[PATCH 07/21] drivers: base: Allow parts of GENERIC_CPU_DEVICES to be overridden

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From: James Morse <james.morse@xxxxxxx>

Architectures often have extra per-cpu work that needs doing
before a CPU is registered, often to determine if a CPU is

To allow the ACPI architectures to use GENERIC_CPU_DEVICES, move
the cpu_register() call into arch_register_cpu(), which is made __weak
so architectures with extra work can override it.
This aligns with the way x86, ia64 and loongarch register hotplug CPUs
when they become present.

Signed-off-by: James Morse <james.morse@xxxxxxx>
Reviewed-by: Shaoqin Huang <shahuang@xxxxxxxxxx>
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
Changes since RFC:
 * Dropped __init from x86/ia64 arch_register_cpu()
Changes since RFC v2:
 * Dropped unnecessary Loongarch asm/cpu.h changes
 drivers/base/cpu.c  | 14 ++++++++++----
 include/linux/cpu.h |  4 ++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 34b48f660b6b..579064fda97b 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -525,19 +525,25 @@ bool cpu_is_hotpluggable(unsigned int cpu)
-static DEFINE_PER_CPU(struct cpu, cpu_devices);
+DEFINE_PER_CPU(struct cpu, cpu_devices);
+int __weak arch_register_cpu(int cpu)
+	return register_cpu(&per_cpu(cpu_devices, cpu), cpu);
 static void __init cpu_dev_register_generic(void)
 	int i;
+		return;
 	for_each_present_cpu(i) {
-		if (register_cpu(&per_cpu(cpu_devices, i), i))
+		if (arch_register_cpu(i))
 			panic("Failed to register CPU device");
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index fc8094419084..1e982d63eae8 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -88,6 +88,10 @@ extern ssize_t arch_cpu_probe(const char *, size_t);
 extern ssize_t arch_cpu_release(const char *, size_t);
+DECLARE_PER_CPU(struct cpu, cpu_devices);
  * These states are not related to the core CPU hotplug mechanism. They are
  * used by various (sub)architectures to track internal state

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