cpuidle / menu: Return (-1) if there are no suitable states

commit 3836785a upstream.

If there is a PM QoS latency limit and all of the sufficiently shallow
C-states are disabled, the cpuidle menu governor returns 0 which on
some systems is CPUIDLE_DRIVER_STATE_START and shouldn't be returned
if that C-state has been disabled.

Fix the issue by modifying the menu governor to return (-1) in such
situations.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
[shilpab: Backport to 3.10.y
 - adjust context
 - add a check if 'next_state' is less than 0 in 'cpuidle_idle_call()',
   this ensures that we exit 'cpuidle_idle_call()' if governor->select()
   returns  negative value]
Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

drivers/cpuidle/cpuidle.c

@@ -133,6 +133,9 @@ int cpuidle_idle_call(void)
 
 	/* ask the governor for the next state */
 	next_state = cpuidle_curr_governor->select(drv, dev);
+	if (next_state < 0)
+		return -EBUSY;
+
 	if (need_resched()) {
 		dev->last_residency = 0;
 		/* give the governor an opportunity to reflect on the outcome */

drivers/cpuidle/governors/menu.c

@@ -297,7 +297,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 		data->needs_update = 0;
 	}
 
-	data->last_state_idx = 0;
+	data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1;
 	data->exit_us = 0;
 
 	/* Special case when user has set very strict latency requirement */