Serial I/O Protocol
Version 1.02 12/12/00 221
Only the REQUEST_TO_SEND, DATA_TERMINAL_READY, HARDWARE_LOOPBACK_ENABLE,
SOFTWARE_LOOPBACK_ENABLE, and HARDWARE_FLOW_CONTROL_ENABLE bits can be set
with SetControl(). All the bits can be read with GetControl().
Status Codes Returned
EFI_SUCCESS The new control bits were set on the serial device.
EFI_UNSUPPORTED The serial device does not support this operation.
EFI_DEVICE_ERROR The serial device is not functioning correctly.