HID: lenovo: Detect quirk-free fw on cptkbd and stop applying workaround

Built-in firmware of cptkbd handles scrolling by itself (when middle
button is pressed) but with issues: it does not support horizontal and
hi-res scrolling and upon middle button release it sends middle button
click even if there was a scrolling event. Commit 3cb5ff02 ("HID:
lenovo: Hide middle-button press until release") workarounds last
issue but it's impossible to workaround scrolling-related issues
without firmware modification.

Likely, Dennis Schneider has reverse engineered the firmware and
provided an instruction on how to patch it [1]. However,
aforementioned workaround prevents userspace (libinput) from knowing
exact moment when middle button has been pressed down and performing
"On-Button scrolling". This commit detects correctly-behaving patched
firmware if cursor movement events has been received during middle
button being pressed and stops applying workaround for this device.

Link: https://hohlerde.org/rauch/en/elektronik/projekte/tpkbd-fix/ [1]
Signed-off-by: Mikhail Khvainitski <me@khvoinitsky.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-lenovo.c

@@ -51,7 +51,12 @@ struct lenovo_drvdata {
 	int select_right;
 	int sensitivity;
 	int press_speed;
-	u8 middlebutton_state; /* 0:Up, 1:Down (undecided), 2:Scrolling */
+	/* 0: Up
+	 * 1: Down (undecided)
+	 * 2: Scrolling
+	 * 3: Patched firmware, disable workaround
+	 */
+	u8 middlebutton_state;
 	bool fn_lock;
 };
 
@@ -668,31 +673,48 @@ static int lenovo_event_cptkbd(struct hid_device *hdev,
 {
 	struct lenovo_drvdata *cptkbd_data = hid_get_drvdata(hdev);
 
-	/* "wheel" scroll events */
-	if (usage->type == EV_REL && (usage->code == REL_WHEEL ||
-			usage->code == REL_HWHEEL)) {
-		/* Scroll events disable middle-click event */
-		cptkbd_data->middlebutton_state = 2;
-		return 0;
-	}
+	if (cptkbd_data->middlebutton_state != 3) {
+		/* REL_X and REL_Y events during middle button pressed
+		 * are only possible on patched, bug-free firmware
+		 * so set middlebutton_state to 3
+		 * to never apply workaround anymore
+		 */
+		if (cptkbd_data->middlebutton_state == 1 &&
+				usage->type == EV_REL &&
+				(usage->code == REL_X || usage->code == REL_Y)) {
+			cptkbd_data->middlebutton_state = 3;
+			/* send middle button press which was hold before */
+			input_event(field->hidinput->input,
+				EV_KEY, BTN_MIDDLE, 1);
+			input_sync(field->hidinput->input);
+		}
 
-	/* Middle click events */
-	if (usage->type == EV_KEY && usage->code == BTN_MIDDLE) {
-		if (value == 1) {
-			cptkbd_data->middlebutton_state = 1;
-		} else if (value == 0) {
-			if (cptkbd_data->middlebutton_state == 1) {
-				/* No scrolling inbetween, send middle-click */
-				input_event(field->hidinput->input,
-					EV_KEY, BTN_MIDDLE, 1);
-				input_sync(field->hidinput->input);
-				input_event(field->hidinput->input,
-					EV_KEY, BTN_MIDDLE, 0);
-				input_sync(field->hidinput->input);
+		/* "wheel" scroll events */
+		if (usage->type == EV_REL && (usage->code == REL_WHEEL ||
+				usage->code == REL_HWHEEL)) {
+			/* Scroll events disable middle-click event */
+			cptkbd_data->middlebutton_state = 2;
+			return 0;
+		}
+
+		/* Middle click events */
+		if (usage->type == EV_KEY && usage->code == BTN_MIDDLE) {
+			if (value == 1) {
+				cptkbd_data->middlebutton_state = 1;
+			} else if (value == 0) {
+				if (cptkbd_data->middlebutton_state == 1) {
+					/* No scrolling inbetween, send middle-click */
+					input_event(field->hidinput->input,
+						EV_KEY, BTN_MIDDLE, 1);
+					input_sync(field->hidinput->input);
+					input_event(field->hidinput->input,
+						EV_KEY, BTN_MIDDLE, 0);
+					input_sync(field->hidinput->input);
+				}
+				cptkbd_data->middlebutton_state = 0;
 			}
-			cptkbd_data->middlebutton_state = 0;
+			return 1;
 		}
-		return 1;
 	}
 
 	if (usage->type == EV_KEY && usage->code == KEY_FN_ESC && value == 1) {