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FAILED: patch "[PATCH] tty: serial: lpuart: only disable CTS instead of overwriting" failed to apply to 6.1-stable tree

PATCH [email protected] 1 participant 1 message Apr 3, 2025

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The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x e98ab45ec5182605d2e00114cba3bbf46b0ea27f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025040351-unbalance-hypocrite-ec8a@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e98ab45ec5182605d2e00114cba3bbf46b0ea27f Mon Sep 17 00:00:00 2001
From: Sherry Sun <[email protected]>
Date: Fri, 7 Mar 2025 14:54:46 +0800
Subject: [PATCH] tty: serial: lpuart: only disable CTS instead of overwriting
the whole UARTMODIR register

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")
Cc stable <[email protected]>
Signed-off-by Sherry Sun <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Signed-off-by Greg Kroah-Hartman <[email protected]>
drivers/tty/serial/fsl_lpuart.c +7 -5
index c8cc0a241fba..33eeefa6fa8f 100644
@@ -2349,15 +2349,19 @@ 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),

@@ -2365,8 +2369,6 @@ 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 */