PM / devfreq: allow sysfs governor node to switch governor

This allows us to select governor runtime from the
default configuration without having to rebuild kernel
or the devfreq driver using the sysfs node:
/sys/class/devfreq/.../governor
cat of the governor will return valid governor
and an echo 'governor_name'>governor will switch
governor

Cc: Rajagopal Venkat <[email protected]>
Cc: MyungJoo Ham <[email protected]>
Cc: Kyungmin Park <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Kevin Hilman <[email protected]>
Cc: [email protected]
Cc: [email protected]

Signed-off-by: Nishanth Menon <[email protected]>
Acked-by: MyungJoo Ham <[email protected]>
Signed-off-by: MyungJoo Ham <[email protected]>

2 files changed, 45 insertions, 2 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
index 40f98a9428dc..66876debca18 100644
--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -11,7 +11,7 @@ What:		/sys/class/devfreq/.../governor
 Date:		September 2011
 Contact:	MyungJoo Ham <[email protected]>
 Description:
-		The /sys/class/devfreq/.../governor shows the name of the
+		The /sys/class/devfreq/.../governor show or set the name of the
 		governor used by the corresponding devfreq object.
 
 What:		/sys/class/devfreq/.../cur_freq
diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 0d7be03d561f..ff960f084c11 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -688,6 +688,49 @@ static ssize_t show_governor(struct device *dev,
 	return sprintf(buf, "%s\n", to_devfreq(dev)->governor->name);
 }
 
+static ssize_t store_governor(struct device *dev, struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct devfreq *df = to_devfreq(dev);
+	int ret;
+	char str_governor[DEVFREQ_NAME_LEN + 1];
+	struct devfreq_governor *governor;
+
+	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
+	if (ret != 1)
+		return -EINVAL;
+
+	mutex_lock(&devfreq_list_lock);
+	governor = find_devfreq_governor(str_governor);
+	if (IS_ERR(governor)) {
+		ret = PTR_ERR(governor);
+		goto out;
+	}
+	if (df->governor == governor)
+		goto out;
+
+	if (df->governor) {
+		ret = df->governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
+		if (ret) {
+			dev_warn(dev, "%s: Governor %s not stopped(%d)\n",
+				 __func__, df->governor->name, ret);
+			goto out;
+		}
+	}
+	df->governor = governor;
+	strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN);
+	ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
+	if (ret)
+		dev_warn(dev, "%s: Governor %s not started(%d)\n",
+			 __func__, df->governor->name, ret);
+out:
+	mutex_unlock(&devfreq_list_lock);
+
+	if (!ret)
+		ret = count;
+	return ret;
+}
+
 static ssize_t show_freq(struct device *dev,
 			 struct device_attribute *attr, char *buf)
 {
@@ -873,7 +916,7 @@ static ssize_t show_trans_table(struct device *dev, struct device_attribute *att
 }
 
 static struct device_attribute devfreq_attrs[] = {
-	__ATTR(governor, S_IRUGO, show_governor, NULL),
+	__ATTR(governor, S_IRUGO | S_IWUSR, show_governor, store_governor),
 	__ATTR(cur_freq, S_IRUGO, show_freq, NULL),
 	__ATTR(available_frequencies, S_IRUGO, show_available_freqs, NULL),
 	__ATTR(target_freq, S_IRUGO, show_target_freq, NULL),