> Tell the hardware where to send input, ...

I agree you need a driver but for most hardware, that should be pretty simple, and easily documented by the hardware vendor, shouldn't it? A button has to be about the simplest possible I/O device imaginable.

Yeah, problem is it's likely an acpi button, which ties you into all the fun of that.

Of course, ACPI is supposed to make interfacing with lots of similar things easier, kind of, so there you go.