Bang-bang thermal governor uses trip point hysteresis to make decisions. Hysteresis is a required property in the device tree for trip points, but it is an optional thermal zone device operation. Hence, we need to check whether the function pointer is valid or not.
If it is not available, we assume the hysteresis to be zero. Consequently, a highly varying temperature will make the governor continuosly switch a cooling device ON and OFF. CC: Zhang Rui <[email protected]> CC: Eduardo Valentin <[email protected]> CC: Peter Feuerer <[email protected]> Signed-off-by: Michele Di Giorgio <[email protected]> --- Using trip_hyst == 0 makes the governor work sensibly but may cause oscillations of the control signals of a cooling device. An alternative to this could be to fail the registration of the thermal governor. Another way would be to set the default value of the hysteresis to x% of the trip temperature, to make the governor less sensitive to highly varying inputs. drivers/thermal/gov_bang_bang.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/thermal/gov_bang_bang.c b/drivers/thermal/gov_bang_bang.c index 39d1519..bb118a1 100644 --- a/drivers/thermal/gov_bang_bang.c +++ b/drivers/thermal/gov_bang_bang.c @@ -29,7 +29,13 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip) struct thermal_instance *instance; tz->ops->get_trip_temp(tz, trip, &trip_temp); - tz->ops->get_trip_hyst(tz, trip, &trip_hyst); + + if (!tz->ops->get_trip_hyst) { + pr_warn_once("Undefined get_trip_hyst for thermal zone %s - " + "running with default hysteresis zero\n", tz->type); + trip_hyst = 0; + } else + tz->ops->get_trip_hyst(tz, trip, &trip_hyst); dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n", trip, trip_temp, tz->temperature, -- 1.9.1
