linux-kernel - Re: [PATCH RFC 13/22] arm64: setup: Switch over to GENERIC_CPU_DEVICES using arch_register

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Message-ID: <7e7f37c9-c364-7749-c700-8bc29ac0c5d1@redhat.com>
Date:   Fri, 10 Nov 2023 11:36:47 +0800
From:   Shaoqin Huang <shahuang@...hat.com>
To:     "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        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,
        x86@...nel.org, linux-csky@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-parisc@...r.kernel.org
Cc:     Salil Mehta <salil.mehta@...wei.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com,
        James Morse <james.morse@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH RFC 13/22] arm64: setup: Switch over to
 GENERIC_CPU_DEVICES using arch_register_cpu()



On 11/7/23 18:30, Russell King (Oracle) wrote:
> From: James Morse <james.morse@....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@....com>
> Reviewed-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
Reviewed-by: Shaoqin Huang <shahuang@...hat.com>
> ---
> 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)
>   {

-- 
Shaoqin