Index: ic/pluart.c
===================================================================
RCS file: /cvs/src/sys/dev/ic/pluart.c,v
diff -u -p -r1.14 pluart.c
--- ic/pluart.c	2 Jul 2022 08:50:42 -0000	1.14
+++ ic/pluart.c	8 Jul 2025 00:16:54 -0000
@@ -167,6 +167,8 @@ pluart_attach_common(struct pluart_softc
 {
 	int fifolen, fr, lcr, maj;
 
+	mtx_init(&sc->sc_mtx, IPL_TTY);
+
 	if ((sc->sc_hwflags & COM_HW_SBSA) == 0) {
 		if (sc->sc_hwrev == 0)
 			sc->sc_hwrev = UART_PID2_REV(bus_space_read_4(sc->sc_iot,
@@ -255,13 +257,7 @@ pluart_intr(void *arg)
 	    !ISSET(is, UART_IMSC_TXIM))
 		return 0;
 
-	if (ISSET(is, UART_IMSC_TXIM) && ISSET(tp->t_state, TS_BUSY)) {
-		CLR(tp->t_state, TS_BUSY | TS_FLUSH);
-		if (sc->sc_halt > 0)
-			wakeup(&tp->t_outq);
-		(*linesw[tp->t_line].l_start)(tp);
-	}
-
+	mtx_enter(&sc->sc_mtx);
 	p = sc->sc_ibufp;
 
 	while (!ISSET(bus_space_read_4(iot, ioh, UART_FR), UART_FR_RXFE)) {
@@ -292,9 +288,21 @@ pluart_intr(void *arg)
 		/* XXX - msr stuff ? */
 	}
 	sc->sc_ibufp = p;
+	mtx_leave(&sc->sc_mtx);
 
 	softintr_schedule(sc->sc_si);
 
+	if (ISSET(is, UART_IMSC_TXIM)) {
+		KERNEL_LOCK();
+		if (ISSET(tp->t_state, TS_BUSY)) {
+			CLR(tp->t_state, TS_BUSY | TS_FLUSH);
+			if (sc->sc_halt > 0)
+				wakeup(&tp->t_outq);
+			(*linesw[tp->t_line].l_start)(tp);
+		}
+		KERNEL_UNLOCK();
+	}
+
 	return 1;
 }
 
@@ -493,19 +501,23 @@ pluart_softint(void *arg)
 	u_int16_t *ibufend;
 	int c;
 	int err;
-	int s;
 
-	if (sc == NULL || sc->sc_ibufp == sc->sc_ibuf)
+	if (sc == NULL)
+		return;
+
+	mtx_enter(&sc->sc_mtx);
+	if (sc->sc_ibufp == sc->sc_ibuf) {
+		mtx_leave(&sc->sc_mtx);
 		return;
+	}
 
 	tp = sc->sc_tty;
-	s = spltty();
 
 	ibufp = sc->sc_ibuf;
 	ibufend = sc->sc_ibufp;
 
 	if (ibufp == ibufend || tp == NULL || !ISSET(tp->t_state, TS_ISOPEN)) {
-		splx(s);
+		mtx_leave(&sc->sc_mtx);
 		return;
 	}
 
@@ -524,7 +536,7 @@ pluart_softint(void *arg)
 	}
 #endif
 
-	splx(s);
+	mtx_leave(&sc->sc_mtx);
 
 	while (ibufp < ibufend) {
 		c = *ibufp++;
Index: ic/pluartvar.h
===================================================================
RCS file: /cvs/src/sys/dev/ic/pluartvar.h,v
diff -u -p -r1.5 pluartvar.h
--- ic/pluartvar.h	27 Jun 2022 13:03:32 -0000	1.5
+++ ic/pluartvar.h	8 Jul 2025 00:16:54 -0000
@@ -58,6 +58,7 @@ struct pluart_softc {
 	u_int16_t		sc_ibufs[2][UART_IBUFSIZE];
 
 	struct clk	*sc_clk;
+	struct mutex	 sc_mtx;
 };
 
 void	pluart_attach_common(struct pluart_softc *, int);