Can anyone suggest some good references for writing a touchpad driver for linux. Where would I get hardware documentation from. I have read most of the linux device driver books and now I want to take it to the next level.
Are you sure there is no current support for your sentelic in linux kernel? Take a look at Documentation/input/sentelic.txt in Linux source code. If it does not give you direct answers, you'll be able to see how to implement something similar instead. Take a look at its sources, too.
Moreover, if you are not really, really familiar with Linux kernel programming yet, you can read Linux Device Drivers (freely available), Linux Kernel Mode Programming (available, too) and Linux Kernel Development. Some of those sources are somewhat dated, but will give you right ideas about development.