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SubjectRe: [PATCH v7 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()
On Thu, Apr 18, 2024 at 3:57 PM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> From: James Morse <james.morse@arm.com>
>
> The arm64 specific arch_register_cpu() call may defer CPU registration
> until the ACPI interpreter is available and the _STA method can
> be evaluated.
>
> If this occurs, then a second attempt is made in
> acpi_processor_get_info(). Note that the arm64 specific call has
> not yet been added so for now this will be called for the original
> hotplug case.
>
> For architectures that do not defer until the ACPI Processor
> driver loads (e.g. x86), for initially present CPUs there will
> already be a CPU device. If present do not try to register again.
>
> Systems can still be booted with 'acpi=off', or not include an
> ACPI description at all as in these cases arch_register_cpu()
> will not have deferred registration when first called.
>
> This moves the CPU register logic back to a subsys_initcall(),
> while the memory nodes will have been registered earlier.
> Note this is where the call was prior to the cleanup series so
> there should be no side effects of moving it back again for this
> specific case.
>
> [PATCH 00/21] Initial cleanups for vCPU HP.
> https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/
> commit 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
>
> 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>
> Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
> ---
> v7: Simplify the logic on whether to hotadd the CPU.
> This path can only be reached either for coldplug in which
> case all we care about is has register_cpu() already been
> called (identifying deferred), or hotplug in which case
> whether register_cpu() has been called is also sufficient.
> Checks on _STA related elements or the validity of the ID
> are no longer necessary here due to similar checks having
> moved elsewhere in the path.
> v6: Squash the two paths for conventional CPU Hotplug and arm64
> vCPU HP.
> ---
> drivers/acpi/acpi_processor.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 127ae8dcb787..4e65011e706c 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -350,14 +350,14 @@ static int acpi_processor_get_info(struct acpi_device *device)
> }
>
> /*
> - * Extra Processor objects may be enumerated on MP systems with
> - * less than the max # of CPUs. They should be ignored _iff
> - * they are physically not present.
> - *
> - * NOTE: Even if the processor has a cpuid, it may not be present
> - * because cpuid <-> apicid mapping is persistent now.
> + * This code is not called unless we know the CPU is present and
> + * enabled. The two paths are:
> + * a) Initially present CPUs on architectures that do not defer
> + * their arch_register_cpu() calls until this point.
> + * b) Hotplugged CPUs (enabled bit in _STA has transitioned from not
> + * enabled to enabled)
> */
> - if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> + if (!get_cpu_device(pr->id)) {
> ret = acpi_processor_hotadd_init(pr, device);

Yes, this is what I thought it should boil down to, so

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

>
> if (ret)
> --
> 2.39.2
>

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