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

[Chenhui Zhao <chenhui.zhao@freescale.com>]

On Sat, Aug 1, 2015 at 8:14 AM, Scott Wood <scottwood@freescale.com> 
wrote:
> On Fri, 2015-07-31 at 17:20 +0800, b29983@freescale.com wrote:
>>  From: Tang Yuantian <Yuantian.Tang@freescale.com>
>> 
>>  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@freescale.com>
>>  Signed-off-by: Tang Yuantian <Yuantian.Tang@feescale.com>
>>  ---
>>   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