Re: [PATCH v10 17/19] arm64: Kconfig: Enable hotplug CPU on arm64 if ACPI_PROCESSOR is enabled.

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Hi Jonathan and Catalin,

On 5/29/24 11:34 PM, Jonathan Cameron wrote:
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@xxxxxxxxxx>
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
---
  arch/arm64/Kconfig       |  1 +
  arch/arm64/kernel/acpi.c | 22 ++++++++++++++++++++++
  2 files changed, 23 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5d91259ee7b5..e8f2ef2312db 100644
--- a/arch/arm64/Kconfig
+++ b/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

ACPI_HOTPLUG_CPU depends on (ACPI_PROCESSOR && HOTPLUG_CPU). It needs to be:

	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR && HOTPLUG_CPU

Otherwise, we can have compiling error with the following configurations.

CONFIG_ACPI_PROCESSOR=y
CONFIG_HOTPLUG_CPU=n
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

Since the series has been queued to Catalin's "for-next/vcpu-hotplug" branch, I
guess the easiest way would be to fix it in place with Catalin's help.

Thanks,
Gavin

  	select ACPI_IORT if ACPI
  	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
  	select ACPI_MCFG if (ACPI && PCI)
diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index e0e7b93c16cc..9360ba86678b 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/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





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