thermal: fair_share: generalize the weight concept

The fair share governor has the concept of weights, which is the
influence of each cooling device in a thermal zone.  The current
implementation forces the weights of all cooling devices in a thermal
zone to add up to a 100.  This complicates setups, as you need to know
in advance how many cooling devices you are going to have.  If you bind a
new cooling device, you have to modify all the other cooling devices
weights, which is error prone.  Furthermore, you can't specify a
"default" weight for platforms since that default value depends on the
number of cooling devices in the platform.

This patch generalizes the concept of weight by allowing any number to
be a "weight".  Weights are now relative to each other.  Platforms that
don't specify weights get the same default value for all their cooling
devices, so all their cdevs are considered to be equally influential.

It's important to note that previous users of the weights don't need to
alter the code: percentages continue to work as they used to.  This
patch just removes the constraint of all the weights in a thermal zone
having to add up to a 100.  If they do, you get the same behavior as
before.  If they don't, fair share now works for that platform.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Durgadoss R <durgadoss.r@intel.com>
Acked-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

Documentation/thermal/sysfs-api.txt

@@ -129,9 +129,15 @@ temperature) and throttle appropriate devices.
     This structure defines the following parameters that are used to bind
     a zone with a cooling device for a particular trip point.
     .cdev: The cooling device pointer
-    .weight: The 'influence' of a particular cooling device on this zone.
-             This is on a percentage scale. The sum of all these weights
-             (for a particular zone) cannot exceed 100.
+    .weight: The 'influence' of a particular cooling device on this
+             zone. This is relative to the rest of the cooling
+             devices. For example, if all cooling devices have a
+             weight of 1, then they all contribute the same. You can
+             use percentages if you want, but it's not mandatory. A
+             weight of 0 means that this cooling device doesn't
+             contribute to the cooling of this zone unless all cooling
+             devices have a weight of 0. If all weights are 0, then
+             they all contribute the same.
     .trip_mask:This is a bit mask that gives the binding relation between
                this thermal zone and cdev, for a particular trip point.
                If nth bit is set, then the cdev and thermal zone are bound

drivers/thermal/fair_share.c

@@ -59,13 +59,13 @@ static int get_trip_level(struct thermal_zone_device *tz)
 }
 
 static long get_target_state(struct thermal_zone_device *tz,
-		struct thermal_cooling_device *cdev, int weight, int level)
+		struct thermal_cooling_device *cdev, int percentage, int level)
 {
 	unsigned long max_state;
 
 	cdev->ops->get_max_state(cdev, &max_state);
 
-	return (long)(weight * level * max_state) / (100 * tz->trips);
+	return (long)(percentage * level * max_state) / (100 * tz->trips);
 }
 
 /**
@@ -77,7 +77,7 @@ static long get_target_state(struct thermal_zone_device *tz,
  *
  * Parameters used for Throttling:
  * P1. max_state: Maximum throttle state exposed by the cooling device.
- * P2. weight[i]/100:
+ * P2. percentage[i]/100:
  *	How 'effective' the 'i'th device is, in cooling the given zone.
  * P3. cur_trip_level/max_no_of_trips:
  *	This describes the extent to which the devices should be throttled.
@@ -89,16 +89,32 @@ static long get_target_state(struct thermal_zone_device *tz,
 static int fair_share_throttle(struct thermal_zone_device *tz, int trip)
 {
 	struct thermal_instance *instance;
+	int total_weight = 0;
+	int total_instance = 0;
 	int cur_trip_level = get_trip_level(tz);
 
 	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
+		if (instance->trip != trip)
+			continue;
+
+		total_weight += instance->weight;
+		total_instance++;
+	}
+
+	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
+		int percentage;
 		struct thermal_cooling_device *cdev = instance->cdev;
 
 		if (instance->trip != trip)
 			continue;
 
-		instance->target = get_target_state(tz, cdev,
-					instance->weight, cur_trip_level);
+		if (!total_weight)
+			percentage = 100 / total_instance;
+		else
+			percentage = (instance->weight * 100) / total_weight;
+
+		instance->target = get_target_state(tz, cdev, percentage,
+						    cur_trip_level);
 
 		instance->cdev->updated = false;
 		thermal_cdev_update(cdev);

include/linux/thermal.h

@@ -217,9 +217,12 @@ struct thermal_bind_params {
 
 	/*
 	 * This is a measure of 'how effectively these devices can
-	 * cool 'this' thermal zone. The shall be determined by platform
-	 * characterization. This is on a 'percentage' scale.
-	 * See Documentation/thermal/sysfs-api.txt for more information.
+	 * cool 'this' thermal zone. It shall be determined by
+	 * platform characterization. This value is relative to the
+	 * rest of the weights so a cooling device whose weight is
+	 * double that of another cooling device is twice as
+	 * effective. See Documentation/thermal/sysfs-api.txt for more
+	 * information.
 	 */
 	int weight;