There's a WIP Libinput driver patch that would expose the API that we could hook into from the touchpad KCM: https://gitlab.freedesktop.org/xorg/driver/xf86-input-libinput/merge_requests/12

I have libinput 1.15 on my Neon laptop, and I can see the new UI, and it works. Thanks.

Well Tim Richardson, I wonder how you can have a UI for this when we have no implementation for it and upstream has not landed their patch yet.
I guess You meant something else than "scroll by n lines" for touchpad that we talk about here.

I interpreted this bug as 'no UI to configure touchpad scroll sensitivity/speed'. At least, this was the interpretation that I responded to. Such as UI was missing, and then it was added, hence my reference to the new UI, which was actually what I wanted all along. Maybe Nate's initial comment does not make sense, he goes from "scroll by n lines" to speed/sensitivity. They are different things. Scroll by n lines is mouse wheel to me.

Although changing the pointer speed in the touchpad kcm does not actually seem to change the speed of two finger scrolling, which I obviously don't use very much. 
So in fact I actually confirm that there is a touchpad kcm when using libinput, and pointer sensitivity can be controlled, but there is no control over  scrolling sensitivity.

(In reply to Tim Richardson from comment #5)
> Although changing the pointer speed in the touchpad kcm does not actually
> seem to change the speed of two finger scrolling, which I obviously don't
> use very much. 
> So in fact I actually confirm that there is a touchpad kcm when using
> libinput, and pointer sensitivity can be controlled, but there is no control
> over  scrolling sensitivity.

So basically you mixed up a setting for pointer sensitivity with scroll sensitivity?

Also, what do you mean with "new UI"?

"New UI": libinput exposes a number of configurations for touchpads. For a long time, most of these options were not exposed to the touchpad kcm. This changed in Jan 2020 when a much richer kcm arrived, hence "new UI".

Ah, I wasn't aware of that. Thanks for mentioning!

Git commit 564c739371c8076728c264154847316c64e4c1ec by Méven Car.
Committed on 07/04/2020 at 17:08.
Pushed by meven into branch 'master'.

Wayland: Allow to set a scroll Factor for input devices

Summary:
Mouse and touchpad wheel events are concerned.

KCM patch: D28331

Test Plan: build, ctest, manual set of scrollfactor value via qdbusviewer

Reviewers: #kwin, davidedmundson, zzag, bport, ervin, apol

Reviewed By: #kwin, davidedmundson, ervin, apol

Subscribers: apol, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D28310

M  +24   -0    autotests/libinput/device_test.cpp
M  +23   -2    libinput/device.cpp
M  +12   -0    libinput/device.h
M  +2    -2    libinput/events.cpp

https://commits.kde.org/kwin/564c739371c8076728c264154847316c64e4c1ec

Git commit 0cf73170479bb271fb7498e67d38d3c6255594a4 by Méven Car.
Committed on 07/04/2020 at 17:09.
Pushed by meven into branch 'master'.

KCM/mouse KCM/touchpad: Add a Scroll speed setting for wayland

Summary:
Depends on D28310
FIXED-IN: 5.19.0

Test Plan: {F8201345}

Reviewers: #kwin, #plasma, davidedmundson, ervin, bport, crossi, hchain

Reviewed By: ervin

Subscribers: ngraham, zzag, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28331

M  +7    -1    kcms/mouse/backends/kwin_wl/kwin_wl_device.cpp
M  +11   -0    kcms/mouse/backends/kwin_wl/kwin_wl_device.h
M  +63   -0    kcms/mouse/kcm/libinput/main.qml
M  +5    -0    kcms/touchpad/src/backends/kwin_wayland/kwinwaylandtouchpad.cpp
M  +18   -0    kcms/touchpad/src/backends/kwin_wayland/kwinwaylandtouchpad.h
M  +63   -0    kcms/touchpad/src/kcm/libinput/touchpad.qml

https://commits.kde.org/plasma-desktop/0cf73170479bb271fb7498e67d38d3c6255594a4

*** Bug 401954 has been marked as a duplicate of this bug. ***