Set the mouse prototype depending on the model or mouse it boots.
My current librem 13 v2 prototype has a fried touchpad, once I receive the final hardware, I'll be able to test and provide proper logs. For now, all I can say is that MrChromeBox who tested it on his prototype said that mouse scrolling/multitouch doesn't work in PureOS but works in GalliumOS. Also, when he tried to remove psmouse module then re-insert it with proto=imps, he said that it broke scrolling in GalliumOS.
The logs I have from before the mouse was fried had this in dmesg :
dmesg.log:[ 2.330945] mousedev: PS/2 mouse device common for all mice dmesg.log:[ 3.928606] psmouse serio1: elantech: assuming hardware version 4 (with firmware version 0x361f00) dmesg.log:[ 3.971528] psmouse serio1: elantech: Synaptics capabilities query result 0x00, 0x16, 0x0d. dmesg.log:[ 4.013740] psmouse serio1: elantech: Elan sample query result 00, 49, 75
Note: I got it working on the Librem 15. I removed the /etc/modules.d/purism-psmouse.conf and did modprobe -r psmouse && modprobe psmouse, that fixed the multitouch. Note though that on reboot, I had to do the modprobe again because it was loaded with the wrong options by default even if the /etc/modprobe file wasn't there.