serial: mxs-auart: Fix baudrate calculation

commit a6040bc6 upstream.

The reference manual for the i.MX28 recommends to calculate the divisor
as

	divisor = (UARTCLK * 32) / baud rate, rounded to the nearest integer

, so let's do this. For a typical setup of UARTCLK = 24 MHz and baud
rate = 115200 this changes the divisor from 6666 to 6667 and so the
actual baud rate improves from 115211.521 Bd (error ≅ 0.01 %) to
115194.240 Bd (error ≅ 0.005 %).
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/tty/serial/mxs-auart.c

@@ -661,7 +661,7 @@ static void mxs_auart_settermios(struct uart_port *u,
 	baud_min = DIV_ROUND_UP(u->uartclk * 32, AUART_LINECTRL_BAUD_DIV_MAX);
 	baud_max = u->uartclk * 32 / AUART_LINECTRL_BAUD_DIV_MIN;
 	baud = uart_get_baud_rate(u, termios, old, baud_min, baud_max);
-	div = u->uartclk * 32 / baud;
+	div = DIV_ROUND_CLOSEST(u->uartclk * 32, baud);
 	ctrl |= AUART_LINECTRL_BAUD_DIVFRAC(div & 0x3F);
 	ctrl |= AUART_LINECTRL_BAUD_DIVINT(div >> 6);