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>

1 files changed, 6 insertions, 3 deletions

diff --git a/include/linux/thermal.h b/include/linux/thermal.h
index 00dacd4dfdce..bac0f52c7a1e 100644
--- a/include/linux/thermal.h
+++ b/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;