HID: multitouch: support T and C for win8 devices

Win8 input specification clarifies the X and Y sent by devices.
It distincts the position where the user wants to Touch (T) from
the center of the ellipsoide (C). This patch enable supports for this
distinction in hid-multitouch.
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

@@ -54,7 +54,7 @@ MODULE_LICENSE("GPL");
 #define MT_QUIRK_NO_AREA		(1 << 9)
 
 struct mt_slot {
-	__s32 x, y, p, w, h;
+	__s32 x, y, cx, cy, p, w, h;
 	__s32 contactid;	/* the device ContactID assigned to this slot */
 	bool touch_state;	/* is the touch valid? */
 };
@@ -322,6 +322,7 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 	struct mt_device *td = hid_get_drvdata(hdev);
 	struct mt_class *cls = &td->mtclass;
 	int code;
+	struct hid_usage *prev_usage = NULL;
 
 	/* Only map fields from TouchScreen or TouchPad collections.
 	* We need to ignore fields that belong to other collections
@@ -344,23 +345,42 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 	if (field->physical == HID_DG_STYLUS)
 		return -1;
 
+	if (usage->usage_index)
+		prev_usage = &field->usage[usage->usage_index - 1];
+
 	switch (usage->hid & HID_USAGE_PAGE) {
 
 	case HID_UP_GENDESK:
 		switch (usage->hid) {
 		case HID_GD_X:
+			if (prev_usage && (prev_usage->hid == usage->hid)) {
+				hid_map_usage(hi, usage, bit, max,
+					EV_ABS, ABS_MT_TOOL_X);
+				set_abs(hi->input, ABS_MT_TOOL_X, field,
+					cls->sn_move);
+			} else {
 				hid_map_usage(hi, usage, bit, max,
 					EV_ABS, ABS_MT_POSITION_X);
 				set_abs(hi->input, ABS_MT_POSITION_X, field,
 					cls->sn_move);
+			}
+
 			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		case HID_GD_Y:
+			if (prev_usage && (prev_usage->hid == usage->hid)) {
+				hid_map_usage(hi, usage, bit, max,
+					EV_ABS, ABS_MT_TOOL_Y);
+				set_abs(hi->input, ABS_MT_TOOL_Y, field,
+					cls->sn_move);
+			} else {
 				hid_map_usage(hi, usage, bit, max,
 					EV_ABS, ABS_MT_POSITION_Y);
 				set_abs(hi->input, ABS_MT_POSITION_Y, field,
 					cls->sn_move);
+			}
+
 			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
@@ -501,6 +521,8 @@ static void mt_complete_slot(struct mt_device *td, struct input_dev *input)
 
 			input_event(input, EV_ABS, ABS_MT_POSITION_X, s->x);
 			input_event(input, EV_ABS, ABS_MT_POSITION_Y, s->y);
+			input_event(input, EV_ABS, ABS_MT_TOOL_X, s->cx);
+			input_event(input, EV_ABS, ABS_MT_TOOL_Y, s->cy);
 			input_event(input, EV_ABS, ABS_MT_ORIENTATION, wide);
 			input_event(input, EV_ABS, ABS_MT_PRESSURE, s->p);
 			input_event(input, EV_ABS, ABS_MT_TOUCH_MAJOR, major);
@@ -552,9 +574,15 @@ static int mt_event(struct hid_device *hid, struct hid_field *field,
 			td->curdata.p = value;
 			break;
 		case HID_GD_X:
+			if (usage->code == ABS_MT_TOOL_X)
+				td->curdata.cx = value;
+			else
 				td->curdata.x = value;
 			break;
 		case HID_GD_Y:
+			if (usage->code == ABS_MT_TOOL_Y)
+				td->curdata.cy = value;
+			else
 				td->curdata.y = value;
 			break;
 		case HID_DG_WIDTH: