arm64: hw_breakpoint: convert CPU hotplug notifier to new infrastructure

The arm64 hw_breakpoint implementation uses a CPU hotplug notifier to
reset the {break,watch}point registers when CPUs come online.

This patch converts the code to the new hotplug mechanism, whilst moving
the invocation earlier to remove the need to disable IRQs explicitly in
the driver (which could cause havok if we trip a watchpoint in an IRQ
handler whilst restoring the debug register state).

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/suspend.c

@@ -23,8 +23,8 @@ unsigned long *sleep_save_stash;
  * time the notifier runs debug exceptions might have been enabled already,
  * with HW breakpoints registers content still in an unknown state.
  */
-static void (*hw_breakpoint_restore)(void *);
-void __init cpu_suspend_set_dbg_restorer(void (*hw_bp_restore)(void *))
+static int (*hw_breakpoint_restore)(unsigned int);
+void __init cpu_suspend_set_dbg_restorer(int (*hw_bp_restore)(unsigned int))
 {
 	/* Prevent multiple restore hook initializations */
 	if (WARN_ON(hw_breakpoint_restore))
@@ -34,6 +34,8 @@ void __init cpu_suspend_set_dbg_restorer(void (*hw_bp_restore)(void *))
 
 void notrace __cpu_suspend_exit(void)
 {
+	unsigned int cpu = smp_processor_id();
+
 	/*
 	 * We are resuming from reset with the idmap active in TTBR0_EL1.
 	 * We must uninstall the idmap and restore the expected MMU
@@ -45,7 +47,7 @@ void notrace __cpu_suspend_exit(void)
 	 * Restore per-cpu offset before any kernel
 	 * subsystem relying on it has a chance to run.
 	 */
-	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
+	set_my_cpu_offset(per_cpu_offset(cpu));
 
 	/*
 	 * Restore HW breakpoint registers to sane values
@@ -53,7 +55,7 @@ void notrace __cpu_suspend_exit(void)
 	 * through local_dbg_restore.
 	 */
 	if (hw_breakpoint_restore)
-		hw_breakpoint_restore(NULL);
+		hw_breakpoint_restore(cpu);
 }
 
 /*