Re: [PATCH RFC v3 04/21] ACPI: processor: Register all CPUs from acpi_processor_get_info()

Rafael J. Wysocki
2023-12-18T20:31:01Z

On Wed, Dec 13, 2023 at 1:49 PM Russell King <rmk+kernel@armlinux.org.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=off', 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_device *device)
> cpufreq_add_device("acpi-cpufreq");
> }
>
> + /*
> + * Register CPUs that are present. get_cpu_device() is used to skip
> + * duplicate CPU descriptions from firmware.
> + */
> + if (!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> + !get_cpu_device(pr->id)) {
> + int ret = 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
>
>