Hi all, I am trying to modify bang_bang thermal governor The source code I have taken from here https://android.googlesource.com/kernel/common/+/15753588bcd4/drivers/therma... bang bang governor will switch fan on when temperature reaches "trip" temperature and turn the fan off when temperature falls below "trip - hysteresis temperature". These Properties are set in the device file. I am modifying it to operate in three modes, ON, 50% and 100% fan speed depending on the temperature. At 100% fan is noisy, so 50% offers a good compromise for a slightly hotter system but when the system is too hot a 100% fan should be acceptable. Here are the device entries "trips" are set for 70-65 and 65-70 degrees celsius. and cooling maps use fan with state 0, 1 and 2 which are OFF, 50% and 100% thermal-zones { cpu-thermal { trips { cpu_trip_low: active-low { temperature = <65000>; hysteresis = <5000>; type = "active"; }; cpu_trip_high: active-high { temperature = <70000>; hysteresis = <5000>; type = "active"; }; }; cooling-maps { map1 { cooling-device = <&fan 0 1>; trip = <&cpu_trip_low>; }; map2 { cooling-device = <&fan 1 2>; trip = <&cpu_trip_high>; }; }; }; }; The modified algorithm is --- drivers/thermal/gov_bang_bang.c 2024-11-02 05:54:17.385093959 +0000 +++ drivers/thermal/gov_bang_bang.c.orig 2024-11-02 06:09:31.108870820 +0000 @@ -13,6 +13,10 @@ #include "thermal_core.h" +#define FAN_OFF 0 +#define FAN_ON_50 1 +#define FAN_ON_100 2 + static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip) { int trip_temp, trip_hyst; @@ -32,29 +36,59 @@ trip_hyst); list_for_each_entry(instance, &tz->thermal_instances, tz_node) { + + unsigned long upper; + unsigned long lower; + if (instance->trip != trip) continue; + upper = instance->upper; + lower = instance->lower; + + dev_dbg(&instance->cdev->device,"instance state = %ld trip = %d lower = %ld upper= %ld\n", + instance->target, trip,lower, upper); + /* in case fan is in initial state, switch the fan off */ if (instance->target == THERMAL_NO_TARGET) - instance->target = 0; + instance->target = FAN_OFF; - /* in case fan is neither on nor off set the fan to active */ - if (instance->target != 0 && instance->target != 1) { - pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n", - instance->name, instance->target); - instance->target = 1; + /* + * In case fan is not off or running at 50/100% settings, set the fan to + * upper or 50%. + */ + if (instance->target != FAN_OFF && + instance->target != FAN_ON_50 && + instance->target != FAN_ON_100) { + pr_warn("Thermal instance %s controlled by bang-bang has" + " unexpected state: %ld\n lower=%ld upper=%ld", + instance->name, instance->target, + lower, upper); + + if(upper > FAN_ON_100 || lower > FAN_ON_100) + instance->target = FAN_ON_50; + else + instance->target = upper; } /* - * enable fan when temperature exceeds trip_temp and disable - * the fan in case it falls below trip_temp minus hysteresis + * set fan to upper when temperature exceeds trip_temp and set + * fan to lower in case it falls below trip_temp minus hysteresis */ - if (instance->target == 0 && tz->temperature >= trip_temp) - instance->target = 1; - else if (instance->target == 1 && - tz->temperature <= trip_temp - trip_hyst) - instance->target = 0; + if (instance->target < upper && tz->temperature >= trip_temp) { + dev_dbg(&instance->cdev->device, "increase cooling: target" + " = %ld, upper = %ld, temp = %ld\n, trip_temp = %ld\n", + instance->target, upper tz->temperature trip_temp); + instance->target = upper; + + } else if (instance->target > lower && + tz->temperature <= trip_temp - trip_hyst) { + dev_dbg(&instance->cdev->device, "increase cooling: target" + " = %ld, lower = %ld, temp = %ld\n, trip_temp - hyst = %ld\n", + instance->target, lower, tz->temperature, + trip_temp - trip_hyst); + instance->target = lower; + } dev_dbg(&instance->cdev->device, "target=%d\n", (int)instance->target); What I have observed When temperature goes up from 60-65, the fan is switched on at 50%, and when temperature goes on from 65-70, fan is switched on at 100%. When the temperature goes down from 70-65, the fan goes from 100% to 50%, but it doesn't switch off when the temperature goes from 65-60. Fan stays running at 50% when temperature has fallen below the "trip - hysteresis" point. I put some debugs around the code to see what is happening. I observed that "instance->target" is showing two values 0 and 1, which are OFF and 50%, when I expect it to be OFF. My guess is these values are for different trips, since "trip2" has a "lower" set to 1. I am not quite sure how to make sure that value goes back 0 here. Any insight on what I have done wrong and what can I do to make it work? -- Thank you Warm Regards Anuz