evdev: Query mouse DPI from udev

Instead of using a hard coded mouse DPI value, we query it from udev.
If it's not present or the property is obviously broken we fall back
to default.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
filter: fix a comment, 400 isn't hard-coded anymore

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Move DEFAULT_MOUSE_DPI to filter.h

The filter code is what relies on some default dpi configuration to apply
pointer acceleration and expects the input coordinates to be pre-scaled to
that resolution.

Let's move the define here so we can use it from the touchpad code too.

No functional changes.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Change default DPI to 1000

400 used to be the default DPI for many mice but it it's not anymore. A survey
of mice shows that 400 is still common as one of the pre-configured settings
in switchable multi-resolution gaming mice, but devices with a single
resolution mostly favor 1000 dpi.

Let's make that switch now so that any future changes to the pointer
acceleration code assumes that resolution as a default.

For the touchpad, this has a bad side-effect, caused by our expectation of
mouse vs touchpad behaviours: our acceleration code ignores device type and
provides the same acceleration for the same physical movement. Unfortunately,
we expect touchpads to be significantly slower than mice.

The previous 400 DPI worked because it caused an acceptable slowdown on input.
e.g. on the T440 with a res of 42 units/mm, the scale coefficient was 0.37.
For 1000 DPI as default, this now results in 0.94, i.e. speeding up the
touchpad by a factor of 2.5. That is way too fast.

Adding touchpad-specific filter code is a bigger project, so let's just add a
fixme for now and scale the coefficient back to what it was before the
DPI default change. Effect: touchpad behaves as before.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>