drm/panfrost: Add governor data with pre-defined thresholds

The simple_ondemand devfreq governor uses two thresholds to decide about
the frequency change: upthreshold, downdifferential. These two tunable
change the behavior of the governor decision, e.g. how fast to increase
the frequency or how rapidly limit the frequency. This patch adds needed
governor data with thresholds values gathered experimentally in different
workloads.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210121170445.19761-1-lukasz.luba@arm.com

drivers/gpu/drm/panfrost/panfrost_devfreq.c

@@ -130,8 +130,16 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
 	panfrost_devfreq_profile.initial_freq = cur_freq;
 	dev_pm_opp_put(opp);
 
+	/*
+	 * Setup default thresholds for the simple_ondemand governor.
+	 * The values are chosen based on experiments.
+	 */
+	pfdevfreq->gov_data.upthreshold = 45;
+	pfdevfreq->gov_data.downdifferential = 5;
+
 	devfreq = devm_devfreq_add_device(dev, &panfrost_devfreq_profile,
-					  DEVFREQ_GOV_SIMPLE_ONDEMAND, NULL);
+					  DEVFREQ_GOV_SIMPLE_ONDEMAND,
+					  &pfdevfreq->gov_data);
 	if (IS_ERR(devfreq)) {
 		DRM_DEV_ERROR(dev, "Couldn't initialize GPU devfreq\n");
 		ret = PTR_ERR(devfreq);

drivers/gpu/drm/panfrost/panfrost_devfreq.h

@@ -4,6 +4,7 @@
 #ifndef __PANFROST_DEVFREQ_H__
 #define __PANFROST_DEVFREQ_H__
 
+#include <linux/devfreq.h>
 #include <linux/spinlock.h>
 #include <linux/ktime.h>
 
@@ -17,6 +18,7 @@ struct panfrost_devfreq {
 	struct devfreq *devfreq;
 	struct opp_table *regulators_opp_table;
 	struct thermal_cooling_device *cooling;
+	struct devfreq_simple_ondemand_data gov_data;
 	bool opp_of_table_added;
 
 	ktime_t busy_time;