serial: sh-sci: Avoid FIFO clear for MCE toggle.

When toggling the MCE support we don't want to concern ourselves with the
FIFO state, so ensure that the clearing bits are masked out when updating
the MCE state.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

drivers/tty/serial/sh-sci.c

@@ -1771,18 +1771,25 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
 
 	sci_init_pins(port, termios->c_cflag);
 
-	if (s->cfg->capabilities & SCIx_HAVE_RTSCTS) {
 	reg = sci_getreg(port, SCFCR);
 	if (reg->size) {
-			unsigned short ctrl;
+		unsigned short ctrl = sci_in(port, SCFCR);
 
-			ctrl = sci_in(port, SCFCR);
+		if (s->cfg->capabilities & SCIx_HAVE_RTSCTS) {
 			if (termios->c_cflag & CRTSCTS)
 				ctrl |= SCFCR_MCE;
 			else
 				ctrl &= ~SCFCR_MCE;
-			sci_out(port, SCFCR, ctrl);
 		}
+
+		/*
+		 * As we've done a sci_reset() above, ensure we don't
+		 * interfere with the FIFOs while toggling MCE. As the
+		 * reset values could still be set, simply mask them out.
+		 */
+		ctrl &= ~(SCFCR_RFRST | SCFCR_TFRST);
+
+		sci_out(port, SCFCR, ctrl);
 	}
 
 	sci_out(port, SCSCR, s->cfg->scscr);