No "Touchpad Tab" under Mouse and Touchpad settings. Detected as PS/2 Generic Mouse

Try this:

sudo modprobe -r psmouse
sudo modprobe psmouse proto=imps

If it works add both the lines to:

/etc/rc.local

But add them without the leading sudo. So the lines you'll add to /etc/rc.local will look like:

modprobe -r psmouse
modprobe psmouse proto=imps

If /etc/rc.local ends with something like exit 0, make sure to add those lines before that exit line.

I had exact same problem on my Inspiron N5110 running Ubuntu 12.04 but was able to fix it using patch and instructions provided in these two links.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/606238/comments/144

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/606238/comments/147

Touchpad is now recognised as AlpsPS/2 ALPS DualPoint TouchPad and Touchpad tab is enabled in System Settings. Unfortunately, scrolling is still not an option... :-(

At least touchpad is disabled while typing, which was the biggest problem for me resulting in cryptic writings! :-) Also Fn+F3 is working now (aka, touchpad toggle).