thermal: core: Use trip lists for trip crossing detection

Modify the thermal core to use three lists of trip points:

 trips_high, containing trips with thresholds strictly above the current
 thermal zone temperature,

 trips_reached, containing trips with thresholds at or below the current
 zone temperature,

 trips_invalid, containing trips with temperature equal to
 THERMAL_ZONE_INVALID,

where the first two lists are always sorted by the current trip
threshold.

For each trip in trips_high, there is no mitigation under way and
the trip threshold is equal to its temperature.  In turn, for each
trip in trips_reached, there is mitigation under way and the trip
threshold is equal to its low temperature.  The trips in trips_invalid,
of course, need not be taken into consideration.

The idea is to make __thermal_zone_device_update() walk trips_high and
trips_reached instead of walking the entire table of trip points in a
thermal zone.  Usually, it will only need to walk a few entries in one
of the lists and check one entry in the other list, depending on the
direction of the zone temperature changes, because crossing many trips
by the zone temperature in one go between two consecutive temperature
checks should be unlikely (if it occurs often, the thermal zone
temperature should probably be checked more often either or there
are too many trips).

This also helps to eliminate one temporary trip list used for trip
crossing notification (only one temporary list is needed for this
purpose instead of two) and the remaining temporary list may be sorted
by the current trip threshold value, like the trips_reached list, so
the additional notify_temp field in struct thermal_trip_desc is not
necessary any more.

Moreover, since the trips_reached and trips_high lists are sorted,
the "low" and "high" values needed by thermal_zone_set_trips() can be
determined in a straightforward way by looking at one end of each list.

Of course, additional work is needed in some places in order to
maintain the ordering of the lists, but it is limited to situations
that should be rare, like updating a trip point temperature or
hysteresis, thermal zone initialization, or system resume.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/2003443.usQuhbGJ8B@rjwysocki.net
[ rjw: Added a comment to thermal_zone_handle_trips() ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/thermal/thermal_core.h b/drivers/thermal/thermal_core.h
index c4759f7222f6..be271e7c8f41 100644
--- a/drivers/thermal/thermal_core.h
+++ b/drivers/thermal/thermal_core.h
@@ -33,7 +33,6 @@ struct thermal_trip_desc {
 	struct thermal_trip_attrs trip_attrs;
 	struct list_head list_node;
 	struct list_head thermal_instances;
-	int notify_temp;
 	int threshold;
 };
 
@@ -78,6 +77,9 @@ struct thermal_governor {
  * @device:	&struct device for this thermal zone
  * @removal:	removal completion
  * @resume:	resume completion
+ * @trips_high:	trips above the current zone temperature
+ * @trips_reached:	trips below or at the current zone temperature
+ * @trips_invalid:	trips with invalid temperature
  * @mode:		current mode of this thermal zone
  * @devdata:	private pointer for device private data
  * @num_trips:	number of trip points the thermal zone supports
@@ -118,6 +120,9 @@ struct thermal_zone_device {
 	struct completion removal;
 	struct completion resume;
 	struct attribute_group trips_attribute_group;
+	struct list_head trips_high;
+	struct list_head trips_reached;
+	struct list_head trips_invalid;
 	enum thermal_device_mode mode;
 	void *devdata;
 	int num_trips;