regulator: add get_status()

Based on previous LKML discussions:

 * Update docs for regulator sysfs class attributes to highlight
   the fact that all current attributes are intended to be control
   inputs, including notably "state" and "opmode" which previously
   implied otherwise.

 * Define a new regulator driver get_status() method, which is the
   first method reporting regulator outputs instead of inputs.
   It can report on/off and error status; or instead of simply
   "on", report the actual operating mode.

For the moment, this is a sysfs-only interface, not accessible to
regulator clients.  Such clients can use the current notification
interfaces to detect errors, if the regulator reports them.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>

Documentation/ABI/testing/sysfs-class-regulator

@@ -4,8 +4,8 @@ KernelVersion:	2.6.26
 Contact:	Liam Girdwood <lrg@slimlogic.co.uk>
 Description:
 		Some regulator directories will contain a field called
-		state. This reports the regulator enable status, for
-		regulators which can report that value.
+		state. This reports the regulator enable control, for
+		regulators which can report that input value.
 
 		This will be one of the following strings:
 
@@ -14,16 +14,54 @@ Description:
 		'unknown'
 
 		'enabled' means the regulator output is ON and is supplying
-		power to the system.
+		power to the system (assuming no error prevents it).
 
 		'disabled' means the regulator output is OFF and is not
-		supplying power to the system..
+		supplying power to the system (unless some non-Linux
+		control has enabled it).
 
 		'unknown' means software cannot determine the state, or
 		the reported state is invalid.
 
 		NOTE: this field can be used in conjunction with microvolts
-		and microamps to determine regulator output levels.
+		or microamps to determine configured regulator output levels.
+
+
+What:		/sys/class/regulator/.../status
+Description:
+		Some regulator directories will contain a field called
+		"status". This reports the current regulator status, for
+		regulators which can report that output value.
+
+		This will be one of the following strings:
+
+			off
+			on
+			error
+			fast
+			normal
+			idle
+			standby
+
+		"off" means the regulator is not supplying power to the
+		system.
+
+		"on" means the regulator is supplying power to the system,
+		and the regulator can't report a detailed operation mode.
+
+		"error" indicates an out-of-regulation status such as being
+		disabled due to thermal shutdown, or voltage being unstable
+		because of problems with the input power supply.
+
+		"fast", "normal", "idle", and "standby" are all detailed
+		regulator operation modes (described elsewhere).  They
+		imply "on", but provide more detail.
+
+		Note that regulator status is a function of many inputs,
+		not limited to control inputs from Linux.  For example,
+		the actual load presented may trigger "error" status; or
+		a regulator may be enabled by another user, even though
+		Linux did not enable it.
 
 
 What:		/sys/class/regulator/.../type
@@ -58,7 +96,7 @@ Description:
 		Some regulator directories will contain a field called
 		microvolts. This holds the regulator output voltage setting
 		measured in microvolts (i.e. E-6 Volts), for regulators
-		which can report that voltage.
+		which can report the control input for voltage.
 
 		NOTE: This value should not be used to determine the regulator
 		output voltage level as this value is the same regardless of
@@ -73,7 +111,7 @@ Description:
 		Some regulator directories will contain a field called
 		microamps. This holds the regulator output current limit
 		setting measured in microamps (i.e. E-6 Amps), for regulators
-		which can report that current.
+		which can report the control input for a current limit.
 
 		NOTE: This value should not be used to determine the regulator
 		output current level as this value is the same regardless of
@@ -87,7 +125,7 @@ Contact:	Liam Girdwood <lrg@slimlogic.co.uk>
 Description:
 		Some regulator directories will contain a field called
 		opmode. This holds the current regulator operating mode,
-		for regulators which can report it.
+		for regulators which can report that control input value.
 
 		The opmode value can be one of the following strings:
 
@@ -101,7 +139,8 @@ Description:
 
 		NOTE: This value should not be used to determine the regulator
 		output operating mode as this value is the same regardless of
-		whether the regulator is enabled or disabled.
+		whether the regulator is enabled or disabled.  A "status"
+		attribute may be available to determine the actual mode.
 
 
 What:		/sys/class/regulator/.../min_microvolts