Date: Thu, 6 Aug 2015 13:54:26 +0800
From: Chenhui Zhao <chenhui.zhao@freescale.com>
Subject: Re: [PATCH 1/3] Powerpc: mpc85xx: refactor the PM operations
To: Scott Wood <scottwood@freescale.com>
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        <linux-kernel@vger.kernel.org>,
        Tang Yuantian <Yuantian.Tang@freescale.com>,
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On Thu, Aug 6, 2015 at 1:46 PM, Scott Wood <scottwood@freescale.com> 
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@freescale.com>
>>  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@freescale.com>
>>  > >  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@freescale.com>
>>  > >  > >  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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