Ubuntu – erratic behaviour of trackpoint on thinkpad t420s [UBUNTU 18.04]

I bought recently ThinkPad W540 (high-end type) and that new generation ClickPad has loomed large in my mind... All the time something was wrong in new 14.04. But finally i got it working!

For Ubuntu (14.04 LTS and previous) you need newer evdev and synaptics (until it wont be implemented), to get it work with AUR's arch pkg. I did some fixes and enchantments in script - below you got it's content.

to get it work, open terminal as normal user, go to some work DIR and type:

touch install.sh
chmod +x install.sh
gedit install.sh

than copy/paste script, save and close gedit. Go back to terminal and run it as normal user:

./install.sh

SCRIPT:

#!/bin/bash
echo --------------------------------------------------------------------
echo If you miss some dependances or packages, than install them first...
echo --------------------------------------------------------------------

sudo apt-get install libevdev-dev libevdev2
sudo apt-get build-dep xserver-xorg-input-evdev xserver-xorg-input-synaptics

wget https://launchpad.net/ubuntu/+archive/primary/+files/xserver-xorg-input-evdev_2.9.0.orig.tar.gz
wget https://launchpad.net/ubuntu/+archive/primary/+files/xserver-xorg-input-evdev_2.9.0-1ubuntu1.diff.gz
wget https://launchpad.net/ubuntu/+archive/primary/+files/xserver-xorg-input-evdev_2.9.0-1ubuntu1.dsc

wget https://launchpad.net/ubuntu/+archive/primary/+files/xserver-xorg-input-synaptics_1.8.0.orig.tar.gz
wget https://launchpad.net/ubuntu/+archive/primary/+files/xserver-xorg-input-synaptics_1.8.0-1~exp2ubuntu2.diff.gz
wget https://launchpad.net/ubuntu/+archive/primary/+files/xserver-xorg-input-synaptics_1.8.0-1~exp2ubuntu2.dsc

dpkg-source -x --no-check xserver-xorg-input-evdev_2.9.0-1ubuntu1.dsc
dpkg-source -x --no-check xserver-xorg-input-synaptics_1.8.0-1~exp2ubuntu2.dsc

wget https://aur.archlinux.org/packages/xf/xf86-input-evdev-trackpoint/xf86-input-evdev-trackpoint.tar.gz

tar -xzf xf86-input-evdev-trackpoint.tar.gz

mv xf86-input-evdev-trackpoint arch
mv xserver-xorg-input-evdev-2.9.0 evdev
mv xserver-xorg-input-synaptics-1.8.0 synaptics

cp synaptics/src/{eventcomm.c,eventcomm.h,properties.c,synaptics.c,synapticsstr.h,synproto.c,synproto.h} evdev/src
cp synaptics/include/synaptics-properties.h evdev/src
cp arch/*.patch evdev

cd evdev
patch -p1 -i 0001-implement-trackpoint-wheel-emulation.patch
patch -p1 -i 0004-disable-clickpad_guess_clickfingers.patch
patch -p1 -i 0006-add-synatics-files-into-Makefile.am.patch

dpkg-buildpackage

cd ..
sudo dpkg -i xserver-xorg-input-evdev_*.deb
sudo apt-get remove xserver-xorg-input-synaptics

sudo mkdir /etc/X11/xorg.conf.d/
sudo cp arch/90-evdev-trackpoint.conf /etc/X11/xorg.conf.d

echo If everything was OK, than logout/reboot and enjoy fully working ThinkPad Trackpoint/ClickPad
echo If you want to deactivate touch area of ClickPad for pure TrackPoint usage
echo edit /etc/X11/xorg.conf.d/90-evdev-trackpoint.conf and change "0" to "1" at line
echo Option "AreaBottomEdge" "0" 
echo Regards, T_Send

Believe it or not, I've solved this one. The solution is not specific to either the Aten KVM or the Thinkpad Compact keyboard and might help in the generic "my keyboard does not work with a KVM switch properly".

So the idea is this: kernel driver is trying to initialize the specific device (e.g. a keyboard). However, a KVM switch usually provides convenience shortcuts for switching and other features. In case of Aten there is a shortcut for double-click on the scroll wheel. The switch itself needs to filter USB commandos to get this working which obviously intefers with kernel's ability to set certain configuration bits on the device. In my case, it failed to configure the scrolling functionality.

The soluton is simple: disable the conflicting mode. For the Aten, it's called "mouse emulation mode". Having disabled that, everything started working properly.