[PATCH RFC 05/22] ACPI: Move ACPI_HOTPLUG_CPU to be disabled on arm64 and riscv

[Gavin Shan]

On 11/7/23 20:29, Russell King (Oracle) wrote:
> From: James Morse <james.morse at arm.com>
> 
> Neither arm64 nor riscv support physical hotadd of CPUs that were not
> present at boot. For arm64 much of the platform description is in static
> tables which do not have update methods. arm64 does support HOTPLUG_CPU,
> which is backed by a firmware interface to turn CPUs on and off.
> 
> acpi_processor_hotadd_init() and acpi_processor_remove() are for adding
> and removing CPUs that were not present at boot. arm64 systems that do this
> are not supported as there is currently insufficient information in the
> platform description. (e.g. did the GICR get removed too?)
> 
> arm64 currently relies on the MADT enabled flag check in map_gicc_mpidr()
> to prevent CPUs that were not described as present at boot from being
> added to the system. Similarly, riscv relies on the same check in
> map_rintc_hartid(). Both architectures also rely on the weak 'always fails'
> definitions of acpi_map_cpu() and arch_register_cpu().
> 
> Subsequent changes will redefine ACPI_HOTPLUG_CPU as making possible
> CPUs present. Neither arm64 nor riscv support this.
> 
> Disable ACPI_HOTPLUG_CPU for arm64 and riscv by removing 'default y' and
> selecting it on the other three ACPI architectures. This allows the weak
> definitions of some symbols to be removed.
> 
> Signed-off-by: James Morse <james.morse at arm.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
> ---
> Changes since RFC:
>   * Expanded conditions to avoid ACPI_HOTPLUG_CPU being enabled when
>     HOTPLUG_CPU isn't.
> Changes since RFC v3:
>   * Dropped ia64 changes
> ---
>   arch/loongarch/Kconfig        |  1 +
>   arch/x86/Kconfig              |  1 +
>   drivers/acpi/Kconfig          |  1 -
>   drivers/acpi/acpi_processor.c | 18 ------------------
>   4 files changed, 2 insertions(+), 19 deletions(-)
> 

With the following nits addressed:

Reviewed-by: Gavin Shan <gshan at redhat.com>

> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index d889a0b97bc1..64620e90c12c 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -5,6 +5,7 @@ config LOONGARCH
>   	select ACPI
>   	select ACPI_GENERIC_GSI if ACPI
>   	select ACPI_MCFG if ACPI
> +	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR && HOTPLUG_CPU
>   	select ACPI_PPTT if ACPI
>   	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
>   	select ARCH_BINFMT_ELF_STATE
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 3762f41bb092..dbdcfc708369 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -59,6 +59,7 @@ config X86
>   	#
>   	select ACPI_LEGACY_TABLES_LOOKUP	if ACPI
>   	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
> +	select ACPI_HOTPLUG_CPU			if ACPI_PROCESSOR && HOTPLUG_CPU
>   	select ARCH_32BIT_OFF_T			if X86_32
>   	select ARCH_CLOCKSOURCE_INIT
>   	select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index f819e760ff19..a3acfc750fce 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -310,7 +310,6 @@ config ACPI_HOTPLUG_CPU
>   	bool
>   	depends on ACPI_PROCESSOR && HOTPLUG_CPU
>   	select ACPI_CONTAINER
> -	default y
>   
>   config ACPI_PROCESSOR_AGGREGATOR
>   	tristate "Processor Aggregator"
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 0f5218e361df..4fe2ef54088c 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -184,24 +184,6 @@ static void __init acpi_pcc_cpufreq_init(void) {}
>   
>   /* Initialization */
>   #ifdef CONFIG_ACPI_HOTPLUG_CPU
> -int __weak acpi_map_cpu(acpi_handle handle,
> -		phys_cpuid_t physid, u32 acpi_id, int *pcpu)
> -{
> -	return -ENODEV;
> -}
> -
> -int __weak acpi_unmap_cpu(int cpu)
> -{
> -	return -ENODEV;
> -}
> -
> -int __weak arch_register_cpu(int cpu)
> -{
> -	return -ENODEV;
> -}
> -
> -void __weak arch_unregister_cpu(int cpu) {}
> -

Since we're here, EXPORT_SYMBOL() can be dropped for these functions on
x86 and loongarch because they're not called from a module?

>   static int acpi_processor_hotadd_init(struct acpi_processor *pr)
>   {
>   	unsigned long long sta;

Thanks,
Gavin