Re: [PATCH 1/3] Powerpc: mpc85xx: refactor the PM operations

From: Chenhui Zhao
Date: Thu Aug 06 2015 - 01:55:10 EST



On Thu, Aug 6, 2015 at 1:46 PM, Scott Wood <scottwood@xxxxxxxxxxxxx> wrote:
On Thu, 2015-08-06 at 12:20 +0800, Chenhui Zhao wrote:
On Thu, Aug 6, 2015 at 10:57 AM, Scott Wood <scottwood@xxxxxxxxxxxxx>
wrote:
> On Wed, 2015-08-05 at 18:11 +0800, Chenhui Zhao wrote:
> > On Tue, Aug 4, 2015 at 4:26 AM, Scott Wood <scottwood@xxxxxxxxxxxxx>
> > wrote:
> > > On Mon, 2015-08-03 at 19:32 +0800, Chenhui Zhao wrote:
> > > > >
> > >
> > > > On Sat, Aug 1, 2015 at 7:59 AM, Scott Wood
> > <scottwood@xxxxxxxxxxxxx>
> > > > wrote:
> > >
> > > > >
> > > > > Could you explain irq_mask()? Why would there still be IRQs
> > > > destined
> > > > > for
> > > > > this CPU at this point?
> > > >
> > > > This function just masks irq by setting the registers in RCPM
> > (for
> > > > example, RCPM_CPMIMR, RCPM_CPMCIMR). Actually, all irqs to
> > this CPU
> > > > have been migrated to other CPUs.
> > >
> > > So why do we need to set those bits in RCPM? Is it just caution?
> >
> > Setting these bits can mask interrupts signalled to RCPM from MPIC
> > as a
> > means of
> > waking up from a lower power state. So, cores will not be waked up
> > unexpectedly.
>
> Why would the MPIC be signalling those interrupts if they've been
> masked at
> the MPIC?
>
> -Scott
>

The interrupts to RCPM from MPIC are IRQ, Machine Check, NMI and
Critical interrupts. Some of them didn't be masked in MPIC.

What interrupt could actually happen to a sleeping cpu that this protects
against?

-Scott

Not sure. Maybe spurious interrupts or hardware exceptions. However, setting them make sure dead cpus can not be waked up unexpectedly.

-Chenhui

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