[PATCH] tty: serial: fsl_lpuart: make sure to turn off break before enabling CTS

[Sherry Sun]

Due to one LPUART IP bug which treat the CTS as higher priority than the
break signal, that cause the break signal sending through UARTCTRL_SBK
may impacted by the CTS input if the HW flow control is enabled.

So commit c4c81db5cf8b ("tty: serial: fsl_lpuart: disable the CTS when
send break signal") try to workaround this IP issue, it disables CTS
before asserting SBK to avoid any interference from CTS, and re-enable
it when break off.

Here we enable CTS before turning off the break, there is still a risk
of the break signal been impacted by CTS input. The correct sequence is
to disable CTS before asserting SBK, and re-enable CTS after break off,
which ensures the break signal won't be impacted by CTS, so fix it.

Fixes: c4c81db5cf8b ("tty: serial: fsl_lpuart: disable the CTS when send break signal")
Signed-off-by: Sherry Sun <sherry.sun@xxxxxxx>
---
 drivers/tty/serial/fsl_lpuart.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 0e56fa64b4ce..d9e46f7b80e5 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1550,20 +1550,19 @@ static void lpuart32_break_ctl(struct uart_port *port, int break_state)
 	modem = lpuart32_read(port, UARTMODIR);
 
 	if (break_state != 0) {
-		temp |= UARTCTRL_SBK;
 		/*
 		 * LPUART CTS has higher priority than SBK, need to disable CTS before
 		 * asserting SBK to avoid any interference if flow control is enabled.
 		 */
 		if (cflag & CRTSCTS && modem & UARTMODIR_TXCTSE)
 			lpuart32_write(port, modem & ~UARTMODIR_TXCTSE, UARTMODIR);
+		lpuart32_write(port, temp | UARTCTRL_SBK, UARTCTRL);
 	} else {
-		/* Re-enable the CTS when break off. */
+		lpuart32_write(port, temp, UARTCTRL);
+		/* Re-enable the CTS after break off. */
 		if (cflag & CRTSCTS && !(modem & UARTMODIR_TXCTSE))
 			lpuart32_write(port, modem | UARTMODIR_TXCTSE, UARTMODIR);
 	}
-
-	lpuart32_write(port, temp, UARTCTRL);
 }
 
 static void lpuart_setup_watermark(struct lpuart_port *sport)
-- 
2.17.1