https://bugs.freedesktop.org/show_bug.cgi?id=72921
--- Comment #12 from Arno Schuring aelschuring@hotmail.com --- I have upgraded my bios from 25.1 to 25.3, issue remains. I will browse the BIOS for overclocking settings, but I didn't change any; so if they do effect this, then it's the factory-defaults causing this.
This is a wild guess, but the symptoms to me look like a spurious watchdog kicking in, given that the system appears fully functional right up until the reboot, no errors are logged and there is a delay between the modprobe and the reboot.
@Kertesz: according to Alex in comment #1, "forcing dpm=1 will enable extra debugging output". Possibly that's why you're not seeing those lines.