[PATCH 5.11 156/601] serial: stm32: fix FIFO flush in startup and set_termios

Greg Kroah-Hartman
2021-05-12T17:12:47Z

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

[ Upstream commit 315e2d8a125ad77a1bc28f621162713f3e7aef48 ]

Fifo flush set USART_RQR register by calling stm32_usart_set_bits
routine (Read/Modify/Write). USART_RQR register is a write only
register. So, read before write isn't correct / relevant to flush
the FIFOs.
Replace stm32_usart_set_bits call by writel_relaxed.

Fixes: 84872dc448fe ("serial: stm32: add RX and TX FIFO flush")
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Link: https://lore.kernel.org/r/20210304162308.8984-11-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 | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index a6295897c537..6788fb3af6cb 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -656,7 +656,7 @@ static int stm32_usart_startup(struct uart_port *port)

/* RX FIFO Flush */
if (ofs->rqr != UNDEF_REG)
- stm32_usart_set_bits(port, ofs->rqr, USART_RQR_RXFRQ);
+ writel_relaxed(USART_RQR_RXFRQ, port->membase + ofs->rqr);

/* RX enabling */
val = stm32_port->cr1_irq | USART_CR1_RE | BIT(cfg->uart_enable_bit);
@@ -760,8 +760,8 @@ static void stm32_usart_set_termios(struct uart_port *port,

/* flush RX & TX FIFO */
if (ofs->rqr != UNDEF_REG)
- stm32_usart_set_bits(port, ofs->rqr,
- USART_RQR_TXFRQ | USART_RQR_RXFRQ);
+ writel_relaxed(USART_RQR_TXFRQ | USART_RQR_RXFRQ,
+ port->membase + ofs->rqr);

cr1 = USART_CR1_TE | USART_CR1_RE;
if (stm32_port->fifoen)
--
2.30.2