HID: multitouch: Only look at non touch fields in first packet of a frame

Devices in "single finger hybrid mode" will send one report per finger,
on some devices only the first report of such a multi-packet frame will
contain a value for BTN_LEFT, in subsequent reports (if multiple fingers
are down) the value is always 0, causing hid-mt to report BTN_LEFT going
1 - 0 - 1 - 0 when pressing a clickpad and putting down a second finger.
This happens for example on USB 0603:0002 mt touchpads.

This commit fixes this by only reporting non touch fields for the first
packet of a (possibly) multi-packet frame.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-multitouch.c

@@ -787,9 +787,11 @@ static int mt_touch_event(struct hid_device *hid, struct hid_field *field,
 }
 
 static void mt_process_mt_event(struct hid_device *hid, struct hid_field *field,
-				struct hid_usage *usage, __s32 value)
+				struct hid_usage *usage, __s32 value,
+				bool first_packet)
 {
 	struct mt_device *td = hid_get_drvdata(hid);
+	__s32 cls = td->mtclass.name;
 	__s32 quirks = td->mtclass.quirks;
 	struct input_dev *input = field->hidinput->input;
 
@@ -846,6 +848,15 @@ static void mt_process_mt_event(struct hid_device *hid, struct hid_field *field,
 			break;
 
 		default:
+			/*
+			 * For Win8 PTP touchpads we should only look at
+			 * non finger/touch events in the first_packet of
+			 * a (possible) multi-packet frame.
+			 */
+			if ((cls == MT_CLS_WIN_8 || cls == MT_CLS_WIN_8_DUAL) &&
+			    !first_packet)
+				return;
+
 			if (usage->type)
 				input_event(input, usage->type, usage->code,
 						value);
@@ -866,6 +877,7 @@ static void mt_touch_report(struct hid_device *hid, struct hid_report *report)
 	struct mt_device *td = hid_get_drvdata(hid);
 	__s32 cls = td->mtclass.name;
 	struct hid_field *field;
+	bool first_packet;
 	unsigned count;
 	int r, n, scantime = 0;
 
@@ -901,6 +913,7 @@ static void mt_touch_report(struct hid_device *hid, struct hid_report *report)
 	}
 	td->prev_scantime = scantime;
 
+	first_packet = td->num_received == 0;
 	for (r = 0; r < report->maxfield; r++) {
 		field = report->field[r];
 		count = field->report_count;
@@ -910,7 +923,7 @@ static void mt_touch_report(struct hid_device *hid, struct hid_report *report)
 
 		for (n = 0; n < count; n++)
 			mt_process_mt_event(hid, field, &field->usage[n],
-					field->value[n]);
+					    field->value[n], first_packet);
 	}
 
 	if (td->num_received >= td->num_expected)