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>

diff --git a/drivers/thermal/gov_step_wise.c b/drivers/thermal/gov_step_wise.c
index 2ae7198..abe34cf 100644 (file)
--- a/drivers/thermal/gov_step_wise.c
+++ b/drivers/thermal/gov_step_wise.c
@@ -24,7 +24,7 @@
  *       for this trip point
  *    d. if the trend is THERMAL_TREND_DROP_FULL, use lower limit
  *       for this trip point
- * If the temperature is lower than a trip point,
+ * If the temperature is lower than a hysteresis temperature,
  *    a. if the trend is THERMAL_TREND_RAISING, do nothing
  *    b. if the trend is THERMAL_TREND_DROPPING, use lower cooling
  *       state for this trip point, if the cooling state already
@@ -115,7 +115,7 @@ static void update_passive_instance(struct thermal_zone_device *tz,
 
 static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
 {
-       int trip_temp;
+       int trip_temp, hyst_temp;
        enum thermal_trip_type trip_type;
        enum thermal_trend trend;
        struct thermal_instance *instance;
@@ -123,22 +123,23 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
        int old_target;
 
        if (trip == THERMAL_TRIPS_NONE) {
-               trip_temp = tz->forced_passive;
+               hyst_temp = trip_temp = tz->forced_passive;
                trip_type = THERMAL_TRIPS_NONE;
        } else {
                tz->ops->get_trip_temp(tz, trip, &trip_temp);
+               hyst_temp = trip_temp;
+               if (tz->ops->get_trip_hyst) {
+                       tz->ops->get_trip_hyst(tz, trip, &hyst_temp);
+                       hyst_temp = trip_temp - hyst_temp;
+               }
                tz->ops->get_trip_type(tz, trip, &trip_type);
        }
 
        trend = get_tz_trend(tz, trip);
 
-       if (tz->temperature >= trip_temp) {
-               throttle = true;
-               trace_thermal_zone_trip(tz, trip, trip_type);
-       }
-
-       dev_dbg(&tz->device, "Trip%d[type=%d,temp=%d]:trend=%d,throttle=%d\n",
-                               trip, trip_type, trip_temp, trend, throttle);
+       dev_dbg(&tz->device,
+               "Trip%d[type=%d,temp=%d,hyst=%d]:trend=%d,throttle=%d\n",
+               trip, trip_type, trip_temp, hyst_temp, trend, throttle);
 
        mutex_lock(&tz->lock);
 
@@ -147,6 +148,18 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
                        continue;
 
                old_target = instance->target;
+               throttle = false;
+               /*
+                * Lower the mitigation only if the temperature
+                * goes below the hysteresis temperature.
+                */
+               if (tz->temperature >= trip_temp ||
+                  (tz->temperature >= hyst_temp &&
+                  old_target != THERMAL_NO_TARGET)) {
+                       throttle = true;
+                       trace_thermal_zone_trip(tz, trip, 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);