cpuidle: fix fallback mechanism for suspend to idle in absence of enter_freeze

Commit 51164251 "sched / idle: Drop default_idle_call() fallback
from call_cpuidle()" made find_deepest_state() return non-negative
value and check all the states with index > 0.  Also as a result,
find_deepest_state() returns 0 even when enter_freeze callbacks are not
implemented and enter_freeze_proper() is called which ends up crashing
the kernel.

This patch updates the check for index > 0 in cpuidle_enter_freeze and
cpuidle_idle_call(when idle_should_freeze is true) to restore the
suspend-to-idle functionality in absence of enter_freeze callback.

Fixes: 51164251 "sched / idle: Drop default_idle_call() fallback from call_cpuidle()"
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpuidle/cpuidle.c

@@ -153,7 +153,7 @@ int cpuidle_enter_freeze(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	 * be frozen safely.
 	 */
 	index = find_deepest_state(drv, dev, UINT_MAX, 0, true);
-	if (index >= 0)
+	if (index > 0)
 		enter_freeze_proper(drv, dev, index);
 
 	return index;

kernel/sched/idle.c

@@ -162,7 +162,7 @@ static void cpuidle_idle_call(void)
 	 */
 	if (idle_should_freeze()) {
 		entered_state = cpuidle_enter_freeze(drv, dev);
-		if (entered_state >= 0) {
+		if (entered_state > 0) {
 			local_irq_enable();
 			goto exit_idle;
 		}