regulator_get_optional — obtain optional access to a regulator.
| struct regulator * regulator_get_optional ( | struct device * dev, | 
| const char * id ); | 
   Returns a struct regulator corresponding to the regulator producer,
   or IS_ERR condition containing errno.
   
   This is intended for use by consumers for devices which can have
   some supplies unconnected in normal use, such as some MMC devices.
   It can allow the regulator core to provide stub supplies for other
   supplies requested using normal regulator_get calls without
   disrupting the operation of drivers that can handle absent
   supplies.
   
   Use of supply names configured via regulator_set_device_supply is
   strongly encouraged.  It is recommended that the supply name used
   should match the name used for the supply and/or the relevant
   device pins in the datasheet.