cpuidle: use last_state which can reflect the actual state entered

cpuidle accounts the idle time for the C-state it was trying to enter and
not to the actual state that the driver eventually entered. The driver may
select a different state than the one chosen by cpuidle due to
constraints like bus-mastering, etc.

Change the time acounting code to look at the dev->last_state after
returning from target_state->enter(). Driver can modify dev->last_state
internally, inside the enter routine to reflect the actual C-state
entered.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Tested-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/cpuidle/cpuidle.c

@@ -67,8 +67,11 @@ static void cpuidle_idle_call(void)
 	target_state = &dev->states[next_state];
 
 	/* enter the state and update stats */
-	dev->last_residency = target_state->enter(dev, target_state);
 	dev->last_state = target_state;
+	dev->last_residency = target_state->enter(dev, target_state);
+	if (dev->last_state)
+		target_state = dev->last_state;
+
 	target_state->time += (unsigned long long)dev->last_residency;
 	target_state->usage++;