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

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Date:   Thu, 30 Nov 2023 16:54:06 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
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>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 12/21] arm64: setup: Switch over to GENERIC_CPU_DEVICES
 using arch_register_cpu()

On Tue, 21 Nov 2023 13:44:51 +0000
Russell King <rmk+kernel@...linux.org.uk> 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>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>