PM / devfreq: Add common sysfs interfaces

Device specific sysfs interface /sys/devices/.../power/devfreq_*
- governor	R: name of governor
- cur_freq	R: current frequency
- polling_interval	R: polling interval in ms given with devfreq profile
			W: update polling interval.
- central_polling	R: 1 if polling is managed by devfreq framework

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Mike Turquette <mturquette@ti.com>
Acked-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
--
 Documentation/ABI/testing/sysfs-class-devfreq |   44 ++++++++++++++++
 drivers/devfreq/devfreq.c                     |   69 ++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-class-devfreq

Documentation/ABI/testing/sysfs-class-devfreq

@@ -0,0 +1,44 @@
+What:		/sys/class/devfreq/.../
+Date:		September 2011
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		Provide a place in sysfs for the devfreq objects.
+		This allows accessing various devfreq specific variables.
+		The name of devfreq object denoted as ... is same as the
+		name of device using devfreq.
+
+What:		/sys/class/devfreq/.../governor
+Date:		September 2011
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		The /sys/class/devfreq/.../governor shows the name of the
+		governor used by the corresponding devfreq object.
+
+What:		/sys/class/devfreq/.../cur_freq
+Date:		September 2011
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		The /sys/class/devfreq/.../cur_freq shows the current
+		frequency of the corresponding devfreq object.
+
+What:		/sys/class/devfreq/.../central_polling
+Date:		September 2011
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		The /sys/class/devfreq/.../central_polling shows whether
+		the devfreq ojbect is using devfreq-provided central
+		polling mechanism or not.
+
+What:		/sys/class/devfreq/.../polling_interval
+Date:		September 2011
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		The /sys/class/devfreq/.../polling_interval shows and sets
+		the requested polling interval of the corresponding devfreq
+		object. The values are represented in ms. If the value is
+		less than 1 jiffy, it is considered to be 0, which means
+		no polling. This value is meaningless if the governor is
+		not polling; thus. If the governor is not using
+		devfreq-provided central polling
+		(/sys/class/devfreq/.../central_polling is 0), this value
+		may be useless.