arm64: setup: Switch over to GENERIC_CPU_DEVICES using arch_register_cpu()

To allow ACPI's _STA value to hide CPUs that are present, but not
available to online right now due to VMM or firmware policy, the
register_cpu() call needs to be made by the ACPI machinery when ACPI
is in use. This allows it to hide CPUs that are unavailable from sysfs.

Switching to GENERIC_CPU_DEVICES is an intermediate step to allow all
five ACPI architectures to be modified at once.

Switch over to GENERIC_CPU_DEVICES, and provide an arch_register_cpu()
that populates the hotpluggable flag. arch_register_cpu() is also the
interface the ACPI machinery expects.

The struct cpu in struct cpuinfo_arm64 is never used directly, remove
it to use the one GENERIC_CPU_DEVICES provides.

This changes the CPUs visible in sysfs from possible to present, but
on arm64 smp_prepare_cpus() ensures these are the same.

This patch also has the effect of moving the registration of CPUs from
subsys to driver core initialisation, prior to any initcalls running.
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/E1r5R3b-00Csza-Ku@rmk-PC.armlinux.org.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm64/Kconfig

@@ -132,6 +132,7 @@ config ARM64
 	select GENERIC_ARCH_TOPOLOGY
 	select GENERIC_CLOCKEVENTS_BROADCAST
 	select GENERIC_CPU_AUTOPROBE
+	select GENERIC_CPU_DEVICES
 	select GENERIC_CPU_VULNERABILITIES
 	select GENERIC_EARLY_IOREMAP
 	select GENERIC_IDLE_POLL_SETUP

arch/arm64/include/asm/cpu.h

@@ -38,7 +38,6 @@ struct cpuinfo_32bit {
 };
 
 struct cpuinfo_arm64 {
-	struct cpu	cpu;
 	struct kobject	kobj;
 	u64		reg_ctr;
 	u64		reg_cntfrq;

arch/arm64/kernel/setup.c

@@ -402,19 +402,14 @@ static inline bool cpu_can_disable(unsigned int cpu)
 	return false;
 }
 
-static int __init topology_init(void)
+int arch_register_cpu(int num)
 {
-	int i;
+	struct cpu *cpu = &per_cpu(cpu_devices, num);
 
-	for_each_possible_cpu(i) {
-		struct cpu *cpu = &per_cpu(cpu_data.cpu, i);
-		cpu->hotpluggable = cpu_can_disable(i);
-		register_cpu(cpu, i);
-	}
+	cpu->hotpluggable = cpu_can_disable(num);
 
-	return 0;
+	return register_cpu(cpu, num);
 }
-subsys_initcall(topology_init);
 
 static void dump_kernel_offset(void)
 {