arm64: Kconfig: Enable hotplug CPU on arm64 if ACPI_PROCESSOR is enabled.

In order to move arch_register_cpu() to be called via the same path
for initially present CPUs described by ACPI and hotplugged CPUs
ACPI_HOTPLUG_CPU needs to be enabled.

The protection against invalid IDs in acpi_map_cpu() is needed as
at least one production BIOS is in the wild which reports entries
in DSDT (with no _STA method, so assumed enabled and present)
that don't match MADT.
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20240529133446.28446-18-Jonathan.Cameron@huawei.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

@@ -5,6 +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_IORT if ACPI
 	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
 	select ACPI_MCFG if (ACPI && PCI)

arch/arm64/kernel/acpi.c

@@ -30,6 +30,7 @@
 #include <linux/pgtable.h>
 
 #include <acpi/ghes.h>
+#include <acpi/processor.h>
 #include <asm/cputype.h>
 #include <asm/cpu_ops.h>
 #include <asm/daifflags.h>
@@ -423,6 +424,27 @@ void arch_reserve_mem_area(acpi_physical_address addr, size_t size)
 	memblock_mark_nomap(addr, size);
 }
 
+#ifdef CONFIG_ACPI_HOTPLUG_CPU
+int acpi_map_cpu(acpi_handle handle, phys_cpuid_t physid, u32 apci_id,
+		 int *pcpu)
+{
+	/* If an error code is passed in this stub can't fix it */
+	if (*pcpu < 0) {
+		pr_warn_once("Unable to map CPU to valid ID\n");
+		return *pcpu;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(acpi_map_cpu);
+
+int acpi_unmap_cpu(int cpu)
+{
+	return 0;
+}
+EXPORT_SYMBOL(acpi_unmap_cpu);
+#endif /* CONFIG_ACPI_HOTPLUG_CPU */
+
 #ifdef CONFIG_ACPI_FFH
 /*
  * Implements ARM64 specific callbacks to support ACPI FFH Operation Region as