Messages in this thread | | | Date | Tue, 12 Jul 2022 12:29:12 +0100 | Subject | Re: [PATCH v2 3/3] thermal/core: Fix thermal trip cross point | From | Lukasz Luba <> |
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On 7/8/22 19:32, Daniel Lezcano wrote: > The routine doing trip point crossing the way up or down is actually > wrong. > > A trip point is composed with a trip temperature and a hysteresis. > > The trip temperature is used to detect when the trip point is crossed > the way up. > > The trip temperature minus the hysteresis is used to detect when the > trip point is crossed the way down. > > |-----------low--------high------------| > |<--------->| > | hyst | > | | > | -|--> crossed the way up > | > <---|-- crossed the way down > > For that, there is a two point comparison: the current temperature and > the previous temperature. > > The actual code assumes if the current temperature is greater than the > trip temperature and the previous temperature was lesser, then the > trip point is crossed the way up. That is true only if we crossed the > way down the low temperature boundary from the previous temperature or > if the hysteresis is zero. The temperature can decrease between the > low and high, so the trip point is not crossed the way down and then > increase again and cross the high temperature raising a new trip point > crossed detection which is incorrect. The same scenario happens when > crossing the way down. > > The trip point crossing the way up and down must act as parenthesis, a > trip point down must close a trip point up. Today we have multiple > trip point up without the corresponding trip point down. > > In order to fix that, we store the previous trip point which gives the > information about the previous trip and we change the trip point > browsing order depending on the temperature trend: in the ascending > order when the temperature trend is raising, otherwise in the > descending order. > > As a sidenote, the thermal_zone_device structure has already the > prev_trip_low and prev_trip_high information which are used by the > thermal_zone_set_trips() function. This one can be changed to be > triggered by the trip temperature crossing function, which makes more > sense, and the two fields will disappear. > > Tested on a rk3399-rock960 with thermal stress and 4 trip points. Also > tested with temperature emulation to create a temperature jump > directly to the second trip point. > > Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> > --- > V2: > - As spotted by Zhang Rui, the trip cross notification does not > work if the temperature drops and crosses two trip points in the > same update interval. In order to fix that, we browse the trip point > in the ascending order when the temperature trend is raising, > otherwise in the descending order. > --- > drivers/thermal/thermal_core.c | 46 +++++++++++++++++++++++++--------- > include/linux/thermal.h | 2 ++ > 2 files changed, 36 insertions(+), 12 deletions(-) > > diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c > index f66036b3daae..89926e029378 100644 > --- a/drivers/thermal/thermal_core.c > +++ b/drivers/thermal/thermal_core.c > @@ -357,19 +357,35 @@ static void handle_critical_trips(struct thermal_zone_device *tz, > static void handle_thermal_trip_crossed(struct thermal_zone_device *tz, int trip, > int trip_temp, int trip_hyst, enum thermal_trip_type trip_type) > { > + int trip_low_temp = trip_temp - trip_hyst; > + > if (tz->last_temperature == THERMAL_TEMP_INVALID) > return; > > - if (tz->last_temperature < trip_temp && > - tz->temperature >= trip_temp) { > - thermal_notify_tz_trip_up(tz->id, trip, > - tz->temperature); > - } > - > - if (tz->last_temperature >= trip_temp && > - tz->temperature < (trip_temp - trip_hyst)) { > - thermal_notify_tz_trip_down(tz->id, trip, > - tz->temperature); > + /* > + * Due to the hysteresis, a third information is needed to > + * detect when the temperature is wavering between the > + * trip_low_temp and the trip_temp. A trip point is crossed > + * the way up only if the temperature is above it while the > + * previous temperature was below *and* we crossed the > + * trip_temp_low before. The previous trip point give us the > + * previous trip point transition. The similar problem exists > + * when crossing the way down. > + * > + * Note the mechanism works only if the caller of the function > + * invoke the function with the trip point ascending or > + * descending regarding the temperature trend. A temperature > + * drop trend will browse the trip point in the descending > + * order > + */ > + if (tz->last_temperature < trip_temp && tz->temperature >= trip_temp && > + trip != tz->prev_trip) { > + thermal_notify_tz_trip_up(tz->id, trip, tz->temperature); > + tz->prev_trip = trip; > + } else if (tz->last_temperature >= trip_low_temp && tz->temperature < trip_low_temp && > + trip == tz->prev_trip) { > + thermal_notify_tz_trip_down(tz->id, trip, tz->temperature); > + tz->prev_trip = trip - 1; > } > } > > @@ -427,6 +443,7 @@ static void thermal_zone_device_init(struct thermal_zone_device *tz) > { > struct thermal_instance *pos; > tz->temperature = THERMAL_TEMP_INVALID; > + tz->prev_trip = -1; > tz->prev_low_trip = -INT_MAX; > tz->prev_high_trip = INT_MAX; > list_for_each_entry(pos, &tz->thermal_instances, tz_node) > @@ -511,8 +528,13 @@ void thermal_zone_device_update(struct thermal_zone_device *tz, > > tz->notify_event = event; > > - for (count = 0; count < tz->trips; count++) > - handle_thermal_trip(tz, count); > + if (tz->last_temperature <= tz->temperature) { > + for (count = 0; count < tz->trips; count++) > + handle_thermal_trip(tz, count); > + } else { > + for (count = tz->prev_trip; count >= 0; count--) > + handle_thermal_trip(tz, count); > + }
In general the code look good. I have one question, though: Is it always true that these trip points coming from the DT and parsed in thermal_of_build_thermal_zone() populated by for_each_child_of_node(child, gchild) { thermal_of_populate_trip(gchild, &tz->trips[i++]);
are always defined in right order in DT?
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