[PATCH] ARM: irq_work: Do not attempt to IPI on non IPI-capable HW

[Peter Chen]

On Tue, Aug 16, 2016 at 11:26 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
> Not all of the ARM HW is IPI capable (i.e. most of the non-SMP
> systems). Unfortunately, some systems do advertise being SMP
> capable, even if they have a single core and do not define
> a cross call method.

Could you example it? I find all current set_smp_cross_call is defined
under CONFIG_SMP.
Or you will change gic code to define set_smp_cross_call at runtime?

> In this case, irq_work_queue dies
> as arch_irq_work_has_interrupt() fails to detect this
> particular case.
>
> Let's redefine arch_irq_work_has_interrupt() to actually check
> if we're IPI capable instead of simply being SMP. This sidesteps
> the issue entierely.
>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
>  arch/arm/include/asm/irq_work.h | 6 +++++-
>  arch/arm/include/asm/smp_plat.h | 2 ++
>  arch/arm/kernel/smp.c           | 2 +-
>  3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/irq_work.h b/arch/arm/include/asm/irq_work.h
> index 712d03e..3ba3583 100644
> --- a/arch/arm/include/asm/irq_work.h
> +++ b/arch/arm/include/asm/irq_work.h
> @@ -5,7 +5,11 @@
>
>  static inline bool arch_irq_work_has_interrupt(void)
>  {
> -       return is_smp();
> +#ifdef CONFIG_SMP

Why not using is_smp as condition, it is more strict.

if (is_smp())
    return !!__smp_cross_call;
else
    return false;

Peter

> +       return !!__smp_cross_call;
> +#else
> +       return false;
> +#endif
>  }
>
>  #endif /* _ASM_ARM_IRQ_WORK_H */
> diff --git a/arch/arm/include/asm/smp_plat.h b/arch/arm/include/asm/smp_plat.h
> index f908071..ffee073 100644
> --- a/arch/arm/include/asm/smp_plat.h
> +++ b/arch/arm/include/asm/smp_plat.h
> @@ -26,6 +26,8 @@ static inline bool is_smp(void)
>  #endif
>  }
>
> +extern void (*__smp_cross_call)(const struct cpumask *, unsigned int);
> +
>  /**
>   * smp_cpuid_part() - return part id for a given cpu
>   * @cpu:       logical cpu id.
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index 8615216..f9d771f 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -465,7 +465,7 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
>         }
>  }
>
> -static void (*__smp_cross_call)(const struct cpumask *, unsigned int);
> +void (*__smp_cross_call)(const struct cpumask *, unsigned int);
>
>  void __init set_smp_cross_call(void (*fn)(const struct cpumask *, unsigned int))
>  {
> --
> 2.1.4
>
>
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