[IA64] Simplify cpu_idle_wait

This is just Venki's patch[*] for x86 ported to ia64.

* http://marc.info/?l=linux-kernel&m=120249201318159&w=2

Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/process.c

@@ -52,7 +52,6 @@
 #include "sigframe.h"
 
 void (*ia64_mark_idle)(int);
-static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
 
 unsigned long boot_option_idle_override = 0;
 EXPORT_SYMBOL(boot_option_idle_override);
@@ -254,33 +253,23 @@ static inline void play_dead(void)
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
-void cpu_idle_wait(void)
+static void do_nothing(void *unused)
 {
-	unsigned int cpu, this_cpu = get_cpu();
-	cpumask_t map;
-	cpumask_t tmp = current->cpus_allowed;
-
-	set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
-	put_cpu();
-
-	cpus_clear(map);
-	for_each_online_cpu(cpu) {
-		per_cpu(cpu_idle_state, cpu) = 1;
-		cpu_set(cpu, map);
-	}
-
-	__get_cpu_var(cpu_idle_state) = 0;
+}
 
-	wmb();
-	do {
-		ssleep(1);
-		for_each_online_cpu(cpu) {
-			if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))
-				cpu_clear(cpu, map);
-		}
-		cpus_and(map, map, cpu_online_map);
-	} while (!cpus_empty(map));
-	set_cpus_allowed(current, tmp);
+/*
+ * cpu_idle_wait - Used to ensure that all the CPUs discard old value of
+ * pm_idle and update to new pm_idle value. Required while changing pm_idle
+ * handler on SMP systems.
+ *
+ * Caller must have changed pm_idle to the new value before the call. Old
+ * pm_idle value will not be used by any CPU after the return of this function.
+ */
+void cpu_idle_wait(void)
+{
+	smp_mb();
+	/* kick all the CPUs so that they exit out of pm_idle */
+	smp_call_function(do_nothing, NULL, 0, 1);
 }
 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 
@@ -308,9 +297,6 @@ cpu_idle (void)
 #ifdef CONFIG_SMP
 			min_xtp();
 #endif
-			if (__get_cpu_var(cpu_idle_state))
-				__get_cpu_var(cpu_idle_state) = 0;
-
 			rmb();
 			if (mark_idle)
 				(*mark_idle)(1);