Re: [PATCH RFC 07/22] drivers: base: Allow parts of GENERIC_CPU_DEVICES to be overridden

[Shaoqin Huang <shahuang@xxxxxxxxxx>]

On 11/7/23 18:29, Russell King (Oracle) wrote:
> From: James Morse <james.morse@xxxxxxx>
>
> 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.
>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
Reviewed-by: Shaoqin Huang <shahuang@xxxxxxxxxx>
> ---
> Changes since RFC:
>   * Dropped __init from x86/ia64 arch_register_cpu()
> Changes since RFC v2:
>   * Dropped unnecessary Loongarch asm/cpu.h changes
> ---
>   drivers/base/cpu.c  | 14 ++++++++++----
>   include/linux/cpu.h |  4 ++++
>   2 files changed, 14 insertions(+), 4 deletions(-)
>
> 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 fc8094419084..1e982d63eae8 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -88,6 +88,10 @@ 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

--
Shaoqin