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>
diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
index 0ba6ea2..ee39aca 100644
--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -78,3 +78,23 @@
 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.