serial: imx: set_termios(): do not enable autoRTS if RTS is unset

Don't let receiver hardware automatically control RTS output if it
was requested to be inactive.

To ensure this, set_termios() shouldn't set UCR2_CTSC bit if UCR2_CTS
(=TIOCM_RTS) is cleared. Added corresponding check in imx_uart_rts_auto()
to fix this.
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Sergey Organov <sorganov@gmail.com>
Link: https://lore.kernel.org/r/1564167161-3972-2-git-send-email-sorganov@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -405,7 +405,12 @@ static void imx_uart_rts_inactive(struct imx_port *sport, u32 *ucr2)
 /* called with port.lock taken and irqs caller dependent */
 static void imx_uart_rts_auto(struct imx_port *sport, u32 *ucr2)
 {
-	*ucr2 |= UCR2_CTSC;
+	/*
+	 * Only let receiver control RTS output if we were not requested to have
+	 * RTS inactive (which then should take precedence).
+	 */
+	if (*ucr2 & UCR2_CTS)
+		*ucr2 |= UCR2_CTSC;
 }
 
 /* called with port.lock taken and irqs off */