serial_mxc: Fix setup of UARTx_UFCR register

This patch writes the default values for TXTL and RXTL to UARTx_UFCR.
Without this patch some older kernel versions crash as UARTx_UFCR was
not always correctly initialized.

Signed-off-by: Maximilian Schwerin <maximilian.schwerin@tigris.de>

drivers/serial/serial_mxc.c

@@ -75,6 +75,7 @@
 #define  UCR4_DREN	 (1<<0)  /* Recv data ready interrupt enable */
 #define  UFCR_RXTL_SHF   0       /* Receiver trigger level shift */
 #define  UFCR_RFDIV      (7<<7)  /* Reference freq divider mask */
+#define  UFCR_RFDIV_SHF  7      /* Reference freq divider shift */
 #define  UFCR_TXTL_SHF   10      /* Transmitter trigger level shift */
 #define  USR1_PARITYERR  (1<<15) /* Parity error interrupt flag */
 #define  USR1_RTSS	 (1<<14) /* RTS pin status */
@@ -135,6 +136,10 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
+#define TXTL  2 /* reset default */
+#define RXTL  1 /* reset default */
+#define RFDIV 4 /* divide input clock by 2 */
+
 static void mxc_serial_setbrg(void)
 {
 	u32 clk = imx_get_uartclk();
@@ -142,7 +147,9 @@ static void mxc_serial_setbrg(void)
 	if (!gd->baudrate)
 		gd->baudrate = CONFIG_BAUDRATE;
 
-	__REG(UART_PHYS + UFCR) = 4 << 7; /* divide input clock by 2 */
+	__REG(UART_PHYS + UFCR) = (RFDIV << UFCR_RFDIV_SHF)
+		| (TXTL << UFCR_TXTL_SHF)
+		| (RXTL << UFCR_RXTL_SHF);
 	__REG(UART_PHYS + UBIR) = 0xf;
 	__REG(UART_PHYS + UBMR) = clk / (2 * gd->baudrate);