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