serial: stm32: fix FIFO flush in startup and set_termios

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>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 2bdd04a47f91723c9eccb1deac72283fb72d816a..183c76ddb1656481aae54005efc6e7f1e90cb932 100644 (file)
--- 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)