Index: sys/dev/uart/uart_dev_ns8250.c
===================================================================
--- sys/dev/uart/uart_dev_ns8250.c	(revision 255916)
+++ sys/dev/uart/uart_dev_ns8250.c	(working copy)
@@ -614,6 +614,7 @@ ns8250_bus_ipend(struct uart_softc *sc)
 
 	if (ns8250->busy_detect && (iir & IIR_BUSY) == IIR_BUSY) {
 		(void)uart_getreg(bas, DW_REG_USR);
+		wakeup(&ns8250->busy_detect);
 		uart_unlock(sc->sc_hwmtx);
 		return (0);
 	}
@@ -652,6 +653,16 @@ ns8250_bus_param(struct uart_softc *sc, int baudra
 
 	bas = &sc->sc_bas;
 	uart_lock(sc->sc_hwmtx);
+       /*
+	* When using DW UART with BUSY detection it is necessary to wait
+	* until all serial transfers are finished before manipulating the
+	* line control. LCR will not be affected when UART is busy.
+	*/
+	while (ns8250->busy_detect && 
+	    (uart_getreg(bas, DW_REG_USR) & USR_BUSY) == 0) {
+		msleep(&ns8250->busy_detect, sc->sc_hwmtx, "dwbusy", 10);
+	}
+
 	error = ns8250_param(bas, baudrate, databits, stopbits, parity);
 	uart_unlock(sc->sc_hwmtx);
 	return (error);