s32 *quirks = &td->mtclass.quirks;
+			*quirks |= MT_QUIRK_ALWAYS_VALID;
+			*quirks |= MT_QUIRK_IGNORE_DUPLICATES;
+			*quirks |= MT_QUIRK_HOVERING;
+			*quirks &= ~MT_QUIRK_NOT_SEEN_MEANS_UP;
+			*quirks &= ~MT_QUIRK_VALID_IS_INRANGE;
+			*quirks &= ~MT_QUIRK_VALID_IS_CONFIDENCE;
+		}
+		break;
 	}
 }