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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Mon, 18 Dec 2023 21:30:50 +0100
Message-ID: <CAJZ5v0je=-oVnSumZs=dzcyVuVUeVeTgO7yOnjGg1igyrS7EHQ@mail.gmail.com>
Subject: Re: [PATCH RFC v3 04/21] ACPI: processor: Register all CPUs from acpi_processor_get_info()
To: Russell King <rmk+kernel@armlinux.org.uk>
Cc: linux-pm@vger.kernel.org, loongarch@lists.linux.dev, 
	linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, 
	linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev, x86@kernel.org, 
	acpica-devel@lists.linuxfoundation.org, linux-csky@vger.kernel.org, 
	linux-doc@vger.kernel.org, linux-ia64@vger.kernel.org, 
	linux-parisc@vger.kernel.org, Salil Mehta <salil.mehta@huawei.com>, 
	Jean-Philippe Brucker <jean-philippe@linaro.org>, jianyong.wu@arm.com, justin.he@arm.com, 
	James Morse <james.morse@arm.com>
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On Wed, Dec 13, 2023 at 1:49=E2=80=AFPM Russell King <rmk+kernel@armlinux.o=
rg.uk> wrote:
>
> From: James Morse <james.morse@arm.com>
>
> To allow ACPI to skip the call to arch_register_cpu() when the _STA
> value indicates the CPU can't be brought online right now, move the
> arch_register_cpu() call into acpi_processor_get_info().

This kind of looks backwards to me and has a potential to become
super-confusing.

I would instead add a way for the generic code to ask the platform
firmware whether or not the given CPU is enabled and so it can be
registered.

> Systems can still be booted with 'acpi=3Doff', or not include an
> ACPI description at all. For these, the CPUs continue to be
> registered by cpu_dev_register_generic().
>
> This moves the CPU register logic back to a subsys_initcall(),
> while the memory nodes will have been registered earlier.

Isn't this somewhat risky?

> Signed-off-by: James Morse <james.morse@arm.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Miguel Luis <miguel.luis@oracle.com>
> Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> ---
> Changes since RFC v2:
>  * Fixup comment in acpi_processor_get_info() (Gavin Shan)
>  * Add comment in cpu_dev_register_generic() (Gavin Shan)
> ---
>  drivers/acpi/acpi_processor.c | 12 ++++++++++++
>  drivers/base/cpu.c            |  6 +++++-
>  2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.=
c
> index 0511f2bc10bc..e7ed4730cbbe 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -314,6 +314,18 @@ static int acpi_processor_get_info(struct acpi_devic=
e *device)
>                         cpufreq_add_device("acpi-cpufreq");
>         }
>
> +       /*
> +        * Register CPUs that are present. get_cpu_device() is used to sk=
ip
> +        * duplicate CPU descriptions from firmware.
> +        */
> +       if (!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> +           !get_cpu_device(pr->id)) {
> +               int ret =3D arch_register_cpu(pr->id);
> +
> +               if (ret)
> +                       return ret;
> +       }
> +
>         /*
>          *  Extra Processor objects may be enumerated on MP systems with
>          *  less than the max # of CPUs. They should be ignored _iff
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 47de0f140ba6..13d052bf13f4 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -553,7 +553,11 @@ static void __init cpu_dev_register_generic(void)
>  {
>         int i, ret;
>
> -       if (!IS_ENABLED(CONFIG_GENERIC_CPU_DEVICES))
> +       /*
> +        * When ACPI is enabled, CPUs are registered via
> +        * acpi_processor_get_info().
> +        */
> +       if (!IS_ENABLED(CONFIG_GENERIC_CPU_DEVICES) || !acpi_disabled)
>                 return;
>
>         for_each_present_cpu(i) {
> --
> 2.30.2
>
>