[PATCH 5.15 074/115] tty: serial: fsl_lpuart: skip waiting for transmission complete when UARTCTRL_SBK is asserted

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From: Sherry Sun <sherry.sun@xxxxxxx>

commit 2411fd94ceaa6e11326e95d6ebf876cbfed28d23 upstream.

According to LPUART RM, Transmission Complete Flag becomes 0 if queuing
a break character by writing 1 to CTRL[SBK], so here need to skip
waiting for transmission complete when UARTCTRL_SBK is asserted,
otherwise the kernel may stuck here.
And actually set_termios() adds transmission completion waiting to avoid
data loss or data breakage when changing the baud rate, but we don't
need to worry about this when queuing break characters.

Signed-off-by: Sherry Sun <sherry.sun@xxxxxxx>
Cc: stable <stable@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230223093941.31790-1-sherry.sun@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/tty/serial/fsl_lpuart.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -2201,9 +2201,15 @@ lpuart32_set_termios(struct uart_port *p
 	/* update the per-port timeout */
 	uart_update_timeout(port, termios->c_cflag, baud);
 
-	/* wait transmit engin complete */
-	lpuart32_write(&sport->port, 0, UARTMODIR);
-	lpuart32_wait_bit_set(&sport->port, UARTSTAT, UARTSTAT_TC);
+	/*
+	 * 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(&sport->port, 0, UARTMODIR);
+		lpuart32_wait_bit_set(&sport->port, UARTSTAT, UARTSTAT_TC);
+	}
 
 	/* disable transmit and receive */
 	lpuart32_write(&sport->port, old_ctrl & ~(UARTCTRL_TE | UARTCTRL_RE),





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