While not yet mainline, there is an open-source input driver still being worked on for the Cypress PS/2 Trackpad that's used in the popular Dell XPS 13/15 "Sputnik" laptops and other devices.
Dell, Canonical, and Cypress haven't been quick to work on mainline support for the PS/2 Trackpad, but at last it's looking like it will finally be coming soon. Up to this point users have had to run patched kernels for having a working track-pad.
Hitting the Linux kernel mailing list this afternoon was the 7th kernel patch
for the Cypress PS/2 Trackpad. The new driver also depends upon a "increase struct ps2dev cmdbuf to 8 bytes" patch for it to work.