Having found a way to reliably reproduce the issue I vaguely understand
what is happening.
The kernel psmouse driver probes the TouchPad, reognizes it as a
Synaptic touchpad, and performs Synaptic-specific initialization. This
happens regardless of whether the TouchPad is switched off in the BIOS
or not (!). Then udev recognizes the device and data from the TouchPad
will start appearing on /dev/input/event* (in my case, event5). Then X
gets started and the xinput infrastructure loads its own input drivers
on top of that.
At that point the TouchPad starts to interfere with the physical
buttons. When you touch the TouchPad in a particular manner (e.g. with
your thumb) before you press a button, then release the button, X does
not register a button release event (as per "evtest"), and the button
appears stuck. This happens even if the TouchPad is disabled via xinput
or using "synclient TouchpadOff=1". It does appear that something
somewhere gets confused by the TouchPad button press, even if the
TouchPad is supposed to be disabled. (I have tried a variety of
synclient/xinput properties, none of them make any difference.)
The issue can be worked around by preventing creation of the device
nodes for the TouchPad. Since the BIOS setting to disable the TouchPad
does not work reliably (or at all?), that means working around the
Synaptics probe in the psmouse kernel module.
So below is another workound, which builds on the workaround in #49.
Basically it unloads the kernel psmouse driver, then reloads it with the
"bare" mouse protocol. This way the TouchPad is not recognized as a
TouchPad any longer, but it also means the TrackPoint is also no longer
recognized as a TrackPoint, so the xorg config files need to specify
"PS/2 Generic Mouse".
1. Step 4 of #49 needs to be replaced by:
Section "InputClass"
Identifier "TrackPoint"
MatchProduct "PS/2 Generic Mouse"
MatchDevicePath "/dev/input/event*"
Option "EmulateWheel" "1"
Option "EmulateWheelButton" "2"
Option "Emulate3Buttons" "0"
Option "XAxisMapping" "6 7"
Option "YAxisMapping" "4 5"
Driver "evdev"
EndSection
2. In /etc/rc.local add:
modprobe -r psmouse
modprobe psmouse proto=bare
With this workaround I can no longer reproduce the problem, also after
sleep/hibernate cycles. Still it remains a nasty workaround: the
TouchPad is dead and system upgrades can easily probably break this
workaround at some point, so I hope that the additional information is
useful in solving the underlying problem.
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https://bugs.launchpad.net/bugs/1506817
Title:
left TPP/2 IBM TrackPoint "sticks on" randomly (X250 15.04)
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