6.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Daniel Lezcano daniel.lezcano@linaro.org
commit f67cf45deedb118af302534643627ce59074e8eb upstream.
It has been reported the commit cf3986f8c01d3 introduced a regression when the temperature is wavering in the hysteresis region. The mitigation stops leading to an uncontrolled temperature increase until reaching the critical trip point.
Here what happens:
* 'throttle' is when the current temperature is greater than the trip point temperature * 'target' is the mitigation level * 'passive' is positive when there is a mitigation, zero otherwise * these values are computed in the step_wise governor
Configuration:
trip point 1: temp=95°C, hyst=5°C (passive) trip point 2: temp=115°C, hyst=0°C (critical) governor: step_wise
1. The temperature crosses the way up the trip point 1 at 95°C
- trend=raising - throttle=1, target=1 - passive=1 - set_trips: low=90°C, high=115°C
2. The temperature decreases but stays in the hysteresis region at 93°C
- trend=dropping - throttle=0, target=0 - passive=1
Before cf3986f8c01d3 - set_trips: low=90°C, high=95°C
After cf3986f8c01d3 - set_trips: low=90°C, high=115°C
3. The temperature increases a bit but stays in the hysteresis region at 94°C (so below the trip point 1 temp 95°C)
- trend=raising - throttle=0, target=0 - passive=1
Before cf3986f8c01d3 - set_trips: low=90°C, high=95°C
After cf3986f8c01d3 - set_trips: low=90°C, high=115°C
4. The temperature decreases but stays in the hysteresis region at 93°C
- trend=dropping - throttle=0, target=THERMAL_NO_TARGET - passive=0
Before cf3986f8c01d3 - set_trips: low=90°C, high=95°C
After cf3986f8c01d3 - set_trips: low=90°C, high=115°C
At this point, the 'passive' value is zero, there is no mitigation, the temperature is in the hysteresis region, the next trip point is 115°C. As 'passive' is zero, the timer to monitor the thermal zone is disabled. Consequently if the temperature continues to increase, no mitigation will happen and it will reach the 115°C trip point and reboot.
Before the optimization, the high boundary would have been 95°C, thus triggering the mitigation again and rearming the polling timer.
The optimization make sense but given the current implementation of the step_wise governor collaborating via this 'passive' flag with the core framework it can not work.
From a higher perspective it seems like there is a problem between the
governor which sets a variable to be used by the core framework. That sounds akward and it would make much more sense if the core framework controls the governor and not the opposite. But as the devil hides in the details, there are some subtilities to be addressed before.
Elaborating those would be out of the scope this changelog. So let's stay simple and revert the change first to fixup all broken mobile platforms.
This reverts commit cf3986f8c01d3 ("thermal: core: Don't update trip points inside the hysteresis range") and takes a conflict with commit 0c0c4740c9d26 ("0c0c4740c9d2 thermal: trip: Use for_each_trip() in __thermal_zone_set_trips()") in drivers/thermal/thermal_trip.c into account.
Fixes: cf3986f8c01d3 ("thermal: core: Don't update trip points inside the hysteresis range") Reported-by: Manaf Meethalavalappu Pallikunhi quic_manafm@quicinc.com Signed-off-by: Daniel Lezcano daniel.lezcano@linaro.org Acked-by: Nícolas F. R. A. Prado nfraprado@collabora.com Cc: 6.7+ stable@vger.kernel.org # 6.7+ Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/thermal/thermal_trip.c | 19 ++----------------- 1 file changed, 2 insertions(+), 17 deletions(-)
--- a/drivers/thermal/thermal_trip.c +++ b/drivers/thermal/thermal_trip.c @@ -65,7 +65,6 @@ void __thermal_zone_set_trips(struct the { const struct thermal_trip *trip; int low = -INT_MAX, high = INT_MAX; - bool same_trip = false; int ret;
lockdep_assert_held(&tz->lock); @@ -74,36 +73,22 @@ void __thermal_zone_set_trips(struct the return;
for_each_trip(tz, trip) { - bool low_set = false; int trip_low;
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;