linux-kernel - Re: [RFC PATCH v2 23/35] ACPI: Warn when the present bit changes but the feature is not enabled

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Date:   Thu, 14 Sep 2023 15:32:07 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     James Morse <james.morse@....com>
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>, Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        <jianyong.wu@....com>, <justin.he@....com>
Subject: Re: [RFC PATCH v2 23/35] ACPI: Warn when the present bit changes
 but the feature is not enabled

On Wed, 13 Sep 2023 16:38:11 +0000
James Morse <james.morse@....com> wrote:

> ACPI firmware can trigger the events to add and remove CPUs, but the
> OS may not support this.
> 
> Print a warning when this happens.
> 
> This gives early warning on arm64 systems that don't support
> CONFIG_ACPI_HOTPLUG_PRESENT_CPU, as making CPUs not present has
> side effects for other parts of the system.
> 
> Signed-off-by: James Morse <james.morse@....com>
Seem like a good idea to me.

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

> ---
>  drivers/acpi/acpi_processor.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 2cafea1edc24..b67616079751 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -188,8 +188,10 @@ static int acpi_processor_make_present(struct acpi_processor *pr)
>  	acpi_status status;
>  	int ret;
>  
> -	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))
> +	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU)) {
> +		pr_err_once("Changing CPU present bit is not supported\n");
>  		return -ENODEV;
> +	}
>  
>  	if (invalid_phys_cpuid(pr->phys_id))
>  		return -ENODEV;
> @@ -462,8 +464,10 @@ static void acpi_processor_make_not_present(struct acpi_device *device)
>  {
>  	struct acpi_processor *pr;
>  
> -	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))
> +	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU)) {
> +		pr_err_once("Changing CPU present bit is not supported");
>  		return;
> +	}
>  
>  	pr = acpi_driver_data(device);
>  	if (pr->id >= nr_cpu_ids)