help with 7447A dynamic frequency scaling support

[John Steele Scott]

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Hi all,

I have been trying to add cpufreq support to the ppc 7447A chip for my iBook
G4. This entails flipping the DFS bit in HID1 to enable/disable dynamic
frequency scaling (which divides the CPU clock speed by 2).

When I first tried this, it looked like it worked to some extent, but then the
system would lock-up under load soon after switching frequency. One thing I
noticed was that it appears that when the system boots, the DFS bit is set,
i.e. the CPU is only running at half-speed on boot.

So I started again from a fresh set of sources, and this time tried to just
clear the DFS bit so that the system would boot with the CPU at full speed.
However, now the system locks up when it gets to "INIT: version 2.84
booting".

Can anyone suggest why this might occur? I have looked at other cpu-specific
areas of the ppc code, but nothing seems relevant to my situation. I am new
to kernel hacking, but maybe someone with experience has seen this kind of
thing before.

cheers,

John
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