How to pesistently configure a Macmini4,1 to boot after power failure?
The correct solution is to execute:

setpci -s 00:03.0 0x7b.b=0x19


Be carefull that this line is for this model, for other models read the full article from http://www.mythic-beasts.com/support/macminicolo_howto.html

Also, put this in rc.local, for some strange reason it block the computer if I put it in grub.cfg