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

[Scott Wood <scottwood@freescale.com>]

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()?

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.

>  {
>       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...?

> +{
> +     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()?

>  #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