PowerMac PMU programming

Justin Hibbits chmeeedalf at gmail.com
Sun Oct 21 13:56:20 EST 2012

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 <benh at kernel.crashing.org> wrote:

> On Sun, 2012-06-10 at 23:31 -0400, Justin Hibbits wrote:
> > 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.
> > 
> > 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?
> No doco no, Darwin and Linux source code are your best bet.
> 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.
> 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.
> > 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. 
> 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.
> >  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?)
> > 
> > I would love to get my TiBook using the full 1GHz.
> 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.
> Cheers,
> Ben.

From 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

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