[PATCH 11/13] serial: stm32: add FIFO flush when port is closed

[Erwan Le Ray]

Transmission complete error is sent when ISR_TC is not set. If port closure
is requested despite data in TDR / TX FIFO has not been sent (because of
flow control), ISR_TC is not set and error message is sent on port closure
but also when a new port is opened.

Flush the data when port is closed, so the error isn't printed twice upon
next port opening.

Fixes: 64c32eab6603 ("serial: stm32: Add support of TC bit status check")
Signed-off-by: Erwan Le Ray <erwan.leray at foss.st.com>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 45203648172b..dcc309fd5d2f 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -691,6 +691,11 @@ static void stm32_usart_shutdown(struct uart_port *port)
 	if (ret)
 		dev_err(port->dev, "Transmission is not complete\n");
 
+	/* flush RX & TX FIFO */
+	if (ofs->rqr != UNDEF_REG)
+		writel_relaxed(USART_RQR_TXFRQ | USART_RQR_RXFRQ,
+			       port->membase + ofs->rqr);
+
 	stm32_usart_clr_bits(port, ofs->cr1, val);
 
 	free_irq(port->irq, port);
-- 
2.17.1