[PATCH] serial: imx: fix TX stop function not setting state to OFF in RS232-mode

[Robert Hodaszi <robert.hodaszi@xxxxxxxx>]

From: Robert Hodaszi <robert.hodaszi@xxxxxxxx>

If the mode had been changed to RS-485 after at least one character had
been sent in RS-232 mode, the RS-485 transmission was not working.

Commit cb1a609236096c278ecbfb7be678a693a70283f1 ("serial: imx: implement
rts delaying for rs485") added a TX state variable to keep track, when
it needs to enable / disable the RS-485 transmitter.

In RS-232 mode, the start TX function just sets the state to SEND, and
the stop function supposed to set it to OFF.

In RS-485 mode, the start TX function expects the state to be either
OFF, WAIT_AFTER_SEND, or WAIT_AFTER RTS. It cannot do anything if the
state is set to SEND, expects a stop first.

But stop TX function in RS-232 mode usually didn't set the state to OFF,
as it first checked if the shifter is empty, and if not, it just
returned, waiting for a TransmitComplete interrupt, which is only
enabled in RS-485 mode. So the stop function was never called again.

That check, and the subsequent code part is not needed for RS-232, it
just have to set the TX state to OFF.

Signed-off-by: Robert Hodaszi <robert.hodaszi@xxxxxxxx>
---
 drivers/tty/serial/imx.c | 46 +++++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 22 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 8257597d034d..511badce3edd 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -443,6 +443,12 @@ static void imx_uart_stop_tx(struct uart_port *port)
     ucr1 = imx_uart_readl(sport, UCR1);
     imx_uart_writel(sport, ucr1 & ~UCR1_TRDYEN, UCR1);

+    if (!(port->rs485.flags & SER_RS485_ENABLED)) {
+        /* Set the TX state in non-RS485 mode, nothing else to do */
+        sport->tx_state = OFF;
+        return;
+    }
+
     usr2 = imx_uart_readl(sport, USR2);
     if (!(usr2 & USR2_TXDC)) {
         /* The shifter is still busy, so retry once TC triggers */
@@ -453,33 +459,29 @@ static void imx_uart_stop_tx(struct uart_port *port)
     ucr4 &= ~UCR4_TCEN;
     imx_uart_writel(sport, ucr4, UCR4);

-    /* in rs485 mode disable transmitter */
-    if (port->rs485.flags & SER_RS485_ENABLED) {
-        if (sport->tx_state == SEND) {
-            sport->tx_state = WAIT_AFTER_SEND;
-            start_hrtimer_ms(&sport->trigger_stop_tx,
-                     port->rs485.delay_rts_after_send);
-            return;
-        }
+    if (sport->tx_state == SEND) {
+        sport->tx_state = WAIT_AFTER_SEND;
+        start_hrtimer_ms(&sport->trigger_stop_tx,
+                    port->rs485.delay_rts_after_send);
+        return;
+    }

-        if (sport->tx_state == WAIT_AFTER_RTS ||
-            sport->tx_state == WAIT_AFTER_SEND) {
-            u32 ucr2;
+    if (sport->tx_state == WAIT_AFTER_RTS ||
+        sport->tx_state == WAIT_AFTER_SEND) {
+        /* in rs485 mode disable transmitter */
+        u32 ucr2;

- hrtimer_try_to_cancel(&sport->trigger_start_tx);
+        hrtimer_try_to_cancel(&sport->trigger_start_tx);

-            ucr2 = imx_uart_readl(sport, UCR2);
-            if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
-                imx_uart_rts_active(sport, &ucr2);
-            else
-                imx_uart_rts_inactive(sport, &ucr2);
-            imx_uart_writel(sport, ucr2, UCR2);
+        ucr2 = imx_uart_readl(sport, UCR2);
+        if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
+            imx_uart_rts_active(sport, &ucr2);
+        else
+            imx_uart_rts_inactive(sport, &ucr2);
+        imx_uart_writel(sport, ucr2, UCR2);

-            imx_uart_start_rx(port);
+        imx_uart_start_rx(port);

-            sport->tx_state = OFF;
-        }
-    } else {
         sport->tx_state = OFF;
     }
 }
--
2.27.0