[PATCH 5/5] serial: stm32: add RX and TX FIFO flush

[Erwan Le Ray]

Adds a flush of RX and TX FIFOs, and fixes some errors:
- adds RX FIFO flush in startup fonction
- removes the useless transmitter enabling in startup fonction
  (e.g. receiver only, see Documentation/serial/driver)
- configures FIFO threshold before enabling it, rather than after
- flushes both TX and RX in set_termios function

Signed-off-by: Erwan Le Ray <erwan.le...@st.com>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 4083145..21dc380 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -602,11 +602,11 @@ static int stm32_startup(struct uart_port *port)
        if (ret)
                return ret;
 
-       val = stm32_port->cr1_irq | USART_CR1_TE | USART_CR1_RE;
-       if (stm32_port->fifoen)
-               val |= USART_CR1_FIFOEN;
-       stm32_set_bits(port, ofs->cr1, val);
+       /* RX FIFO Flush */
+       if (ofs->rqr != UNDEF_REG)
+               stm32_set_bits(port, ofs->rqr, USART_RQR_RXFRQ);
 
+       /* Tx and RX FIFO configuration */
        if (stm32_port->fifoen) {
                val = readl_relaxed(port->membase + ofs->cr3);
                val &= ~(USART_CR3_TXFTCFG_MASK | USART_CR3_RXFTCFG_MASK);
@@ -615,6 +615,12 @@ static int stm32_startup(struct uart_port *port)
                writel_relaxed(val, port->membase + ofs->cr3);
        }
 
+       /* RX FIFO enabling */
+       val = stm32_port->cr1_irq | USART_CR1_RE;
+       if (stm32_port->fifoen)
+               val |= USART_CR1_FIFOEN;
+       stm32_set_bits(port, ofs->cr1, val);
+
        return 0;
 }
 
@@ -697,8 +703,12 @@ static void stm32_set_termios(struct uart_port *port, 
struct ktermios *termios,
        /* Stop serial port and reset value */
        writel_relaxed(0, port->membase + ofs->cr1);
 
-       cr1 = USART_CR1_TE | USART_CR1_RE;
+       /* flush RX & TX FIFO */
+       if (ofs->rqr != UNDEF_REG)
+               stm32_set_bits(port, ofs->rqr,
+                              USART_RQR_TXFRQ | USART_RQR_RXFRQ);
 
+       cr1 = USART_CR1_TE | USART_CR1_RE;
        if (stm32_port->fifoen)
                cr1 |= USART_CR1_FIFOEN;
        cr2 = 0;
-- 
1.9.1