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

[Chenhui Zhao]

On Sat, Aug 1, 2015 at 8:14 AM, Scott Wood <scottwood@xxxxxxxxxxxxx> 
wrote:
> On Fri, 2015-07-31 at 17:20 +0800, b29983@xxxxxxxxxxxxx wrote:
> >  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>
> >  ---
> >   arch/powerpc/Kconfig              |  2 +-
> >   arch/powerpc/include/asm/smp.h    |  1 +
> >   arch/powerpc/kernel/smp.c         |  5 +++++
> >   arch/powerpc/platforms/85xx/smp.c | 39 
> > ++++++++++++++++++++++++++++++++----
> >  ---
> >   4 files changed, 39 insertions(+), 8 deletions(-)
> >
> >  diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> >  index 5ef2711..dd9e252 100644
> >  --- a/arch/powerpc/Kconfig
> >  +++ b/arch/powerpc/Kconfig
> >  @@ -386,7 +386,7 @@ config SWIOTLB
> >   config HOTPLUG_CPU
> >        bool "Support for enabling/disabling CPUs"
> >        depends on SMP && (PPC_PSERIES || \
> >  -     PPC_PMAC || PPC_POWERNV || (PPC_85xx && !PPC_E500MC))
> >  +     PPC_PMAC || PPC_POWERNV || FSL_SOC_BOOKE)
> >        ---help---
> >          Say Y here to be able to disable and re-enable individual
> >          CPUs at runtime on SMP machines.
>
>
>
> >  diff --git a/arch/powerpc/include/asm/smp.h 
> > b/arch/powerpc/include/asm/smp.h
> >  index 825663c..bf37d17 100644
> >  --- a/arch/powerpc/include/asm/smp.h
> >  +++ b/arch/powerpc/include/asm/smp.h
> >  @@ -67,6 +67,7 @@ void generic_cpu_die(unsigned int cpu);
> >   void generic_set_cpu_dead(unsigned int cpu);
> >   void generic_set_cpu_up(unsigned int cpu);
> >   int generic_check_cpu_restart(unsigned int cpu);
> >  +int generic_check_cpu_dead(unsigned int cpu);
> >   #endif
> >
> >   #ifdef CONFIG_PPC64
> >  diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> >  index ec9ec20..2cca27a 100644
> >  --- a/arch/powerpc/kernel/smp.c
> >  +++ b/arch/powerpc/kernel/smp.c
> >  @@ -454,6 +454,11 @@ int generic_check_cpu_restart(unsigned int cpu)
> >        return per_cpu(cpu_state, cpu) == CPU_UP_PREPARE;
> >   }
> >
> >  +int generic_check_cpu_dead(unsigned int cpu)
> >  +{
> >  +     return per_cpu(cpu_state, cpu) == CPU_DEAD;
> >  +}
>
> Is there a non-generic check_cpu_dead()?

NO, just follow the name "generic_check_cpu_restart()".

> It gets open-coded in generic_cpu_die()... Either open-code it 
> elsewhere, or
> call it check_cpu_dead() and use it everywhere there's a CPU_DEAD 
> check.
>
>
> >  +
> >   static bool secondaries_inhibited(void)
> >   {
> >        return kvm_hv_mode_active();
> >  diff --git a/arch/powerpc/platforms/85xx/smp.c
> >  b/arch/powerpc/platforms/85xx/smp.c
> >  index 6811a5b..7f0dadb 100644
> >  --- a/arch/powerpc/platforms/85xx/smp.c
> >  +++ b/arch/powerpc/platforms/85xx/smp.c
> >  @@ -42,6 +42,7 @@ struct epapr_spin_table {
> >        u32     pir;
> >   };
> >
> >  +#ifdef CONFIG_HOTPLUG_CPU
> >   static u64 timebase;
> >   static int tb_req;
> >   static int tb_valid;
> >  @@ -111,7 +112,7 @@ static void mpc85xx_take_timebase(void)
> >        local_irq_restore(flags);
> >   }
> >
> >  -#ifdef CONFIG_HOTPLUG_CPU
> >  +#ifndef CONFIG_PPC_E500MC
> >   static void e500_cpu_idle(void)
>
> What happens if we bisect to patch 1/3 and run this on e500mc?
>
> Please move the ifdef to that patch.

OK.

> >   {
> >        u32 tmp;
> >  @@ -127,6 +128,7 @@ static void e500_cpu_idle(void)
> >        mtmsr(tmp);
> >        isync();
> >   }
> >  +#endif
> >
> >   static void qoriq_cpu_dying(void)
> >   {
> >  @@ -144,11 +146,30 @@ static void qoriq_cpu_dying(void)
> >
> >        generic_set_cpu_dead(cpu);
> >
> >  +#ifndef CONFIG_PPC_E500MC
> >        e500_cpu_idle();
> >  +#endif
> >
> >        while (1)
> >                ;
> >   }
> >  +
> >  +static void qoriq_real_cpu_die(unsigned int cpu)
>
> Real as opposed to...?

It's hard to find a good name. :)

> >  +{
> >  +     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.

> >   #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.

-Chenhui

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