Description of problem:
When scrolling using the two-finger scroll on the touchpad of my ASUS N550JV, for example when reading a PDF in Evince, the scroll sensitivity is really high, leading to difficulties in positioning the view as desired. This happens in other GTK-based applications too, like Corebird or Evolution.

As a side effect, this high sensitivity leads to the kinetic scroll implemented in GTK3 to make the view bounce up or down when the finger is lifted from the touchpad. This is due to the small movements registered by the touchpad when the finger is lifted, even if it was kept still before lifting it.


Version-Release number of selected component (if applicable):
gtk3.x86_64 - 3.22.26-2.fc27


How reproducible:
An ASUS N550JV is necessary, but other laptops with an "ETPS/2 Elantech Touchpad" may have the same problem.


Steps to Reproduce:
1. Install Fedora 27 on an ASUS N550JV or boot with a live USB stick.
2. Open a PDF with Evince.
3. Try scrolling through the pages.


Actual results:
The movement through the PDF is really fast, allowing to scroll 6 pages (at 100% zoom) just moving the two fingers from top to bottom on the touchpad.

When trying to center a particular page on the screen and then lifting the fingers from the touchpad, the view bounces up or down, due to the small scroll events registered when lifting the finger.


Expected results:
The pages should scroll at a lower speed (scrolling around 2 pages at 100% zoom when going from top to bottom on the touchpad), allowing for a more controlled movement of the view. (The two pages measure is taken from what happens on a Dell XPS 13)

When stopping the finger to center a certain page and then lifting it from the touchpad, the view should stay still instead of moving due to the kinetic scrolling.


Additional info:
This bug was first reported against libinput (bug 1557680), but I received a reply suggesting to file it against GTK since libinput "exports scrolling as an axis in a defined range and relation to pointer movement" and thus it is up to the graphic library to actually handle correctly the speed at which the view is scrolled in relation to the movement.

I would like to point out that the scrolling speed does not seem to be affected by the "Touchpad speed" setting in GNOME Settings. Moreover, there is no difference in behavior between X and Wayland. On applications like Chrome or Okular the scrolling is slower (approximately a half of the one for GTK applications).

I would also like to add that my touchpad resolution is correct, I have already checked it and fixed it with a temporary rule in hwdb.d. The actual fix was already accepted in systemd/master and will be released with the next version.