ARM: clean up idle handlers

Let's factor out the need_resched() check instead of having it duplicated
in every pm_idle implementations to avoid inconsistencies (omap2_pm_idle
is missing it already).

The forceful re-enablement of IRQs after pm_idle has returned can go.
The warning certainly doesn't trigger for existing users.

To get rid of the pm_idle calling convention oddity, let's introduce
arm_pm_idle() allowing for the local_irq_enable() to be factored out
from SOC specific implementations. The default pm_idle function becomes
a wrapper for arm_pm_idle and it takes care of enabling IRQs closer to
where they are initially disabled.

And finally move the comment explaining the reason for that turning off
of IRQs to a more proper location.
Signed-off-by: NNicolas Pitre <nicolas.pitre@linaro.org>
Acked-and-tested-by: NJamie Iles <jamie@jamieiles.com>

arch/arm/include/asm/system.h

@@ -110,6 +110,7 @@ extern void cpu_init(void);
 
 void soft_restart(unsigned long);
 extern void (*arm_pm_restart)(char str, const char *cmd);
+extern void (*arm_pm_idle)(void);
 
 #define UDBG_UNDEFINED	(1 << 0)
 #define UDBG_SYSCALL	(1 << 1)

arch/arm/kernel/process.c

@@ -181,12 +181,16 @@ void cpu_idle_wait(void)
 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 
 /*
- * This is our default idle handler.  We need to disable
- * interrupts here to ensure we don't miss a wakeup call.
+ * This is our default idle handler.
  */
+
+void (*arm_pm_idle)(void);
+
 static void default_idle(void)
 {
-	if (!need_resched())
+	if (arm_pm_idle)
+		arm_pm_idle();
+	else
 		arch_idle();
 	local_irq_enable();
 }
@@ -215,6 +219,10 @@ void cpu_idle(void)
 				cpu_die();
 #endif
 
+			/*
+			 * We need to disable interrupts here
+			 * to ensure we don't miss a wakeup call.
+			 */
 			local_irq_disable();
 #ifdef CONFIG_PL310_ERRATA_769419
 			wmb();
@@ -222,20 +230,19 @@ void cpu_idle(void)
 			if (hlt_counter) {
 				local_irq_enable();
 				cpu_relax();
-			} else {
+			} else if (!need_resched()) {
 				stop_critical_timings();
 				if (cpuidle_idle_call())
 					pm_idle();
 				start_critical_timings();
 				/*
-				 * This will eventually be removed - pm_idle
-				 * functions should always return with IRQs
-				 * enabled.
+				 * pm_idle functions must always
+				 * return with IRQs enabled.
 				 */
 				WARN_ON(irqs_disabled());
+			} else
 				local_irq_enable();
 		}
-		}
 		leds_event(led_idle_end);
 		rcu_idle_exit();
 		tick_nohz_idle_exit();