Input: Revert "Revert "synaptics - use dmax in input_mt_assign_slots""

This reverts commit 09d042a2eb90 ("Revert "Input: synaptics - use dmax in
input_mt_assign_slots"")

Now that balanced slots assignments seem to be fixed, let's re-enable the
use in synaptics.c and wait for users to complain if there are still
problems.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Henrik Rydberg <rydberg@bitmath.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/synaptics.c

@@ -67,6 +67,9 @@
 #define X_MAX_POSITIVE 8176
 #define Y_MAX_POSITIVE 8176
 
+/* maximum ABS_MT_POSITION displacement (in mm) */
+#define DMAX 10
+
 /*****************************************************************************
  *	Stuff we need even when we do not want native Synaptics support
  ****************************************************************************/
@@ -917,7 +920,7 @@ static void synaptics_report_mt_data(struct psmouse *psmouse,
 		pos[i].y = synaptics_invert_y(hw[i]->y);
 	}
 
-	input_mt_assign_slots(dev, slot, pos, nsemi, 0);
+	input_mt_assign_slots(dev, slot, pos, nsemi, DMAX * priv->x_res);
 
 	for (i = 0; i < nsemi; i++) {
 		input_mt_slot(dev, slot[i]);