6.5-stable review patch. If anyone has any objections, please let me know.
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From: Nícolas F. R. A. Prado nfraprado@collabora.com
[ Upstream commit cf3986f8c01d355490d0ac6024391b989a9d1e9d ]
When searching for the trip points that need to be set, the nearest higher trip point's temperature is used for the high trip, while the nearest lower trip point's temperature minus the hysteresis is used for the low trip. The issue with this logic is that when the current temperature is inside a trip point's hysteresis range, both high and low trips will come from the same trip point. As a consequence instability can still occur like this: * the temperature rises slightly and enters the hysteresis range of a trip point * polling happens and updates the trip points to the hysteresis range * the temperature falls slightly, exiting the hysteresis range, crossing the trip point and triggering an IRQ, the trip points are updated * repeat
So even though the current hysteresis implementation prevents instability from happening due to IRQs triggering on the same temperature value, both ways, it doesn't prevent it from happening due to an IRQ on one way and polling on the other.
To properly implement a hysteresis behavior, when inside the hysteresis range, don't update the trip points. This way, the previously set trip points will stay in effect, which will in a way remember the previous state (if the temperature signal came from above or below the range) and therefore have the right trip point already set.
The exception is if there was no previous trip point set, in which case a previous state doesn't exist, and so it's sensible to allow the hysteresis range as trip points.
The following logs show the current behavior when running on a real machine:
[ 202.524658] thermal thermal_zone0: new temperature boundaries: -2147483647 < x < 40000 203.562817: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=36986 temp=37979 [ 203.562845] thermal thermal_zone0: new temperature boundaries: 37000 < x < 40000 204.176059: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=37979 temp=40028 [ 204.176089] thermal thermal_zone0: new temperature boundaries: 37000 < x < 100000 205.226813: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=40028 temp=38652 [ 205.226842] thermal thermal_zone0: new temperature boundaries: 37000 < x < 40000
And with this patch applied:
[ 184.933415] thermal thermal_zone0: new temperature boundaries: -2147483647 < x < 40000 185.981182: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=36986 temp=37872 186.744685: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=37872 temp=40058 [ 186.744716] thermal thermal_zone0: new temperature boundaries: 37000 < x < 100000 187.773284: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=40058 temp=38698
Fixes: 060c034a9741 ("thermal: Add support for hardware-tracked trip points") Signed-off-by: Nícolas F. R. A. Prado nfraprado@collabora.com Reviewed-by: AngeloGioacchino Del Regno angelogioacchino.delregno@collabora.com Co-developed-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/thermal/thermal_trip.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/drivers/thermal/thermal_trip.c b/drivers/thermal/thermal_trip.c index 907f3a4d7bc8c..21736e02fa360 100644 --- a/drivers/thermal/thermal_trip.c +++ b/drivers/thermal/thermal_trip.c @@ -57,6 +57,7 @@ void __thermal_zone_set_trips(struct thermal_zone_device *tz) { struct thermal_trip trip; int low = -INT_MAX, high = INT_MAX; + bool same_trip = false; int i, ret;
lockdep_assert_held(&tz->lock); @@ -65,6 +66,7 @@ void __thermal_zone_set_trips(struct thermal_zone_device *tz) return;
for (i = 0; i < tz->num_trips; i++) { + bool low_set = false; int trip_low;
ret = __thermal_zone_get_trip(tz, i , &trip); @@ -73,18 +75,31 @@ void __thermal_zone_set_trips(struct thermal_zone_device *tz)
trip_low = trip.temperature - trip.hysteresis;
- if (trip_low < tz->temperature && trip_low > low) + if (trip_low < tz->temperature && trip_low > low) { low = trip_low; + low_set = true; + same_trip = false; + }
if (trip.temperature > tz->temperature && - trip.temperature < high) + trip.temperature < high) { high = trip.temperature; + same_trip = low_set; + } }
/* No need to change trip points */ if (tz->prev_low_trip == low && tz->prev_high_trip == high) return;
+ /* + * If "high" and "low" are the same, skip the change unless this is the + * first time. + */ + if (same_trip && (tz->prev_low_trip != -INT_MAX || + tz->prev_high_trip != INT_MAX)) + return; + tz->prev_low_trip = low; tz->prev_high_trip = high;