HID: multitouch: Get the contact ID from HID_DG_TRANSDUCER_INDEX fields in case of Apple Touch Bar

In Apple Touch Bar, the contact ID is contained in fields with the
HID_DG_TRANSDUCER_INDEX usage rather than HID_DG_CONTACTID, thus differing
from the HID spec. Add a quirk for the same.

Acked-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Kerem Karabay <kekrby@gmail.com>
Co-developed-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

Author: kekrby

drivers/hid/hid-multitouch.c

@@ -73,6 +73,7 @@ MODULE_LICENSE("GPL");
 #define MT_QUIRK_FORCE_MULTI_INPUT	BIT(20)
 #define MT_QUIRK_DISABLE_WAKEUP		BIT(21)
 #define MT_QUIRK_ORIENTATION_INVERT	BIT(22)
+#define MT_QUIRK_APPLE_TOUCHBAR		BIT(23)
 
 #define MT_INPUTMODE_TOUCHSCREEN	0x02
 #define MT_INPUTMODE_TOUCHPAD		0x03
@@ -625,6 +626,7 @@ static struct mt_application *mt_find_application(struct mt_device *td,
 static struct mt_report_data *mt_allocate_report_data(struct mt_device *td,
 						      struct hid_report *report)
 {
+	struct mt_class *cls = &td->mtclass;
 	struct mt_report_data *rdata;
 	struct hid_field *field;
 	int r, n;
@@ -649,7 +651,11 @@ static struct mt_report_data *mt_allocate_report_data(struct mt_device *td,
 
 		if (field->logical == HID_DG_FINGER || td->hdev->group != HID_GROUP_MULTITOUCH_WIN_8) {
 			for (n = 0; n < field->report_count; n++) {
-				if (field->usage[n].hid == HID_DG_CONTACTID) {
+				unsigned int hid = field->usage[n].hid;
+
+				if (hid == HID_DG_CONTACTID ||
+				   (cls->quirks & MT_QUIRK_APPLE_TOUCHBAR &&
+				   hid == HID_DG_TRANSDUCER_INDEX)) {
 					rdata->is_mt_collection = true;
 					break;
 				}
@@ -827,6 +833,14 @@ static int mt_touch_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 						     EV_KEY, BTN_TOUCH);
 			MT_STORE_FIELD(tip_state);
 			return 1;
+		case HID_DG_TRANSDUCER_INDEX:
+			/*
+			 * Contact ID in case of Apple Touch Bars is contained
+			 * in fields with HID_DG_TRANSDUCER_INDEX usage.
+			 */
+			if (!(cls->quirks & MT_QUIRK_APPLE_TOUCHBAR))
+				return 0;
+			fallthrough;
 		case HID_DG_CONTACTID:
 			MT_STORE_FIELD(contactid);
 			app->touches_by_report++;