If CONFIG_SERIAL_TERMIOS is not selected then non-consoles will do nothing. In order to restore legacy behavior you would have to do this: +#ifdef CONFIG_SERIAL_TERMIOS if ( -#ifdef CONFIG_SERIAL_TERMIOS dev->tc_iflag & ECHO -#else - dev->isconsole -#endif ) ... } +#endif That should eliminate the double character echo.So the command line tool has to do the different thing(echo or non echo by self) based on CONFIG_SERIAL_TERMIOS?
No, the legacy behavior is that the serial driver never echos by itself unless ECHO is selected.
