Once upon a time, when I was working at Edinfor, I was issued a Toshiba Tecra S1 laptop, which was great, except that some of the function keys were “soft keys” that depended on OS support that didn’t exist in the Linux kernel (so, brightness and turning wireless on).
Fortunately, being able to access, modify, and distribute the code is the whole point behind the GPL, so I learned by example and wrote the driver, currently available through the Wayback Machine.
Quoting for the original page:
This is a kernel module that supports all of the features in the the Toshiba Tecra laptop that I have, including LCD brightness, bluetooth and wireless control, Fn key detection, etc.
Be aware that some of the functions will need to have the support of a userland tool, since the Fn keys always return the same scancode to X; what makes the difference is the value that is captured and made available in /proc/acpi/tecra/hotkey. A userland utility can watch the value and take actions (e.g. calling the mixer application, locking the session, etc).
This isn’t very polished yet but it is a start. I hope it will be useful.
Special regards should be made to Thorsten Zachmann for the smi_command that is the bulk of the complex work and to John Belmonte in which module mine was based; also a thank you is in order to Toshiba Linux Support who made available the technical documentation necessary to make this module complete.