Both ACPI_PROCESSOR and HOTPLUG_CPU are needed by ACPI_HOTPLUG_CPU.
Otherwise, we can have compiling error with the following configurations.

  CONFIG_HOTPLUG_CPU=n
  CONFIG_ACPI_PROCESSOR=y
  CONFIG_ACPI_HOTPLUG_CPU=y

  arch/arm64/kernel/smp.c: In function ‘arch_unregister_cpu’:
  arch/arm64/kernel/smp.c:563:9: error: implicit declaration of  \
  function ‘unregister_cpu’; did you mean ‘register_cpu’?        \
  [-Werror=implicit-function-declaration]
  563 |         unregister_cpu(c);
      |         ^~~~~~~~~~~~~~
      |         register_cpu

Fix it by enabling ACPI_HOTPLUG_CPU when both ACPI_PROCESSOR and
HOTPLUG_CPU are enabled, consistent with other architectures like
x86 and loongarch.

Fixes: 9d0873892f4d ("arm64: Kconfig: Enable hotplug CPU on arm64 if ACPI_PROCESSOR is enabled.")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202406300437.XnuW0n34-lkp@intel.com/
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 arch/arm64/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index e8f2ef2312db..ff17c5705324 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -5,7 +5,7 @@ config ARM64
 	select ACPI_CCA_REQUIRED if ACPI
 	select ACPI_GENERIC_GSI if ACPI
 	select ACPI_GTDT if ACPI
-	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR
+	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR && HOTPLUG_CPU
 	select ACPI_IORT if ACPI
 	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
 	select ACPI_MCFG if (ACPI && PCI)
-- 
2.45.1

On Mon, 01 Jul 2024 10:11:32 +1000, Gavin Shan wrote:
> Both ACPI_PROCESSOR and HOTPLUG_CPU are needed by ACPI_HOTPLUG_CPU.
> Otherwise, we can have compiling error with the following configurations.
> 
>   CONFIG_HOTPLUG_CPU=n
>   CONFIG_ACPI_PROCESSOR=y
>   CONFIG_ACPI_HOTPLUG_CPU=y
> 
> [...]

Applied to arm64 (for-next/vcpu-hotplug), thanks!

[1/1] arm64: Kconfig: Fix dependencies to enable ACPI_HOTPLUG_CPU
      https://git.kernel.org/arm64/c/46800e38ef0e

-- 
Catalin

On Mon,  1 Jul 2024 10:11:32 +1000
Gavin Shan <gshan@redhat.com> wrote:

> Both ACPI_PROCESSOR and HOTPLUG_CPU are needed by ACPI_HOTPLUG_CPU.
> Otherwise, we can have compiling error with the following configurations.
> 
>   CONFIG_HOTPLUG_CPU=n
>   CONFIG_ACPI_PROCESSOR=y
>   CONFIG_ACPI_HOTPLUG_CPU=y
> 
>   arch/arm64/kernel/smp.c: In function ‘arch_unregister_cpu’:
>   arch/arm64/kernel/smp.c:563:9: error: implicit declaration of  \
>   function ‘unregister_cpu’; did you mean ‘register_cpu’?        \
>   [-Werror=implicit-function-declaration]
>   563 |         unregister_cpu(c);
>       |         ^~~~~~~~~~~~~~
>       |         register_cpu
> 
> Fix it by enabling ACPI_HOTPLUG_CPU when both ACPI_PROCESSOR and
> HOTPLUG_CPU are enabled, consistent with other architectures like
> x86 and loongarch.
> 
> Fixes: 9d0873892f4d ("arm64: Kconfig: Enable hotplug CPU on arm64 if ACPI_PROCESSOR is enabled.")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202406300437.XnuW0n34-lkp@intel.com/
> Signed-off-by: Gavin Shan <gshan@redhat.com>

Thanks for the quick analysis and patch!

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
>  arch/arm64/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index e8f2ef2312db..ff17c5705324 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -5,7 +5,7 @@ config ARM64
>  	select ACPI_CCA_REQUIRED if ACPI
>  	select ACPI_GENERIC_GSI if ACPI
>  	select ACPI_GTDT if ACPI
> -	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR
> +	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR && HOTPLUG_CPU
>  	select ACPI_IORT if ACPI
>  	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
>  	select ACPI_MCFG if (ACPI && PCI)