serial8250_em485_start_tx
void serial8250_em485_start_tx(struct uart_8250_port *p, bool toggle_ier);
up->rs485_start_tx = serial8250_em485_start_tx;
up->rs485_start_tx = serial8250_em485_start_tx;
up.rs485_start_tx = serial8250_em485_start_tx;
EXPORT_SYMBOL_GPL(serial8250_em485_start_tx);