Input: MT - add support for balanced slot assignment

Some devices are not fast enough to differentiate between a fast-moving
contact and a new contact. This problem cannot be fully resolved because
information is truly missing, but it is possible to safe-guard against
obvious mistakes by restricting movement with a maximum displacement.

The new problem formulation for dmax > 0 cannot benefit from the speedup
for positive definite matrices, but since the convergence is faster, the
result is about the same. For a handful of contacts, the latency difference
is truly negligible.

Suggested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/alps.c

@@ -435,7 +435,7 @@ static void alps_report_mt_data(struct psmouse *psmouse, int n)
 	struct alps_fields *f = &priv->f;
 	int i, slot[MAX_TOUCHES];
 
-	input_mt_assign_slots(dev, slot, f->mt, n);
+	input_mt_assign_slots(dev, slot, f->mt, n, 0);
 	for (i = 0; i < n; i++)
 		alps_set_slot(dev, slot[i], f->mt[i].x, f->mt[i].y);
 

drivers/input/mouse/bcm5974.c

@@ -564,7 +564,7 @@ static int report_tp_state(struct bcm5974 *dev, int size)
 		dev->index[n++] = &f[i];
 	}
 
-	input_mt_assign_slots(input, dev->slots, dev->pos, n);
+	input_mt_assign_slots(input, dev->slots, dev->pos, n, 0);
 
 	for (i = 0; i < n; i++)
 		report_finger_data(input, dev->slots[i],

drivers/input/mouse/cypress_ps2.c

@@ -538,7 +538,7 @@ static void cypress_process_packet(struct psmouse *psmouse, bool zero_pkt)
 		pos[i].y = contact->y;
 	}
 
-	input_mt_assign_slots(input, slots, pos, n);
+	input_mt_assign_slots(input, slots, pos, n, 0);
 
 	for (i = 0; i < n; i++) {
 		contact = &report_data.contacts[i];

drivers/input/mouse/synaptics.c

@@ -809,7 +809,7 @@ 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);
+	input_mt_assign_slots(dev, slot, pos, nsemi, 0);
 
 	for (i = 0; i < nsemi; i++) {
 		input_mt_slot(dev, slot[i]);