[PATCH 5.11 148/601] serial: stm32: fix incorrect characters on console

Greg Kroah-Hartman
2021-05-12T17:13:17Z

From: Erwan Le Ray <erwan.leray@foss.st.com>

[ Upstream commit f264c6f6aece81a9f8fbdf912b20bd3feb476a7a ]

Incorrect characters are observed on console during boot. This issue occurs
when init/main.c is modifying termios settings to open /dev/console on the
rootfs.

This patch adds a waiting loop in set_termios to wait for TX shift register
empty (and TX FIFO if any) before stopping serial port.

Fixes: 48a6092fb41f ("serial: stm32-usart: Add STM32 USART Driver")
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Link: https://lore.kernel.org/r/20210304162308.8984-4-erwan.leray@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/serial/stm32-usart.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 909a0d991ba1..70155e0c3b02 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -736,8 +736,9 @@ static void stm32_usart_set_termios(struct uart_port *port,
unsigned int baud, bits;
u32 usartdiv, mantissa, fraction, oversampling;
tcflag_t cflag = termios->c_cflag;
- u32 cr1, cr2, cr3;
+ u32 cr1, cr2, cr3, isr;
unsigned long flags;
+ int ret;

if (!stm32_port->hw_flow_control)
cflag &= ~CRTSCTS;
@@ -746,6 +747,15 @@ static void stm32_usart_set_termios(struct uart_port *port,

spin_lock_irqsave(&port->lock, flags);

+ ret = readl_relaxed_poll_timeout_atomic(port->membase + ofs->isr,
+ isr,
+ (isr & USART_SR_TC),
+ 10, 100000);
+
+ /* Send the TC error message only when ISR_TC is not set. */
+ if (ret)
+ dev_err(port->dev, "Transmission is not complete\n");
+
/* Stop serial port and reset value */
writel_relaxed(0, port->membase + ofs->cr1);

--
2.30.2