[PATCH] tty: serial: lpuart: only disable CTS instead of overwriting the whole UARTMODIR register

[PATCH] tty: serial: lpuart: only disable CTS instead of overwriting the whole UARTMODIR register

[Sherry Sun]

No need to overwrite the whole UARTMODIR register before waiting the
transmit engine complete, actually our target here is only to disable
CTS flow control to avoid the dirty data in TX FIFO may block the
transmit engine complete.
Also delete the following duplicate CTS disable configuration.

Fixes: d5a2e0834364 ("tty: serial: lpuart: disable flow control while waiting for the transmit engine to complete")
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
---
 drivers/tty/serial/fsl_lpuart.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 740de74e9f0a..e1350dac2f18 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -2347,15 +2347,19 @@ lpuart32_set_termios(struct uart_port *port, struct ktermios *termios,
 	/* update the per-port timeout */
 	uart_update_timeout(port, termios->c_cflag, baud);
 
+	/*
+	 * disable CTS to ensure the transmit engine is not blocked by the flow
+	 * control when there is dirty data in TX FIFO
+	 */
+	lpuart32_write(port, modem & ~UARTMODIR_TXCTSE, UARTMODIR);
+
 	/*
 	 * LPUART Transmission Complete Flag may never be set while queuing a break
 	 * character, so skip waiting for transmission complete when UARTCTRL_SBK is
 	 * asserted.
 	 */
-	if (!(old_ctrl & UARTCTRL_SBK)) {
-		lpuart32_write(port, 0, UARTMODIR);
+	if (!(old_ctrl & UARTCTRL_SBK))
 		lpuart32_wait_bit_set(port, UARTSTAT, UARTSTAT_TC);
-	}
 
 	/* disable transmit and receive */
 	lpuart32_write(port, old_ctrl & ~(UARTCTRL_TE | UARTCTRL_RE),
@@ -2363,8 +2367,6 @@ lpuart32_set_termios(struct uart_port *port, struct ktermios *termios,
 
 	lpuart32_write(port, bd, UARTBAUD);
 	lpuart32_serial_setbrg(sport, baud);
-	/* disable CTS before enabling UARTCTRL_TE to avoid pending idle preamble */
-	lpuart32_write(port, modem & ~UARTMODIR_TXCTSE, UARTMODIR);
 	/* restore control register */
 	lpuart32_write(port, ctrl, UARTCTRL);
 	/* re-enable the CTS if needed */
-- 
2.34.1

Re: [PATCH] tty: serial: lpuart: only disable CTS instead of overwriting the whole UARTMODIR register

[Greg KH]

On Fri, Mar 07, 2025 at 02:54:46PM +0800, Sherry Sun wrote:
> No need to overwrite the whole UARTMODIR register before waiting the
> transmit engine complete, actually our target here is only to disable
> CTS flow control to avoid the dirty data in TX FIFO may block the
> transmit engine complete.
> Also delete the following duplicate CTS disable configuration.
> 
> Fixes: d5a2e0834364 ("tty: serial: lpuart: disable flow control while waiting for the transmit engine to complete")
> Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
> ---
>  drivers/tty/serial/fsl_lpuart.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
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You are receiving this message because of the following common error(s)
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- You have marked a patch with a "Fixes:" tag for a commit that is in an
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If you wish to discuss this problem further, or you have questions about
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thanks,

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