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

On Thu, 2015-08-06 at 13:54 +0800, Chenhui Zhao wrote:

On Thu, Aug 6, 2015 at 1:46 PM, Scott Wood [off-list ref] 
wrote:

quoted

On Thu, 2015-08-06 at 12:20 +0800, Chenhui Zhao wrote:

quoted

 On Thu, Aug 6, 2015 at 10:57 AM, Scott Wood 
[off-list ref]
 wrote:
 > On Wed, 2015-08-05 at 18:11 +0800, Chenhui Zhao wrote:
 > >  On Tue, Aug 4, 2015 at 4:26 AM, Scott Wood 
[off-list ref]
 > >  wrote:
 > >  > On Mon, 2015-08-03 at 19:32 +0800, Chenhui Zhao wrote:
 > >  > >  >
 > >  >
 > >  > >  On Sat, Aug 1, 2015 at 7:59 AM, Scott Wood
 > > [off-list ref]
 > >  > >  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.

Spurious interrupts happen due to race conditions.  They don't happen because 
the MPIC is bored and decides to ring a CPU's doorbell and hide in the bushes.

If by "hardware exceptions" you mean machine checks, how would such a machine 
check be generated by a core that is off?

 However, setting them make sure dead cpus can not be waked up unexpectedly.

I'm not seeing enough value here to warrant resurrecting the old sleep node 
stuff.

-Scott