twl4030_charger: enable manual enable/disable of usb charging.

'off' or 'auto' to

 /sys/class/power/twl4030_usb/mode

will now enable or disable charging from USB port.  Normally this is
enabled on 'plug' and disabled on 'unplug'.
Unplug will still disable charging.  'plug' will only enable it if
'auto' if selected.

Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
diff --git a/Documentation/ABI/testing/sysfs-class-power-twl4030 b/Documentation/ABI/testing/sysfs-class-power-twl4030
index 0331bba..40e0f91 100644
--- a/Documentation/ABI/testing/sysfs-class-power-twl4030
+++ b/Documentation/ABI/testing/sysfs-class-power-twl4030
@@ -13,3 +13,14 @@
 	Value can the set by writing to the attribute.
 	The change will only persist until the next
 	plug event.  These event are reported via udev.
+
+
+What: /sys/class/power_supply/twl4030_usb/mode
+Description:
+	Changing mode for USB port.
+	Writing to this can disable charging.
+
+	Possible values are:
+		"auto" - draw power as appropriate for detected
+			 power source and battery status.
+		"off"  - do not draw any power.