ACPI: Move ACPI_HOTPLUG_CPU to be enabled per architecture

arm64 doesn't support physical hotadd of CPUs that were not present at boot.
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. Adding support for virtual CPU hotplug (where the
vCPUs have been present the whole time) would require this check to be
removed, possibly allowing physical CPUs to be added.

Disable ACPI_HOTPLUG_CPU for arm64 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@arm.com>
---
Changes since RFC:
 * Expanded x86 conditions to avoid ACPI_HOTPLUG_CPU being enabled when
   HOTPLUG_CPU isn't.

6 files changed, 10 insertions, 19 deletions

diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 2cd93e6bf0fe..16596c98729e 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -16,6 +16,7 @@ config IA64
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_MIGHT_HAVE_PC_SERIO
 	select ACPI
+	select ACPI_HOTPLUG_CPU if ACPI
 	select ACPI_NUMA if NUMA
 	select ARCH_ENABLE_MEMORY_HOTPLUG
 	select ARCH_ENABLE_MEMORY_HOTREMOVE
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 465759f6b0ed..3ec2ed070409 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -4,6 +4,7 @@ config LOONGARCH
 	default y
 	select ACPI
 	select ACPI_GENERIC_GSI if ACPI
+	select ACPI_HOTPLUG_CPU if ACPI
 	select ACPI_MCFG if ACPI
 	select ACPI_PPTT if ACPI
 	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
diff --git a/arch/loongarch/include/asm/cpu.h b/arch/loongarch/include/asm/cpu.h
index 48b9f7168bcc..9be65d86aba6 100644
--- a/arch/loongarch/include/asm/cpu.h
+++ b/arch/loongarch/include/asm/cpu.h
@@ -128,4 +128,11 @@ enum cpu_type_enum {
 #define LOONGARCH_CPU_HYPERVISOR	BIT_ULL(CPU_FEATURE_HYPERVISOR)
 #define LOONGARCH_CPU_PTW		BIT_ULL(CPU_FEATURE_PTW)
 
+#if !defined(__ASSEMBLY__)
+#ifdef CONFIG_HOTPLUG_CPU
+extern int arch_register_cpu(int num);
+extern void arch_unregister_cpu(int);
+#endif
+#endif /* ! __ASSEMBLY__ */
+
 #endif /* _ASM_CPU_H */
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e36261b4ea14..95e3c37cd3af 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -60,6 +60,7 @@ config X86
 	#
 	select ACPI_LEGACY_TABLES_LOOKUP	if ACPI
 	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
+	select ACPI_HOTPLUG_CPU			if ACPI && 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 00dd309b6682..16689b73f820 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -309,7 +309,6 @@ 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 f9aa02cac6d1..85b91b748edc 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -179,24 +179,6 @@ 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) {}
-
 static int acpi_processor_hotadd_init(struct acpi_processor *pr)
 {
 	unsigned long long sta;