linux-kernel - [PATCH] tty: serial: fsl_lpuart: avoid checking for transfer complete when UARTCTRL_SBK is asserted in lpuart32_tx

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Message-Id: <20230323054415.20363-1-sherry.sun@nxp.com>
Date:   Thu, 23 Mar 2023 13:44:15 +0800
From:   Sherry Sun <sherry.sun@....com>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-imx@....com
Subject: [PATCH] tty: serial: fsl_lpuart: avoid checking for transfer complete when UARTCTRL_SBK is asserted in lpuart32_tx_empty

According to LPUART RM, Transmission Complete Flag becomes 0 if queuing
a break character by writing 1 to CTRL[SBK], so here need to avoid
checking for transmission complete when UARTCTRL_SBK is asserted,
otherwise the lpuart32_tx_empty may never get TIOCSER_TEMT.

Commit 2411fd94ceaa("tty: serial: fsl_lpuart: skip waiting for
transmission complete when UARTCTRL_SBK is asserted") only fix it in
lpuart32_set_termios(), here also fix it in lpuart32_tx_empty().

Fixes: 380c966c093e ("tty: serial: fsl_lpuart: add 32-bit register interface support")
Signed-off-by: Sherry Sun <sherry.sun@....com>
---
 drivers/tty/serial/fsl_lpuart.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index c974a1d88f88..3281e81e1723 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -863,11 +863,17 @@ static unsigned int lpuart32_tx_empty(struct uart_port *port)
 			struct lpuart_port, port);
 	unsigned long stat = lpuart32_read(port, UARTSTAT);
 	unsigned long sfifo = lpuart32_read(port, UARTFIFO);
+	unsigned long ctrl = lpuart32_read(port, UARTCTRL);
 
 	if (sport->dma_tx_in_progress)
 		return 0;
 
-	if (stat & UARTSTAT_TC && sfifo & UARTFIFO_TXEMPT)
+	/*
+	 * LPUART Transmission Complete Flag may never be set while queuing a break
+	 * character, so avoid checking for transmission complete when UARTCTRL_SBK
+	 * is asserted.
+	 */
+	if ((stat & UARTSTAT_TC && sfifo & UARTFIFO_TXEMPT) || ctrl & UARTCTRL_SBK)
 		return TIOCSER_TEMT;
 
 	return 0;
-- 
2.17.1