Re: [PATCH 2/3] PowerPC/mpc85xx: Add hotplug support on E5500 and E500MC cores

[Chenhui Zhao]

On Tue, Aug 4, 2015 at 5:18 AM, Scott Wood <scottwood@xxxxxxxxxxxxx> 
wrote:
> [Added linuxppc-dev@xxxxxxxxxxxxxxxxx  Besides that list being 
> required for
> review of PPC patches, it feeds the patchwork that I use to track and 
> apply
> patches.]
>
> On Mon, 2015-08-03 at 19:52 +0800, Chenhui Zhao wrote:
> >  On Sat, Aug 1, 2015 at 8:14 AM, Scott Wood <scottwood@xxxxxxxxxxxxx>
> >  wrote:
> >  > On Fri, 2015-07-31 at 17:20 +0800,  b29983@xxxxxxxxxxxxxxxxxx:
> >  > >  From: Tang Yuantian <Yuantian.Tang@xxxxxxxxxxxxx>
> >  > >
> >  > >  Freescale E500MC and E5500 core-based platforms, like P4080, 
> > T1040,
> >  > >  support disabling/enabling CPU dynamically.
> >  > >  This patch adds this feature on those platforms.
> >  > >
> >  > >  Signed-off-by: Chenhui Zhao <chenhui.zhao@xxxxxxxxxxxxx>
> >  > >  Signed-off-by: Tang Yuantian <Yuantian.Tang@xxxxxxxxxxxx>


> >  +{
> >  > >  +     int i;
> >  > >  +
> >  > >  +     for (i = 0; i < 50000; i++) {
> >  > >  +             if (generic_check_cpu_dead(cpu)) {
> >  > >  +                     qoriq_pm_ops->cpu_die(cpu);
> >  > >  +#ifdef CONFIG_PPC64
> >  > >  +                     paca[cpu].cpu_start = 0;
> >  > >  +#endif
> >  > >  +                     return;
> >  > >  +             }
> >  > >  +             udelay(10);
> >  > >  +     }
> >  > >  +     pr_err("%s: CPU%d didn't die...\n", __func__, cpu);
> >  > >  +}
> >  >
> >  > Only 500ms timeout, versus 10sec in generic_cpu_die()?
> >
> >  The process is fast. Maybe 10 second is too large.
>
> Is it fast 100% of the time?  What if the CPU you intend to die is in 
> a long
> critical section?  What harm is there to having a longer timeout, 
> similar to
> what other platforms use?

Will change the max timeout to 10 seconds.

> >  >
> >  > >   #endif
> >  > >
> >  > >   static inline void flush_spin_table(void *spin_table)
> >  > >  @@ -246,11 +267,7 @@ static int smp_85xx_kick_cpu(int nr)
> >  > >                spin_table = phys_to_virt(*cpu_rel_addr);
> >  > >
> >  > >        local_irq_save(flags);
> >  > >  -#ifdef CONFIG_PPC32
> >  > >   #ifdef CONFIG_HOTPLUG_CPU
> >  > >  -     /* Corresponding to generic_set_cpu_dead() */
> >  > >  -     generic_set_cpu_up(nr);
> >  > >  -
> >  > >        if (system_state == SYSTEM_RUNNING) {
> >  > >                /*
> >  > >                 * To keep it compatible with old boot program 
> > which
> >  > > uses
> >  > >  @@ -263,6 +280,7 @@ static int smp_85xx_kick_cpu(int nr)
> >  > >                out_be32(&spin_table->addr_l, 0);
> >  > >                flush_spin_table(spin_table);
> >  > >
> >  > >  +             qoriq_pm_ops->cpu_up(nr);
> >  >
> >  > Again, is it possible to get here without a valid qoriq_pm_ops 
> > (i.e.
> >  > is there
> >  > anything stopping the user from trying to initiate CPU hotplug)?
> >  >
> >  > -Scott
> >
> >  For every platform running this code, should has a valid 
> > qoriq_pm_ops.
> >  If not valid, it's a bug.
>
> How do you prevent this code from running when there is no valid 
> qoriq_pm_ops?
>
> -Scott

Will check if qoriq_pm_ops is valid.

-Chenhui



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