drivers: base: add arch_cpu_is_hotpluggable()

The differences between architecture specific implementations of
arch_register_cpu() are down to whether the CPU is hotpluggable or not.
Rather than overriding the weak version of arch_register_cpu(), provide
a function that can be used to provide this detail instead.

Reviewed-by: Shaoqin Huang <[e-mail]>
Signed-off-by: "Russell King (Oracle)" <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Gavin Shan <[e-mail]>
Reviewed-by: Thomas Gleixner <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/cpu.c

···
 #ifdef CONFIG_GENERIC_CPU_DEVICES
 DEFINE_PER_CPU(struct cpu, cpu_devices);
 
+bool __weak arch_cpu_is_hotpluggable(int cpu)
+{
+	return false;
+}
+
 int __weak arch_register_cpu(int cpu)
 {
-	return register_cpu(&per_cpu(cpu_devices, cpu), cpu);
+	struct cpu *c = &per_cpu(cpu_devices, cpu);
+
+	c->hotpluggable = arch_cpu_is_hotpluggable(cpu);
+
+	return register_cpu(c, cpu);
 }
 
 #ifdef CONFIG_HOTPLUG_CPU

include/linux/cpu.h

···
 struct device *cpu_device_create(struct device *parent, void *drvdata,
 				 const struct attribute_group **groups,
 				 const char *fmt, ...);
+extern bool arch_cpu_is_hotpluggable(int cpu);
 extern int arch_register_cpu(int cpu);
 extern void arch_unregister_cpu(int cpu);
 #ifdef CONFIG_HOTPLUG_CPU