[PATCH 10/13] serial: stm32: fix FIFO flush in startup and set_termios

From: Erwan Le Ray
Date: Fri Feb 19 2021 - 12:51:37 EST


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@xxxxxxxxxxx>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index bdd7ca490021..45203648172b 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -657,7 +657,7 @@ 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);
@@ -762,8 +762,8 @@ 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)
--
2.17.1