linux-kernel - Re: [RFC PATCH v2 24/35] drivers: base: Implement weak arch_unregister

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Date:   Tue, 19 Sep 2023 10:59:23 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     James Morse <james.morse@....com>, linux-pm@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-acpi@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev
Cc:     x86@...nel.org, Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com
Subject: Re: [RFC PATCH v2 24/35] drivers: base: Implement weak
 arch_unregister_cpu()



On 9/14/23 02:38, James Morse wrote:
> Add arch_unregister_cpu() to allow the ACPI machinery to call
> unregister_cpu(). This is enough for arm64, riscv and loongarch, but
> needs to be overridden by x86 and ia64 who need to do more work.
> 
> CC: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v1:
>   * Added CONFIG_HOTPLUG_CPU ifdeffery around unregister_cpu
> ---
>   arch/ia64/include/asm/cpu.h      | 4 ----
>   arch/loongarch/include/asm/cpu.h | 6 ------
>   arch/x86/include/asm/cpu.h       | 1 -
>   drivers/base/cpu.c               | 9 ++++++++-
>   4 files changed, 8 insertions(+), 12 deletions(-)
> 

I agree with Jonathan this patch needs to come early. Maybe move this
before the following one:

[RFC PATCH v2 19/35] ACPI: Move acpi_bus_trim_one() before acpi_scan_hot_remove()

> diff --git a/arch/ia64/include/asm/cpu.h b/arch/ia64/include/asm/cpu.h
> index a3e690e685e5..642d71675ddb 100644
> --- a/arch/ia64/include/asm/cpu.h
> +++ b/arch/ia64/include/asm/cpu.h
> @@ -15,8 +15,4 @@ DECLARE_PER_CPU(struct ia64_cpu, cpu_devices);
>   
>   DECLARE_PER_CPU(int, cpu_state);
>   
> -#ifdef CONFIG_HOTPLUG_CPU
> -extern void arch_unregister_cpu(int);
> -#endif
> -
>   #endif /* _ASM_IA64_CPU_H_ */
> diff --git a/arch/loongarch/include/asm/cpu.h b/arch/loongarch/include/asm/cpu.h
> index b8568e637420..48b9f7168bcc 100644
> --- a/arch/loongarch/include/asm/cpu.h
> +++ b/arch/loongarch/include/asm/cpu.h
> @@ -128,10 +128,4 @@ enum cpu_type_enum {
>   #define LOONGARCH_CPU_HYPERVISOR	BIT_ULL(CPU_FEATURE_HYPERVISOR)
>   #define LOONGARCH_CPU_PTW		BIT_ULL(CPU_FEATURE_PTW)
>   
> -#if !defined(__ASSEMBLY__)
> -#ifdef CONFIG_HOTPLUG_CPU
> -void arch_unregister_cpu(int cpu);
> -#endif
> -#endif /* ! __ASSEMBLY__ */
> -
>   #endif /* _ASM_CPU_H */
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index f349c94510e8..91867a6a9f8e 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -24,7 +24,6 @@ static inline void prefill_possible_map(void) {}
>   #endif /* CONFIG_SMP */
>   
>   #ifdef CONFIG_HOTPLUG_CPU
> -extern void arch_unregister_cpu(int);
>   extern void soft_restart_cpu(void);
>   #endif
>   
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 677f963e02ce..c709747c4a18 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -531,7 +531,14 @@ int __weak arch_register_cpu(int cpu)
>   {
>   	return register_cpu(&per_cpu(cpu_devices, cpu), cpu);
>   }
> -#endif
> +
> +#ifdef CONFIG_HOTPLUG_CPU
> +void __weak arch_unregister_cpu(int num)
> +{
> +	unregister_cpu(&per_cpu(cpu_devices, num));
> +}
> +#endif /* CONFIG_HOTPLUG_CPU */
> +#endif /* CONFIG_GENERIC_CPU_DEVICES */
>   

It seems conflicting with its declaration in include/linux/cpu.h. Besides,
the function is still needed by drivers/acpi/acpi_processor.c::acpi_processor_make_not_present()
even both CONFIG_HOTPLUG_CPU and CONFIG_GENERIC_CPU_DEVICES are disabled?

>   static void __init cpu_dev_register_generic(void)
>   {

Thanks,
Gavin