tty/serial: atmel: fix out of range clock divider handling

Use MCK_DIV8 when the clock divider is > 65535. Unfortunately the mode
register was already written thus the clock selection is ignored.

Fix by doing the baud rate calulation before setting the mode.

Fixes: 5bf5635a ("tty/serial: atmel: add fractional baud rate support")
Signed-off-by: David Engraf <david.engraf@sysgo.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Acked-by: Richard Genoud <richard.genoud@gmail.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191216085403.17050-1-david.engraf@sysgo.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/atmel_serial.c

@@ -2270,27 +2270,6 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
 		mode |= ATMEL_US_USMODE_NORMAL;
 	}
 
-	/* set the mode, clock divisor, parity, stop bits and data size */
-	atmel_uart_writel(port, ATMEL_US_MR, mode);
-
-	/*
-	 * when switching the mode, set the RTS line state according to the
-	 * new mode, otherwise keep the former state
-	 */
-	if ((old_mode & ATMEL_US_USMODE) != (mode & ATMEL_US_USMODE)) {
-		unsigned int rts_state;
-
-		if ((mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_HWHS) {
-			/* let the hardware control the RTS line */
-			rts_state = ATMEL_US_RTSDIS;
-		} else {
-			/* force RTS line to low level */
-			rts_state = ATMEL_US_RTSEN;
-		}
-
-		atmel_uart_writel(port, ATMEL_US_CR, rts_state);
-	}
-
 	/*
 	 * Set the baud rate:
 	 * Fractional baudrate allows to setup output frequency more
@@ -2317,6 +2296,28 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
 
 	if (!(port->iso7816.flags & SER_ISO7816_ENABLED))
 		atmel_uart_writel(port, ATMEL_US_BRGR, quot);
+
+	/* set the mode, clock divisor, parity, stop bits and data size */
+	atmel_uart_writel(port, ATMEL_US_MR, mode);
+
+	/*
+	 * when switching the mode, set the RTS line state according to the
+	 * new mode, otherwise keep the former state
+	 */
+	if ((old_mode & ATMEL_US_USMODE) != (mode & ATMEL_US_USMODE)) {
+		unsigned int rts_state;
+
+		if ((mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_HWHS) {
+			/* let the hardware control the RTS line */
+			rts_state = ATMEL_US_RTSDIS;
+		} else {
+			/* force RTS line to low level */
+			rts_state = ATMEL_US_RTSEN;
+		}
+
+		atmel_uart_writel(port, ATMEL_US_CR, rts_state);
+	}
+
 	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
 	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);
 	atmel_port->tx_stopped = false;