Subject: Re: [PATCH 4/9] powerpc/85xx: support CPU hotplug for e500mc and e5500

From: Chenhui Zhao <[email-masked]>
Date: Wed, 12 Mar 2014 12:34:07 +0800

On Tue, Mar 11, 2014 at 06:48:13PM -0500, Scott Wood wrote:
> On Fri, 2014-03-07 at 12:58 +0800, Chenhui Zhao wrote:
> > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> > index ac2621a..f3f4401 100644
> > --- a/arch/powerpc/kernel/smp.c
> > +++ b/arch/powerpc/kernel/smp.c
> > @@ -405,8 +405,12 @@ void generic_cpu_die(unsigned int cpu)
> >  
> >  	for (i = 0; i < 100; i++) {
> >  		smp_rmb();
> > -		if (per_cpu(cpu_state, cpu) == CPU_DEAD)
> > +		if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
> > +#ifdef CONFIG_PPC64
> > +			paca[cpu].cpu_start = 0;
> > +#endif
> 
> Why wasn't this needed by previous ppc64 machines?

If not clear, cpu can't start in the case of cpu hotpolug.
The function pseries_cpu_die() in arch/powerpc/platforms/pseries/hotplug-cpu.c
also clears the flag.

> 
> > diff --git a/arch/powerpc/platforms/85xx/smp.c b/arch/powerpc/platforms/85xx/smp.c
> > index 2e5911e..0047883 100644
> > --- a/arch/powerpc/platforms/85xx/smp.c
> > +++ b/arch/powerpc/platforms/85xx/smp.c
> > @@ -19,6 +19,7 @@
> >  #include <linux/kexec.h>
> >  #include <linux/highmem.h>
> >  #include <linux/cpu.h>
> > +#include <linux/smp.h>
> >  
> >  #include <asm/machdep.h>
> >  #include <asm/pgtable.h>
> > @@ -46,6 +47,17 @@ static u64 timebase;
> >  static int tb_req;
> >  static int tb_valid;
> >  
> > +#ifdef CONFIG_PPC_E500MC
> > +/* specify the cpu PM state when cpu dies, PH15/NAP is the default */
> > +int qoriq_cpu_die_state = E500_PM_PH15;
> > +#endif
> 
> static?  Is there any way to modify this other than modifying source
> code?
> 
> BTW, QorIQ doesn't imply an e500mc derivative.

Will support e500, but for now these code support e500mc derivative in
advance.

Supposed qoriq_cpu_die_state can be changed by platform init code
if the default value is not proper for a specific platform.

> 
> > @@ -125,6 +138,34 @@ static void mpc85xx_take_timebase(void)
> >  }
> >  
> >  #ifdef CONFIG_HOTPLUG_CPU
> > +#ifdef CONFIG_PPC_E500MC
> > +static void qoriq_cpu_die(void)
> > +{
> > +	unsigned int cpu = smp_processor_id();
> > +
> > +	local_irq_disable();
> > +#ifdef CONFIG_PPC64
> > +	__hard_irq_disable();
> > +#endif
> 
> Why this instead of one call to hard_irq_disable() (no leading
> underscores)?
> 
> -Scott

hard_irq_disable() will clear soft_enabled again. local_irq_disable()
has cleared it.

Will use hard_irq_disable() to replace these lines.

  local_irq_disable();
  #ifdef CONFIG_PPC64
  	__hard_irq_disable();
  #endif

-Chenhui