touchpad: use the fuzz value (if any) for the hysteresis margin

We currently used 0.5mm on touchpads as hysteresis value. This causes pointer
movement delays, it is likely too high. Reduce it to a kernel-set fuzz value
(if any) and see how we go with that. On many touchpads, the fuzz is 8 which
would be closer to 0.2mm on e.g. a T440.

Note that the does some defuzzing anyway, but the response of that function is
nonlinear, e.g. for a fuzz of 8, the physical deltas map to:

phys 0..3  → delta 0
phys 4..7  → delta 1
phys 8..15 → delta 4, 5, 6, 7
phys 16..N → delta 16..N

In other words, we never see some logical deltas 2 and 3. While this shouldn't
matter given the average touchpad resolution, reducing the hysteresis margin
is likely to provide some better response. We never see values 8-15 either
which could be the cause of some pointer jumps we've been seeing.

see https://bugs.freedesktop.org/show_bug.cgi?id=105303

Devices with a fuzz of 0 have the hysteresis margin reduced to 0.25mm (from
0.5mm).

https://bugs.freedesktop.org/show_bug.cgi?id=105108

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit ea7498ef971350454db9c78b9ba160e7d6bb455b)

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index d6e1e4f97806c13156b345765b17dc128e74d60d..8a3923c73cd9d4e16d56a8e4a3fb99024c3c7ede 100644 (file)
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -3026,12 +3026,22 @@ tp_init_default_resolution(struct tp_dispatch *tp,
 static inline void
 tp_init_hysteresis(struct tp_dispatch *tp)
 {
-       int res_x, res_y;
+       int xmargin, ymargin;
+       const struct input_absinfo *ax = tp->device->abs.absinfo_x,
+                                  *ay = tp->device->abs.absinfo_y;
 
-       res_x = tp->device->abs.absinfo_x->resolution;
-       res_y = tp->device->abs.absinfo_y->resolution;
-       tp->hysteresis.margin.x = res_x/2;
-       tp->hysteresis.margin.y = res_y/2;
+       if (ax->fuzz)
+               xmargin = ax->fuzz;
+       else
+               xmargin = ax->resolution/4;
+
+       if (ay->fuzz)
+               ymargin = ay->fuzz;
+       else
+               ymargin = ay->resolution/4;
+
+       tp->hysteresis.margin.x = xmargin;
+       tp->hysteresis.margin.y = ymargin;
        tp->hysteresis.enabled = false;
 }