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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Erwan Le Ray <erwan.leray@foss.st.com>,
        Valentin Caron <valentin.caron@foss.st.com>
Subject: [PATCH 4.4 08/25] serial: stm32: fix software flow control transfer
Date:   Tue,  1 Feb 2022 19:16:32 +0100
Message-Id: <20220201180822.426450929@linuxfoundation.org>
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From: Valentin Caron <valentin.caron@foss.st.com>

commit 037b91ec7729524107982e36ec4b40f9b174f7a2 upstream.

x_char is ignored by stm32_usart_start_tx() when xmit buffer is empty.

Fix start_tx condition to allow x_char to be sent.

Fixes: 48a6092fb41f ("serial: stm32-usart: Add STM32 USART Driver")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20220111164441.6178-3-valentin.caron@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/serial/stm32-usart.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -279,7 +279,7 @@ static void stm32_start_tx(struct uart_p
 {
 	struct circ_buf *xmit = &port->state->xmit;
 
-	if (uart_circ_empty(xmit))
+	if (uart_circ_empty(xmit) && !port->x_char)
 		return;
 
 	stm32_set_bits(port, USART_CR1, USART_CR1_TXEIE | USART_CR1_TE);