mx51evk: Fix U-Boot corruption after saving the environment

U-Boot binary has grown in such a way that it goes beyond the reserved
area for the environment variables.

Running "saveenv" followed by a "reset" causes U-Boot to hang because
of this overlap.

Fix this problem by increasing the CONFIG_ENV_OFFSET size.

Also, in order to prevent this same problem to happen in the future,
use CONFIG_BOARD_SIZE_LIMIT, which will detect the overlap in build-time.

CONFIG_BOARD_SIZE_LIMIT does not accept math expressions, so declare
CONFIG_ENV_OFFSET with its direct value instead.

Signed-off-by: Fabio Estevam <festevam@gmail.com>

configs/mx51evk_defconfig

@@ -3,7 +3,7 @@ CONFIG_ARCH_MX5=y
 CONFIG_SYS_TEXT_BASE=0x97800000
 CONFIG_TARGET_MX51EVK=y
 CONFIG_ENV_SIZE=0x2000
-CONFIG_ENV_OFFSET=0x60000
+CONFIG_ENV_OFFSET=0xC0000
 CONFIG_NR_DRAM_BANKS=1
 # CONFIG_CMD_BMODE is not set
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx51evk/imximage.cfg"

include/configs/mx51evk.h

@@ -182,6 +182,19 @@
 /*-----------------------------------------------------------------------
  * environment organization
  */
+
+/*
+ * Environment starts at CONFIG_ENV_OFFSET=0xC0000 = 768k = 768 * 1024 = 786432
+ *
+ * Detect overlap between U-Boot image and environment area in build-time
+ *
+ * CONFIG_BOARD_SIZE_LIMIT = CONFIG_ENV_OFFSET - u-boot.imx offset
+ * CONFIG_BOARD_SIZE_LIMIT = 768k - 1k = 767k = 785408
+ *
+ * Currently CONFIG_BOARD_SIZE_LIMIT does not handle expressions, so
+ * write the direct value here
+ */
+#define CONFIG_BOARD_SIZE_LIMIT		785408
 #define CONFIG_SYS_MMC_ENV_DEV 0
 
 #endif