sched / idle: Drop default_idle_call() fallback from call_cpuidle()

After commit 9c4b2867ed (cpuidle: menu: Fix menu_select() for
CPUIDLE_DRIVER_STATE_START == 0) it is clear that menu_select()
cannot return negative values.  Moreover, ladder_select_state()
will never return a negative value too, so make find_deepest_state()
return non-negative values too and drop the default_idle_call()
fallback from call_cpuidle().

This eliminates one branch from the idle loop and makes the governors
and find_deepest_state() handle the case when all states have been
disabled from sysfs consistently.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/cpuidle/cpuidle.c

@@ -79,9 +79,9 @@ static int find_deepest_state(struct cpuidle_driver *drv,
 			      bool freeze)
 {
 	unsigned int latency_req = 0;
-	int i, ret = -ENXIO;
+	int i, ret = 0;
 
-	for (i = 0; i < drv->state_count; i++) {
+	for (i = 1; i < drv->state_count; i++) {
 		struct cpuidle_state *s = &drv->states[i];
 		struct cpuidle_state_usage *su = &dev->states_usage[i];
 
@@ -243,7 +243,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
  * @drv: the cpuidle driver
  * @dev: the cpuidle device
  *
- * Returns the index of the idle state.
+ * Returns the index of the idle state.  The return value must not be negative.
  */
 int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {

kernel/sched/idle.c

@@ -97,12 +97,6 @@ void default_idle_call(void)
 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 		      int next_state)
 {
-	/* Fall back to the default arch idle method on errors. */
-	if (next_state < 0) {
-		default_idle_call();
-		return next_state;
-	}
-
 	/*
 	 * The idle task must be scheduled, it is pointless to go to idle, just
 	 * update no idle residency and return.