I installed Ubuntu on my laptop recently, it’s an old Fujitsu-Siemens S6120D, but despite finding others who got it working, my touchpad was just being recognised as a generic PS/2 mouse when I used:

cat /proc/bus/input/devices

in a terminal window.

After a lot of searching I found a post that indicated removing and ‘finding’ the mouse made it display as the ALPS touchpad that it is:

sudo rmmod psmouse
sudo modprobe psmouse

The only problem was it meant doing this each time.

I couldn’t find anywhere to add this as an automated solution, but some suggestions made me check my BIOS and I found an option to disable legacy support for USB devices and voila, the touchpad was recognised on boot (so presumably the legacy support meant it was treating it is a normal mouse, or was cutting in before the USB drivers).

So, quick tip in case it comes in useful, if removing and installing the mouse works, check your BIOS and switch off legacy and PS/2 support and see if that solves it.