3 files changed, 31 insertions, 4 deletions

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 8e5938c9c7d6..ade279d29f1e 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -940,6 +940,9 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
         if (df->governor == governor) {
                 ret = 0;
                 goto out;
+        } else if (df->governor->immutable || governor->immutable) {
+                ret = -EINVAL;
+                goto out;
         }
 
         if (df->governor) {
@@ -969,13 +972,33 @@ static ssize_t available_governors_show(struct device *d,
                                         struct device_attribute *attr,
                                         char *buf)
 {
-        struct devfreq_governor *tmp_governor;
+        struct devfreq *df = to_devfreq(d);
         ssize_t count = 0;
 
         mutex_lock(&devfreq_list_lock);
-        list_for_each_entry(tmp_governor, &devfreq_governor_list, node)
-                count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
-                                   "%s ", tmp_governor->name);
+
+        /*
+         * The devfreq with immutable governor (e.g., passive) shows
+         * only own governor.
+         */
+        if (df->governor->immutable) {
+                count = scnprintf(&buf[count], DEVFREQ_NAME_LEN,
+                                   "%s ", df->governor_name);
+        /*
+         * The devfreq device shows the registered governor except for
+         * immutable governors such as passive governor .
+         */
+        } else {
+                struct devfreq_governor *governor;
+
+                list_for_each_entry(governor, &devfreq_governor_list, node) {
+                        if (governor->immutable)
+                                continue;
+                        count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
+                                           "%s ", governor->name);
+                }
+        }
+
         mutex_unlock(&devfreq_list_lock);
 
         /* Truncate the trailing space */
diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
index 9ef46e2592c4..93795b32dc09 100644
--- a/drivers/devfreq/governor_passive.c
+++ b/drivers/devfreq/governor_passive.c
@@ -179,6 +179,7 @@ static int devfreq_passive_event_handler(struct devfreq *devfreq,
 
 static struct devfreq_governor devfreq_passive = {
         .name = "passive",
+        .immutable = 1,
         .get_target_freq = devfreq_passive_get_target_freq,
         .event_handler = devfreq_passive_event_handler,
 };
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index 2de4e2eea180..e0acb0e5243b 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -104,6 +104,8 @@ struct devfreq_dev_profile {
  * struct devfreq_governor - Devfreq policy governor
  * @node:               list node - contains registered devfreq governors
  * @name:               Governor's name
+ * @immutable:          Immutable flag for governor. If the value is 1,
+ *                      this govenror is never changeable to other governor.
  * @get_target_freq:    Returns desired operating frequency for the device.
  *                      Basically, get_target_freq will run
  *                      devfreq_dev_profile.get_dev_status() to get the
@@ -121,6 +123,7 @@ struct devfreq_governor {
         struct list_head node;
 
         const char name[DEVFREQ_NAME_LEN];
+        const unsigned int immutable;
         int (*get_target_freq)(struct devfreq *this, unsigned long *freq);
         int (*event_handler)(struct devfreq *devfreq,
                                 unsigned int event, void *data);