touchpad: reduce minimum height for horiz edge scrolling to 40mm

Introduced in commit 8e7f99c27a we only allowed horizontal edge scrolling
on devices larger than 50mm to leave enough reactive space on the touchpad.
Looking at a ruler, a 50mm high touchpad is still large enough to leave the
bottom 7mm as an horizontal edge scroll area. Reduce the minimum size to 40mm
instead, that's closer to where it starts to get a bit iffy.

https://bugzilla.redhat.com/show_bug.cgi?id=1422221

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
(cherry picked from commit d6379bc3f3)

src/evdev-mt-touchpad-edge-scroll.c

@@ -291,14 +291,14 @@ tp_edge_scroll_init(struct tp_dispatch *tp, struct evdev_device *device)
 	struct phys_coords mm = { 0.0, 0.0 };
 
 	evdev_device_get_size(device, &width, &height);
-	/* Touchpads smaller than 50mm are not tall enough to have a
+	/* Touchpads smaller than 40mm are not tall enough to have a
 	   horizontal scroll area, it takes too much space away. But
 	   clickpads have enough space here anyway because of the
 	   software button area (and all these tiny clickpads were built
 	   when software buttons were a thing, e.g. Lenovo *20 series)
 	 */
 	if (!tp->buttons.is_clickpad)
-	    want_horiz_scroll = (height >= 50);
+	    want_horiz_scroll = (height >= 40);
 
 	/* 7mm edge size */
 	mm.x = width - 7;

test/test-touchpad.c

@@ -462,7 +462,7 @@ touchpad_has_horiz_edge_scroll_size(struct litest_device *dev)
 
 	rc = libinput_device_get_size(dev->libinput_device, &width, &height);
 
-	return rc == 0 && height >= 50;
+	return rc == 0 && height >= 40;
 }
 
 START_TEST(touchpad_edge_scroll_horiz)