NAP mode on powerpc 970

Jake Moilanen moilanen at
Sat Jan 17 05:01:19 EST 2004

> I was not able to find anything related to the NAP mode in the ppc64
> branch.

Linux does not support NAP mode for the 970's.  Going to this mode
powers off the caches (thus killing the caches).  There are some other
potential issues (thermal, and power supply).

This should not be done in Linux in the first place.  The correct place
is in the FW.

> Is there somebody who try to patch the idle loop of the ppc64 branch as
> it is already done in the ppc32 branch for some ppc processors ?
> The other related issue I have is how to enable the NAP mode by setting
> the hypervisor HID0 register. Is there a way to write the hypervisor
> register through the kernel ? through the firmware of the JS20 ?

Yes, bit 9 on HID0 needs to be set then the POW bit in the MSR (bit
45).  This will quiesce the processor and prefetch engine and put you
into doze mode.  The buses will get the quiesced next and once they are
you will be in NAP mode.  Any interrupt will kick you back to full-power

HID0 is a hypervisor resource and linux does not have access to it.

There is more information in book 4 of the 970.


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