Intel Extensible Firmware Interface - Manual (Page 309)

Protocols — Console Support
Version 1.10 12/01/02 10-15
Status Codes Returned
EFI_SUCCESS The string was output to the device.
EFI_DEVICE_ERROR The device reported an error while attempting to output
the text.
EFI_UNSUPPORTED The output device’s mode is not currently in a defined
text mode.
EFI_WARN_UNKNOWN_GLYPH This warning code indicates that some of the characters
in the Unicode string could not be rendered and were
skipped.