Re: PowerMac PMU programming

Hi Ben,

Looking at this again, so bringing up this thread, although it is 4
months old.

On Tue, 12 Jun 2012 07:24:22 +1000
Benjamin Herrenschmidt [off-list ref] wrote:

On Sun, 2012-06-10 at 23:31 -0400, Justin Hibbits wrote:
=20

quoted

I'll settle on just getting the CPU speed change working, losing
333MHz on my TiBook is a few too many MHz for the poor thing to
lose :)  I do have a desktop, but that's my development platform,
so needs to be at least somewhat stable, so my TiBook is my guinea
pig.
=20
I've googled everything I can think of, but do you know of any
definitive PMU documentation?  Or can you give me any hints on
what's needed just for that simple operation?

=20
No doco no, Darwin and Linux source code are your best bet.
=20
It works like sleep as in: you send the switch command and the PMU
will reboot the processor with the new frequency whenever the
processor enters NAP mode.
=20
This is tricky because there's a loss of cache coherency vs. ongoing
DMAs, hence tricky bits of code in there to deal with the various
caches.
=20

quoted

I noticed that you wind down the ADB queue before killing the PMU.
Is this necessary?  I only disable the interrupt by writing 0x10 to
the IER, but our interrupt model for the PMU is different from the
Linux one.=20

=20
Well that will not disable CB1 (or the external GPIO one). You need to
make sure no other communication with the PMU takes place once you've
sent the sleep command and until you're back.
=20

quoted

 Is it also necessary to disable the interrupt input, even though
the register write should be disabling the PMU's asserting of the
line?  There doesn't seem to be much more different than that, and
setting the openpic priority, Linux sets it to 0x0f but I didn't see
anything in OS X doing that (might that be a problem, too?)
=20
I would love to get my TiBook using the full 1GHz.

=20
I don't remember what openpic does in Darwin, I think interrupts are
all masked there as a side effect of the code in KeyLargo.cpp but I'm
not sure that applies to frequency changes.
=20
Cheers,
Ben.

=46rom looking at the Linux PMU source, and the FreeBSD source, I can see
only cosmetic differences.  However, the biggest thing I see between
the Linux PPC code and the FreeBSD code is that Linux quiesces Open
Firmware right away.  I haven't tried this with FreeBSD yet, but from
your experience with development on this platform, would you think that
not quiescing OFW might cause the catatonic state?

- Justin