serial: uniphier: flush transmitter before changing hardware settings

Ensure the transmitter is empty when chaining the baudrate or any
hardware settings. If a character is remaining in the transmitter,
the console will be garbled.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

drivers/serial/serial_uniphier.c

@@ -43,6 +43,10 @@ static int uniphier_serial_setbrg(struct udevice *dev, int baudrate)
 
 	divisor = DIV_ROUND_CLOSEST(priv->uartclk, mode_x_div * baudrate);
 
+	/* flush the trasmitter before changing hw setting */
+	while (!(readl(priv->membase + UNIPHIER_UART_LSR) & UART_LSR_TEMT))
+		;
+
 	writel(divisor, priv->membase + UNIPHIER_UART_DLR);
 
 	return 0;
@@ -132,6 +136,10 @@ static int uniphier_serial_probe(struct udevice *dev)
 
 	priv->uartclk = clk_data->clk_rate;
 
+	/* flush the trasmitter empty before changing hw setting */
+	while (!(readl(priv->membase + UNIPHIER_UART_LSR) & UART_LSR_TEMT))
+		;
+
 	tmp = readl(priv->membase + UNIPHIER_UART_LCR_MCR);
 	tmp &= ~UNIPHIER_UART_LCR_MASK;
 	tmp |= FIELD_PREP(UNIPHIER_UART_LCR_MASK, UART_LCR_WLEN8);