re are many patches to the cpufrequency control - and many are unstable. If your System locks-Hard - y... frequency scaling by loading the longhaul module and some governors:
modprobe longhaul
modprobe c... oaded at every boot. For this - just add longhaul and cpufreq_powersave into the /etc/modprobe.preload... up to 800MHz in this special case - if required - and when idle again - go down with the frequency. In