warp7: Set u-boot serial# based on OTP value

u-boot has a standard "serial#" environment variable that is suitable
for storing the iSerial number we will supply via the USB device
descriptor. serial# is automatically picked up by the disk subsystem in
u-boot - thus providing a handy unique identifier in /dev/disk/by-id as
detailed below.

Storing the hardware serial identifier in serial# means we can change the
serial# if we want before USB enumeration - thus making iSerial automatic
via OTP but overridable if necessary.

This patch reads the defined OTP fuse and sets environment variable
"serial#" to the value read.

With this patch in place the USB mass storage device will appear in
/dev/disk/by-id with a unique name based on the OTP value. For example

/dev/disk/by-id/usb-Linux_UMS_disk_0_WaRP7-0xf42400d3000001d4-0:0

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Rui Miguel Silva <rui.silva@linaro.org>
Cc: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>

board/warp7/warp7.c

@@ -23,6 +23,8 @@
 #include <power/pmic.h>
 #include <power/pfuze3000_pmic.h>
 #include "../freescale/common/pfuze.h"
+#include <asm/setup.h>
+#include <asm/bootm.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -186,6 +188,10 @@ int board_usb_phy_mode(int port)
 int board_late_init(void)
 {
 	struct wdog_regs *wdog = (struct wdog_regs *)WDOG1_BASE_ADDR;
+#ifdef CONFIG_SERIAL_TAG
+	struct tag_serialnr serialnr;
+	char serial_string[0x20];
+#endif
 
 	imx_iomux_v3_setup_multiple_pads(wdog_pads, ARRAY_SIZE(wdog_pads));
 
@@ -197,5 +203,13 @@ int board_late_init(void)
 	 */
 	clrsetbits_le16(&wdog->wcr, 0, 0x10);
 
+#ifdef CONFIG_SERIAL_TAG
+	/* Set serial# standard environment variable based on OTP settings */
+	get_board_serial(&serialnr);
+	snprintf(serial_string, sizeof(serial_string), "WaRP7-0x%08x%08x",
+		 serialnr.low, serialnr.high);
+	env_set("serial#", serial_string);
+#endif
+
 	return 0;
 }

include/configs/warp7.h

@@ -24,6 +24,9 @@
 #define CONFIG_SYS_FSL_ESDHC_HAS_DDR_MODE
 #define CONFIG_SYS_MMC_IMG_LOAD_PART	1
 
+/* Switch on SERIAL_TAG */
+#define CONFIG_SERIAL_TAG
+
 #define CONFIG_DFU_ENV_SETTINGS \
 	"dfu_alt_info=boot raw 0x2 0x400 mmcpart 1\0" \