Re: [PATCH RFC 13/22] arm64: setup: Switch over to GENERIC_CPU_DEVICES using arch_register_cpu()

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 07 Nov 2023 10:30:25 +0000
Russell King <rmk+kernel@armlinux.org.uk> wrote:

> From: James Morse <james.morse@arm.com>
> 
> To allow ACPI's _STA value to hide CPUs that are present, but not
> available to online right now due to VMM or firmware policy, the
> register_cpu() call needs to be made by the ACPI machinery when ACPI
> is in use. This allows it to hide CPUs that are unavailable from sysfs.
> 
> Switching to GENERIC_CPU_DEVICES is an intermediate step to allow all
> five ACPI architectures to be modified at once.
> 
> Switch over to GENERIC_CPU_DEVICES, and provide an arch_register_cpu()
> that populates the hotpluggable flag. arch_register_cpu() is also the
> interface the ACPI machinery expects.
> 
> The struct cpu in struct cpuinfo_arm64 is never used directly, remove
> it to use the one GENERIC_CPU_DEVICES provides.
> 
> This changes the CPUs visible in sysfs from possible to present, but
> on arm64 smp_prepare_cpus() ensures these are the same.
> 
> This patch also has the effect of moving the registration of CPUs from
> subsys to driver core initialisation, prior to any initcalls running.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

Given this series adds an arch_cpu_is_hotpluggable() callback we probably
want something in this patch description to say why this
isn't using that, but instead overriding arch_register_cpu()

Jonathan

> ---
> Changes since RFC v2:
>  * Add note about initialisation order change.
> ---
>  arch/arm64/Kconfig           |  1 +
>  arch/arm64/include/asm/cpu.h |  1 -
>  arch/arm64/kernel/setup.c    | 13 ++++---------
>  3 files changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7b071a00425d..84bce830e365 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -132,6 +132,7 @@ config ARM64
>  	select GENERIC_ARCH_TOPOLOGY
>  	select GENERIC_CLOCKEVENTS_BROADCAST
>  	select GENERIC_CPU_AUTOPROBE
> +	select GENERIC_CPU_DEVICES
>  	select GENERIC_CPU_VULNERABILITIES
>  	select GENERIC_EARLY_IOREMAP
>  	select GENERIC_IDLE_POLL_SETUP
> diff --git a/arch/arm64/include/asm/cpu.h b/arch/arm64/include/asm/cpu.h
> index f3034099fd95..b1e43f56ee46 100644
> --- a/arch/arm64/include/asm/cpu.h
> +++ b/arch/arm64/include/asm/cpu.h
> @@ -38,7 +38,6 @@ struct cpuinfo_32bit {
>  };
>  
>  struct cpuinfo_arm64 {
> -	struct cpu	cpu;
>  	struct kobject	kobj;
>  	u64		reg_ctr;
>  	u64		reg_cntfrq;
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 417a8a86b2db..165bd2c0dd5a 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -402,19 +402,14 @@ static inline bool cpu_can_disable(unsigned int cpu)
>  	return false;
>  }
>  
> -static int __init topology_init(void)
> +int arch_register_cpu(int num)
>  {
> -	int i;
> +	struct cpu *cpu = &per_cpu(cpu_devices, num);
>  
> -	for_each_possible_cpu(i) {
> -		struct cpu *cpu = &per_cpu(cpu_data.cpu, i);
> -		cpu->hotpluggable = cpu_can_disable(i);
> -		register_cpu(cpu, i);
> -	}
> +	cpu->hotpluggable = cpu_can_disable(num);
>  
> -	return 0;
> +	return register_cpu(cpu, num);
>  }
> -subsys_initcall(topology_init);
>  
>  static void dump_kernel_offset(void)
>  {