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

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Message-ID: <20231128151200.0000737c@Huawei.com>
Date:   Tue, 28 Nov 2023 15:12:00 +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 RFC 13/22] arm64: setup: Switch over to
 GENERIC_CPU_DEVICES using arch_register_cpu()

On Tue, 28 Nov 2023 15:08:54 +0000
Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:

> On Tue, 07 Nov 2023 10:30:25 +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>
> > Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.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()
> 
As per comment on next patch I'm fine with this slight dance.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>