PM / devfreq: add comments and Documentation

- Added missing ABI documents
- Added comments to clarify the objectives of functions

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Rajagopal Venkat <rajagopal.venkat@linaro.org>

Documentation/ABI/testing/sysfs-class-devfreq

@@ -78,3 +78,23 @@ Contact:	Nishanth Menon <nm@ti.com>
 Description:
 		The /sys/class/devfreq/.../available_governors shows
 		currently available governors in the system.
+
+What:		/sys/class/devfreq/.../min_freq
+Date:		January 2013
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		The /sys/class/devfreq/.../min_freq shows and stores
+		the minimum frequency requested by users. It is 0 if
+		the user does not care. min_freq overrides the
+		frequency requested by governors.
+
+What:		/sys/class/devfreq/.../max_freq
+Date:		January 2013
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		The /sys/class/devfreq/.../max_freq shows and stores
+		the maximum frequency requested by users. It is 0 if
+		the user does not care. max_freq overrides the
+		frequency requested by governors and min_freq.
+		The max_freq overrides min_freq because max_freq may be
+		used to throttle devices to avoid overheating.

drivers/devfreq/devfreq.c

@@ -527,6 +527,8 @@ EXPORT_SYMBOL(devfreq_add_device);
 /**
  * devfreq_remove_device() - Remove devfreq feature from a device.
  * @devfreq:	the devfreq instance to be removed
+ *
+ * The opposite of devfreq_add_device().
  */
 int devfreq_remove_device(struct devfreq *devfreq)
 {
@@ -542,6 +544,10 @@ EXPORT_SYMBOL(devfreq_remove_device);
 /**
  * devfreq_suspend_device() - Suspend devfreq of a device.
  * @devfreq: the devfreq instance to be suspended
+ *
+ * This function is intended to be called by the pm callbacks
+ * (e.g., runtime_suspend, suspend) of the device driver that
+ * holds the devfreq.
  */
 int devfreq_suspend_device(struct devfreq *devfreq)
 {
@@ -559,6 +565,10 @@ EXPORT_SYMBOL(devfreq_suspend_device);
 /**
  * devfreq_resume_device() - Resume devfreq of a device.
  * @devfreq: the devfreq instance to be resumed
+ *
+ * This function is intended to be called by the pm callbacks
+ * (e.g., runtime_resume, resume) of the device driver that
+ * holds the devfreq.
  */
 int devfreq_resume_device(struct devfreq *devfreq)
 {

include/linux/devfreq.h

@@ -181,6 +181,8 @@ extern struct devfreq *devfreq_add_device(struct device *dev,
 				  const char *governor_name,
 				  void *data);
 extern int devfreq_remove_device(struct devfreq *devfreq);
+
+/* Supposed to be called by PM_SLEEP/PM_RUNTIME callbacks */
 extern int devfreq_suspend_device(struct devfreq *devfreq);
 extern int devfreq_resume_device(struct devfreq *devfreq);