linux-kernel - Re: [PATCH 12/21] arm64: setup: Switch over to GENERIC_CPU_DEVICES using arch_register

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Message-ID: <20231211132054.GC25681@willie-the-truck>
Date:   Mon, 11 Dec 2023 13:20:55 +0000
From:   Will Deacon <will@...nel.org>
To:     Russell King <rmk+kernel@...linux.org.uk>
Cc:     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, 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>
Subject: Re: [PATCH 12/21] arm64: setup: Switch over to GENERIC_CPU_DEVICES
 using arch_register_cpu()

On Tue, Nov 21, 2023 at 01:44:51PM +0000, Russell King 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>
> Reviewed-by: Shaoqin Huang <shahuang@...hat.com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> ---
> 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(-)

Acked-by: Will Deacon <will@...nel.org>

Will