serial: stm32: add FIFO flush when port is closed

[ 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@foss.st.com>
Link: https://lore.kernel.org/r/20210304162308.8984-12-erwan.leray@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 6788fb3af6cb98026f1bd0f7cbb72f29972d5e0c..cb8c2bece6d6e1174048796b5f2c62f454f9053e 100644 (file)
--- 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);