On Wed, 13 Sep 2023 16:37:51 +0000
James Morse <james.morse@xxxxxxx> wrote:
> Architectures often have extra per-cpu work that needs doing
> before a CPU is registered, often to determine if a CPU is
> hotpluggable.
>
> To allow the ACPI architectures to use GENERIC_CPU_DEVICES, move
> the cpu_register() call into arch_register_cpu(), which is made __weak
> so architectures with extra work can override it.
> This aligns with the way x86, ia64 and loongarch register hotplug CPUs
> when they become present.
Perhaps call out that you are also making cpu_devices visible outside
of base/cpu.c
Note it isn't obvious to me why you do that in this patch. I assume
it will be needed later...
Otherwise seems sensible to me.
>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ---
> Changes since RFC:
> * Dropped __init from x86/ia64 arch_register_cpu()
> ---
> arch/ia64/include/asm/cpu.h | 1 -
> arch/ia64/kernel/topology.c | 2 +-
> arch/loongarch/include/asm/cpu.h | 1 -
> arch/x86/include/asm/cpu.h | 1 -
> arch/x86/kernel/topology.c | 2 +-
> drivers/base/cpu.c | 14 ++++++++++----
> include/linux/cpu.h | 5 +++++
> 7 files changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/arch/ia64/include/asm/cpu.h b/arch/ia64/include/asm/cpu.h
> index db125df9e088..a3e690e685e5 100644
> --- a/arch/ia64/include/asm/cpu.h
> +++ b/arch/ia64/include/asm/cpu.h
> @@ -16,7 +16,6 @@ DECLARE_PER_CPU(struct ia64_cpu, cpu_devices);
> DECLARE_PER_CPU(int, cpu_state);
>
> #ifdef CONFIG_HOTPLUG_CPU
> -extern int arch_register_cpu(int num);
> extern void arch_unregister_cpu(int);
> #endif
>
> diff --git a/arch/ia64/kernel/topology.c b/arch/ia64/kernel/topology.c
> index 94a848b06f15..741863a187a6 100644
> --- a/arch/ia64/kernel/topology.c
> +++ b/arch/ia64/kernel/topology.c
> @@ -59,7 +59,7 @@ void __ref arch_unregister_cpu(int num)
> }
> EXPORT_SYMBOL(arch_unregister_cpu);
> #else
> -static int __init arch_register_cpu(int num)
> +int __init arch_register_cpu(int num)
> {
> return register_cpu(&sysfs_cpus[num].cpu, num);
> }
> diff --git a/arch/loongarch/include/asm/cpu.h b/arch/loongarch/include/asm/cpu.h
> index 7afe8cbb844e..b8568e637420 100644
> --- a/arch/loongarch/include/asm/cpu.h
> +++ b/arch/loongarch/include/asm/cpu.h
> @@ -130,7 +130,6 @@ enum cpu_type_enum {
>
> #if !defined(__ASSEMBLY__)
> #ifdef CONFIG_HOTPLUG_CPU
> -int arch_register_cpu(int num);
> void arch_unregister_cpu(int cpu);
> #endif
> #endif /* ! __ASSEMBLY__ */
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index 3a233ebff712..96dc4665e87d 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -28,7 +28,6 @@ struct x86_cpu {
> };
>
> #ifdef CONFIG_HOTPLUG_CPU
> -extern int arch_register_cpu(int num);
> extern void arch_unregister_cpu(int);
> extern void soft_restart_cpu(void);
> #endif
> diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
> index ca004e2e4469..0bab03130033 100644
> --- a/arch/x86/kernel/topology.c
> +++ b/arch/x86/kernel/topology.c
> @@ -54,7 +54,7 @@ void arch_unregister_cpu(int num)
> EXPORT_SYMBOL(arch_unregister_cpu);
> #else /* CONFIG_HOTPLUG_CPU */
>
> -static int __init arch_register_cpu(int num)
> +int __init arch_register_cpu(int num)
> {
> return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
> }
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 34b48f660b6b..579064fda97b 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -525,19 +525,25 @@ bool cpu_is_hotpluggable(unsigned int cpu)
> EXPORT_SYMBOL_GPL(cpu_is_hotpluggable);
>
> #ifdef CONFIG_GENERIC_CPU_DEVICES
> -static DEFINE_PER_CPU(struct cpu, cpu_devices);
> +DEFINE_PER_CPU(struct cpu, cpu_devices);
> +
> +int __weak arch_register_cpu(int cpu)
> +{
> + return register_cpu(&per_cpu(cpu_devices, cpu), cpu);
> +}
> #endif
>
> static void __init cpu_dev_register_generic(void)
> {
> -#ifdef CONFIG_GENERIC_CPU_DEVICES
> int i;
>
> + if (!IS_ENABLED(CONFIG_GENERIC_CPU_DEVICES))
> + return;
> +
> for_each_present_cpu(i) {
> - if (register_cpu(&per_cpu(cpu_devices, i), i))
> + if (arch_register_cpu(i))
> panic("Failed to register CPU device");
> }
> -#endif
> }
>
> #ifdef CONFIG_GENERIC_CPU_VULNERABILITIES
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 0abd60a7987b..a71691d7c2ca 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -80,12 +80,17 @@ extern __printf(4, 5)
> struct device *cpu_device_create(struct device *parent, void *drvdata,
> const struct attribute_group **groups,
> const char *fmt, ...);
> +extern int arch_register_cpu(int cpu);
> #ifdef CONFIG_HOTPLUG_CPU
> extern void unregister_cpu(struct cpu *cpu);
> extern ssize_t arch_cpu_probe(const char *, size_t);
> extern ssize_t arch_cpu_release(const char *, size_t);
> #endif
>
> +#ifdef CONFIG_GENERIC_CPU_DEVICES
> +DECLARE_PER_CPU(struct cpu, cpu_devices);
> +#endif
> +
> /*
> * These states are not related to the core CPU hotplug mechanism. They are
> * used by various (sub)architectures to track internal state
