I have actually done that on summer in order to test power and thermal profile. Patches with few additional fixes for the Omnia board are here; https://github.com/tmshlvck/omnia-linux/tree/omnia-cpuclk .
Problem is, that it is considered unstable/dangerous feature and it didn’t reduce the overall power and thermal profile so much, to justify testing and stabilization effort needed in order to put it into mainline or/and TurrisOS. If somebody have time to test it extensively and possibly cleanup the work, I will be glad to re-send Gregory’s patches along with my fixes.
Another story is CPU idle support, which is also missing and it seems to be result of a HW bug somewhere in I/O subsystem and that has been temporarily resolved (quite a long time ago) by disabling the CPU idle in this patch https://patchwork.kernel.org/patch/6319581/ . We are investigating this issue in cooperation with Marvell, however I can’t make any guarantees or even assumptions o when or if ever it is going to be resolved without disabling the driver.
However it seems that even with CPU idle and with on-demand cpufreq driver it won’t make that big difference. Our experiments indicate that the difference between full power 1600MHz with 100% CPU utilization and idle at 800MHz was only 1-1.5 watts.