Also I can see an approx 40-50mA change in current from 84 to 396MHz which indicates something is changing.
Uh oh.....You are looking for power saving by dynamically slowing the processor? Just enable CONFIG_PM and let it enter its low power wait at idle. Certainly the easiest way to save power. Also, power management is a whole system design consideration. Unless you are using an x86 processor, the peripheral logic in a system is going to be much more of a power mangement problem than the processor. Low voltage power conversion and LCD backlights are the killers, not the processor. If you are using things like Ethernet PHYs in the product, take a close look at how they can be used in power saving modes. The AMD PHYs are particularly good at this, others may be as well, and do the same kind of analysis for all of the parts on the board.
If you are changing the processor speed, you are going to have to look carefully how it affects the system bus and the SDRAM timing. The list goes on.....effective power management is tedious and challenging...been there, done that quite a bit with this particular processor. It's very system dependent. The stuff in the Linux kernel is a good starting point, but everything from the applications to the additions you will have to make in the kernel are going to be required.
Have fun!
-- Dan
