serial: imx: set_mctrl(): correctly restore autoRTS state

imx_uart_set_mctrl() happened to set UCR2_CTSC bit whenever TIOCM_RTS
was set, no matter if RTS/CTS handshake is enabled or not. Now fixed by
turning handshake on only when CRTSCTS bit for the port is set.

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/1564167161-3972-3-git-send-email-sorganov@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 14 insertions, 2 deletions

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 32f36d86a960..059ba354d17e 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -974,10 +974,22 @@ static void imx_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
         if (!(port->rs485.flags & SER_RS485_ENABLED)) {
                 u32 ucr2;
 
+                /*
+                 * Turn off autoRTS if RTS is lowered and restore autoRTS
+                 * setting if RTS is raised.
+                 */
                 ucr2 = imx_uart_readl(sport, UCR2);
                 ucr2 &= ~(UCR2_CTS | UCR2_CTSC);
-                if (mctrl & TIOCM_RTS)
-                        ucr2 |= UCR2_CTS | UCR2_CTSC;
+                if (mctrl & TIOCM_RTS) {
+                        ucr2 |= UCR2_CTS;
+                        /*
+                         * UCR2_IRTS is unset if and only if the port is
+                         * configured for CRTSCTS, so we use inverted UCR2_IRTS
+                         * to get the state to restore to.
+                         */
+                        if (!(ucr2 & UCR2_IRTS))
+                                ucr2 |= UCR2_CTSC;
+                }
                 imx_uart_writel(sport, ucr2, UCR2);
         }