[gentoo-embedded] writing device drivers howto

Hi list!

This is some sort of offtopic, but I guess this is the best point to ask.
I have an embedded system running linux. I need to access some special 
registers (e.g. containing the clock cycles, ...) So I managed to write a 
very simple module, which is able to access the registers. But what makes 
me worrying now, is the way, I have to get the data into my user-space 
application. Is there some documentation, concerning writing device 
drivers and accessing them from the user space anywhere? I found some 
documentation, but either I did not understand the part about getting data 
from kernel space into user space, or it was just simply missing.

Maybe anyone here can help me out!

Thanks in advance and kind regards!

Bye,
Andy