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Dealing with possessed TrackPoints on later model ThinkPads

Benjamin Slade

On a new-to-me ThinkPad T440p, I’ve had the worst time with the TrackPoint.

First, the stock configuration has a horrible touchpad - which shouldn’t matter if you don’t use the touchpad, but the horribleness of it is that the physical buttons that should be on the top of the touchpad, and are on the touchpads of models preceding and following the **40 line, are not there. But one can replace it, and so I did.

The T440p is nice in that servicing the fan and other internals of the machine is a relatively easy affair compared to say an X230. Just undo two screws on the bottom of the laptop and slide off the back panel, and you have access to memory, drives, the CPU, and so on. And so swapping in a different CPU was really easy and painless.

On the other hand, changing the touchpad was a very involved affair. But it can be done.

However, still the mouse-cursor experience for the machine continued to be horrible. Firstly, there was significant “drift” of the TrackPoint. I.e., even once pressure is released, it keeps moving, for a long time.

However, this ends up being solvable via

sudo -s echo  'ACTION=="add",SUBSYSTEM=="input",ATTR{name}=="TPPS/2 IBM TrackPoint",ATTR{device/drift_time}="30"'  > /etc/udev/rules.d/10-trackpoint.rules

(If you’re trying to do this in Guix, something like:

(define %trackpoint-drift-rule
    (string-append "ACTION==\"add\",SUBSYSTEM==\"input\",ATTR{name}==\"TPPS/2 IBM TrackPoint\",ATTR{device/drift_time}=\"25\""))
(define %my-desktop-services
   (cons (udev-rules-service 'trackpoint-drift %trackpoint-drift-rule)
         (modify-services %desktop-services
                          ....) ; other modifications here
      (service openssh-service-type)
      (service cups-service-type)
      (service nix-service-type)


But, unfortunately, this doesn’t solve what is actually the most horrible issue: the mouse cursor sometimes, when in use, just teleports around the edges of the screen and starts randomly clicking on things.

I finally turned up some discussion of this issue (though not for the T440p specifically) at: https://bugzilla.kernel.org/show_bug.cgi?format=multiple&id=209167 (The discussion suggests that it should somehow be solved in the kernel, but that is not my experience, even running kernel 5.17.13.)

And found that adding psmouse.proto=imps to the kernel arguments and disabling the touchpad in the stock BIOS solves the “possessed mouse cursor” issue. For better or worse, it seem to make the TrackPoint be detected as a generic PS/2 mouse. Which means that drift_time can no longer be set, and I do get a little bit of drift from time to time, but it’s not too bad and certainly is far less maddening than the “possessed mouse cursor” behaviour.

For Guix, the way to implement this is something along the lines of:

 (kernel-arguments (cons* "modprobe.blacklist=pcspkr,snd_pcsp" "psmouse.proto=imps" "acpi_osi=Linux" %default-kernel-arguments))

(The other kernel arguments are simply the other ones I use, and are not directly connected with this issue.)

Depending on the model of ThinkPad and/or the environment, using psmouse.proto=bare instead may work better (see discussion at: https://www.reddit.com/r/thinkpad/comments/v7vn0o/thinkpad_t440p_trackpoint_occasionally_going_crazy/icjkk0o/ ).

So, perhaps not an entirely satisfactory solution, this impish exorcism, but better than alternatives.