Round the serial port clock divisor value returned by calc_divisor()

Round the serial port clock divisor value returned by
calc_divisor().

Signed-off-by: Hugo Villeneuve <hugo.villeneuve@lyrtech.com>
Signed-off-by: John Roberts <john.roberts@pwav.com>

drivers/serial/serial.c

@@ -144,8 +144,13 @@ static int calc_divisor (NS16550_t port)
 #else
 #define MODE_X_DIV 16
 #endif
-	return (CFG_NS16550_CLK / MODE_X_DIV / gd->baudrate);
 
+	/* Compute divisor value. Normally, we should simply return:
+	 *   CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate
+	 * but we need to round that value by adding 0.5 or 8/16.
+	 * Rounding is especially important at high baud rates.
+	 */
+	return (((16 * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate) + 8) / 16;
 }
 
 #if !defined(CONFIG_SERIAL_MULTI)