ns8250_drain
ns8250_drain(bas, UART_DRAIN_TRANSMITTER);
ns8250_drain(bas, drain);
error = ns8250_drain(bas, what);
error = ns8250_drain(bas, UART_DRAIN_TRANSMITTER);
error = ns8250_drain(bas, UART_DRAIN_RECEIVER|UART_DRAIN_TRANSMITTER);