arm64: debug: convert OS lock CPU hotplug notifier to new infrastructure

The arm64 debug monitor initialisation code uses a CPU hotplug notifier
to clear the OS lock when CPUs come online.

This patch converts the code to the new hotplug mechanism.

Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/debug-monitors.c

@@ -132,36 +132,18 @@ NOKPROBE_SYMBOL(disable_debug_monitors);
 /*
  * OS lock clearing.
  */
-static void clear_os_lock(void *unused)
+static int clear_os_lock(unsigned int cpu)
 {
 	asm volatile("msr oslar_el1, %0" : : "r" (0));
+	isb();
+	return 0;
 }
 
-static int os_lock_notify(struct notifier_block *self,
-				    unsigned long action, void *data)
-{
-	if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
-		clear_os_lock(NULL);
-	return NOTIFY_OK;
-}
-
-static struct notifier_block os_lock_nb = {
-	.notifier_call = os_lock_notify,
-};
-
 static int debug_monitors_init(void)
 {
-	cpu_notifier_register_begin();
-
-	/* Clear the OS lock. */
-	on_each_cpu(clear_os_lock, NULL, 1);
-	isb();
-
-	/* Register hotplug handler. */
-	__register_cpu_notifier(&os_lock_nb);
-
-	cpu_notifier_register_done();
-	return 0;
+	return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
+				 "CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING",
+				 clear_os_lock, NULL);
 }
 postcore_initcall(debug_monitors_init);
 

include/linux/cpuhotplug.h

@@ -45,6 +45,7 @@ enum cpuhp_state {
 	CPUHP_AP_PERF_METAG_STARTING,
 	CPUHP_AP_MIPS_OP_LOONGSON3_STARTING,
 	CPUHP_AP_ARM_VFP_STARTING,
+	CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
 	CPUHP_AP_PERF_ARM_HW_BREAKPOINT_STARTING,
 	CPUHP_AP_PERF_ARM_STARTING,
 	CPUHP_AP_ARM_L2X0_STARTING,