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From:   Lukasz Luba <lukasz.luba@arm.com>
To:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        cw00.choi@samsung.com
Cc:     lukasz.luba@arm.com, myungjoo.ham@samsung.com,
        kyungmin.park@samsung.com
Subject: [PATCH] PM / devfreq: Add sysfs attributes to simple_ondemand governor
Date:   Fri, 15 Jan 2021 17:05:30 +0000
Message-Id: <20210115170530.22603-1-lukasz.luba@arm.com>
Precedence: bulk

The simple_ondemand devfreq governor is used by quite a few devices, like
GPUs, DSPs, memory controllers, etc. It implements algorithm which tries
to predict the device frequency based on past statistics. There are two
tunables for the algorithm: 'upthreshold' and 'downdifferential'. These
tunables change the behavior of the decision, e.g. how fast to increase
the frequency or how rapidly limit the frequency. These values might be
different based on the application which is currently running, e.g.
different behavior is needed for a game than for web browsing or clean
desktop. The patch exports these two tunables so they can be adjusted
based on current need. There is also a check with the allowed ranges
to make sure the values are correct and safe.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
---
 drivers/devfreq/governor_simpleondemand.c | 135 ++++++++++++++++++++++
 1 file changed, 135 insertions(+)

diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
index d57b82a2b570..4b3c182e0a49 100644
--- a/drivers/devfreq/governor_simpleondemand.c
+++ b/drivers/devfreq/governor_simpleondemand.c
@@ -15,6 +15,7 @@
 /* Default constants for DevFreq-Simple-Ondemand (DFSO) */
 #define DFSO_UPTHRESHOLD	(90)
 #define DFSO_DOWNDIFFERENCTIAL	(5)
+#define DFSO_MAX_VALUE		(100)
 static int devfreq_simple_ondemand_func(struct devfreq *df,
 					unsigned long *freq)
 {
@@ -84,15 +85,149 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
 	return 0;
 }
 
+static ssize_t upthreshold_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct devfreq_simple_ondemand_data *data;
+	struct devfreq *df = to_devfreq(dev);
+
+	if (!df->data)
+		return -EINVAL;
+
+	data = df->data;
+
+	return sprintf(buf, "%d\n", data->upthreshold);
+}
+
+static ssize_t upthreshold_store(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *buf, size_t count)
+{
+	struct devfreq_simple_ondemand_data *data;
+	struct devfreq *df = to_devfreq(dev);
+	unsigned int value;
+	int ret;
+
+	if (!df->data)
+		return -EINVAL;
+
+	data = df->data;
+
+	ret = kstrtouint(buf, 10, &value);
+	if (ret < 0)
+		return -EINVAL;
+
+	mutex_lock(&df->lock);
+
+	if (value > DFSO_MAX_VALUE || value <= data->downdifferential) {
+		mutex_unlock(&df->lock);
+		return -EINVAL;
+	}
+
+	data->upthreshold = value;
+	mutex_unlock(&df->lock);
+
+	return count;
+}
+static DEVICE_ATTR_RW(upthreshold);
+
+static ssize_t downdifferential_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct devfreq_simple_ondemand_data *data;
+	struct devfreq *df = to_devfreq(dev);
+
+	if (!df->data)
+		return -EINVAL;
+
+	data = df->data;
+
+	return sprintf(buf, "%d\n", data->downdifferential);
+}
+
+static ssize_t downdifferential_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t count)
+{
+	struct devfreq_simple_ondemand_data *data;
+	struct devfreq *df = to_devfreq(dev);
+	unsigned int value;
+	int ret;
+
+	if (!df->data)
+		return -EINVAL;
+
+	data = df->data;
+
+	ret = kstrtouint(buf, 10, &value);
+	if (ret < 0)
+		return -EINVAL;
+
+	mutex_lock(&df->lock);
+
+	if (value > DFSO_MAX_VALUE || value >= data->upthreshold) {
+		mutex_unlock(&df->lock);
+		return -EINVAL;
+	}
+
+	data->downdifferential = value;
+	mutex_unlock(&df->lock);
+
+	return count;
+}
+static DEVICE_ATTR_RW(downdifferential);
+
+static void devfreq_simple_ondemand_sysfs_setup(struct devfreq *df)
+{
+	struct devfreq_simple_ondemand_data *data;
+	int ret;
+
+	if (!df->data) {
+		/* The memory will be freed automatically */
+		df->data = devm_kzalloc(&df->dev,
+				sizeof(struct devfreq_simple_ondemand_data),
+				GFP_KERNEL);
+		if (!df->data) {
+			dev_warn(&df->dev, "Unable to allocate memory");
+			return;
+		}
+	}
+
+	data = df->data;
+
+	/* After new allocation setup default values, since they are used */
+	if (!data->upthreshold)
+		data->upthreshold = DFSO_UPTHRESHOLD;
+
+	if (!data->downdifferential)
+		data->downdifferential = DFSO_DOWNDIFFERENCTIAL;
+
+	ret = sysfs_create_file(&df->dev.kobj, &dev_attr_upthreshold.attr);
+	if (ret < 0)
+		dev_warn(&df->dev, "Unable to create 'upthreshold' attr\n");
+
+	ret = sysfs_create_file(&df->dev.kobj, &dev_attr_downdifferential.attr);
+	if (ret < 0)
+		dev_warn(&df->dev, "Unable to create 'downdifferential' attr\n");
+}
+
+static void devfreq_simple_ondemand_sysfs_remove(struct devfreq *df)
+{
+	sysfs_remove_file(&df->dev.kobj, &dev_attr_upthreshold.attr);
+	sysfs_remove_file(&df->dev.kobj, &dev_attr_downdifferential.attr);
+}
+
 static int devfreq_simple_ondemand_handler(struct devfreq *devfreq,
 				unsigned int event, void *data)
 {
 	switch (event) {
 	case DEVFREQ_GOV_START:
 		devfreq_monitor_start(devfreq);
+		devfreq_simple_ondemand_sysfs_setup(devfreq);
 		break;
 
 	case DEVFREQ_GOV_STOP:
+		devfreq_simple_ondemand_sysfs_remove(devfreq);
 		devfreq_monitor_stop(devfreq);
 		break;
 
-- 
2.17.1