[PATCH 5.10 141/530] serial: stm32: add FIFO flush when port is closed

[Greg Kroah-Hartman]

From: Erwan Le Ray <erwan.leray@xxxxxxxxxxx>

[ Upstream commit 9f77d19207a0e8ba814c8ceb22e90ce7cb2aef64 ]

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@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210304162308.8984-12-erwan.leray@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/tty/serial/stm32-usart.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 6788fb3af6cb..cb8c2bece6d6 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -689,6 +689,11 @@ static void stm32_usart_shutdown(struct uart_port *port)
 	if (ret)
 		dev_err(port->dev, "transmission complete not set\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);
-- 
2.30.2