I still don't know a real solution to this. Most of the time it just does not work at all. This is not deterministic. Something goes wrong almost every time when the driver takes over and then i have no chance to see what's going on. It would be nice if some kind of error message shows up but the screen only goes black.
Boot -> grub -> first Messages appear -> num lock key lit -> screen goes black, num lock key unlit, FAN spins up, nothing happens, keyboard unresponsive, only the Magic SysRq Reboot works.