'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: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NNeilBrown <neil@brown.name>
Signed-off-by: NSebastian Reichel <sre@kernel.org>