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

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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>
This commit is contained in:
Peter Hutterer 2018-02-21 13:41:31 +10:00
parent 50418a0153
commit ea7498ef97
1 changed files with 15 additions and 5 deletions
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20
src/evdev-mt-touchpad.c
View file

@ -3093,12 +3093,22 @@ 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;
}