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    SubjectRe: [RFC PATCH v2 24/35] drivers: base: Implement weak arch_unregister_cpu()
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    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@linaro.org>
    > Signed-off-by: James Morse <james.morse@arm.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

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