drivers: thermal: step_wise: add support for hysteresis

Step wise governor increases the mitigation level when the temperature
goes above a threshold and will decrease the mitigation when the
temperature falls below the threshold. If it were a case, where the
temperature hovers around a threshold, the mitigation will be applied
and removed at every iteration. This reaction to the temperature is
inefficient for performance.

The use of hysteresis temperature could avoid this ping-pong of
mitigation by relaxing the mitigation to happen only when the
temperature goes below this lower hysteresis value.

Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>
Signed-off-by: Lina Iyer <ilina@codeaurora.org>
drivers: thermal: step_wise: avoid throttling at hysteresis temperature after dropping below it

Signed-off-by: Serge Schneider <serge@raspberrypi.com>

diff --git a/drivers/thermal/gov_step_wise.c b/drivers/thermal/gov_step_wise.c
index 849dc1e..394c6de 100644 (file)
--- a/drivers/thermal/gov_step_wise.c
+++ b/drivers/thermal/gov_step_wise.c
@@ -86,22 +86,33 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip_id
        struct thermal_instance *instance;
        bool throttle = false;
        int old_target;
+       int hyst_temp;
 
        trend = get_tz_trend(tz, trip_id);
 
-       if (tz->temperature >= trip->temperature) {
-               throttle = true;
-               trace_thermal_zone_trip(tz, trip_id, trip->type);
-       }
+       hyst_temp = trip->temperature - trip->hysteresis;
 
-       dev_dbg(&tz->device, "Trip%d[type=%d,temp=%d]:trend=%d,throttle=%d\n",
-               trip_id, trip->type, trip->temperature, trend, throttle);
+       dev_dbg(&tz->device,
+               "Trip%d[type=%d,temp=%d,hyst=%d]:trend=%d,throttle=%d\n",
+               trip_id, trip->type, trip->temperature, hyst_temp, trend, throttle);
 
        list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
                if (instance->trip != trip)
                        continue;
 
                old_target = instance->target;
+               throttle = false;
+               /*
+                * Lower the mitigation only if the temperature
+                * goes below the hysteresis temperature.
+                */
+               if (tz->temperature >= trip->temperature ||
+                  (tz->temperature >= hyst_temp &&
+                   old_target == instance->upper)) {
+                       throttle = true;
+                       trace_thermal_zone_trip(tz, trip_id, trip->type);
+               }
+
                instance->target = get_target_state(instance, trend, throttle);
                dev_dbg(&instance->cdev->device, "old_target=%d, target=%d\n",
                                        old_target, (int)instance->target);