cpuidle: menu: Fix menu_select() for CPUIDLE_DRIVER_STATE_START == 0

Commit a9ceb78bc75c (cpuidle,menu: use interactivity_req to disable
polling) exposed a bug in menu_select() causing it to return -1
on systems with CPUIDLE_DRIVER_STATE_START equal to zero, although
it should have returned 0.  As a result, idle states are not entered
by CPUs on those systems.

Namely, on the systems in question data->last_state_idx is initially
equal to -1 and the above commit modified the condition that would
have caused it to be changed to 0 to be less likely to trigger which
exposed the problem.  However, setting data->last_state_idx initially
to -1 doesn't make sense at all and on the affected systems it should
always be set to CPUIDLE_DRIVER_STATE_START (ie. 0) unconditionally,
so make that happen.

Fixes: a9ceb78bc75c (cpuidle,menu: use interactivity_req to disable polling)
Reported-and-tested-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 7b0971d..be0bae0 100644 (file)
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -294,8 +294,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
                data->needs_update = 0;
        }
 
-       data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1;
-
        /* Special case when user has set very strict latency requirement */
        if (unlikely(latency_req == 0))
                return 0;
@@ -326,14 +324,19 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
        if (latency_req > interactivity_req)
                latency_req = interactivity_req;
 
-       /*
-        * We want to default to C1 (hlt), not to busy polling
-        * unless the timer is happening really really soon.
-        */
-       if (interactivity_req > 20 &&
-           !drv->states[CPUIDLE_DRIVER_STATE_START].disabled &&
-               dev->states_usage[CPUIDLE_DRIVER_STATE_START].disable == 0)
+       if (CPUIDLE_DRIVER_STATE_START > 0) {
+               data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1;
+               /*
+                * We want to default to C1 (hlt), not to busy polling
+                * unless the timer is happening really really soon.
+                */
+               if (interactivity_req > 20 &&
+                   !drv->states[CPUIDLE_DRIVER_STATE_START].disabled &&
+                       dev->states_usage[CPUIDLE_DRIVER_STATE_START].disable == 0)
+                       data->last_state_idx = CPUIDLE_DRIVER_STATE_START;
+       } else {
                data->last_state_idx = CPUIDLE_DRIVER_STATE_START;
+       }
 
        /*
         * Find the idle state with the lowest power while satisfying