The tester registers provide a unique chip-level identifier which
get_board_serial() returns in a "struct tag_serialnr".

This patch documents the properties of the registers; in summary.

31:0 OCOTP_TESTER0 (most significant)
- FSL-wide unique, encoded LOT ID STD II/SJC CHALLENGE/ Unique ID

OCOTP_TESTER1 (least significant)
31:24
- The X-coordinate of the die location on the wafer/SJC CHALLENGE/ Unique
  ID
23:16
- The Y-coordinate of the die location on the wafer/SJC CHALLENGE/ Unique
  ID
15:11
- The wafer number of the wafer on which the device was fabricated/SJC
  CHALLENGE/ Unique ID
10:0
- FSL-wide unique, encoded LOT ID STD II/SJC CHALLENGE/ Unique ID

The 64 bits of data generate a unique serial number per-chip.

Signed-off-by: Bryan O'Donoghue <bryan.odonog...@linaro.org>
Cc: Fabio Estevam <fabio.este...@nxp.com>
Cc: Peng Fan <peng....@nxp.com>
Cc: Stefano Babic <sba...@denx.de>
---
 arch/arm/mach-imx/mx7/soc.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/arm/mach-imx/mx7/soc.c b/arch/arm/mach-imx/mx7/soc.c
index 1602585..fb92a26 100644
--- a/arch/arm/mach-imx/mx7/soc.c
+++ b/arch/arm/mach-imx/mx7/soc.c
@@ -202,6 +202,27 @@ int arch_misc_init(void)
 #endif
 
 #ifdef CONFIG_SERIAL_TAG
+/*
+ * OCOTP_TESTER
+ * i.MX 7Solo Applications Processor Reference Manual, Rev. 0.1, 08/2016
+ * OCOTP_TESTER describes a unique ID based on silicon wafer
+ * and die X/Y position
+ *
+ * OCOTOP_TESTER offset 0x410
+ * 31:0 fuse 0
+ * FSL-wide unique, encoded LOT ID STD II/SJC CHALLENGE/ Unique ID
+ *
+ * OCOTP_TESTER1 offset 0x420
+ * 31:24 fuse 1
+ * The X-coordinate of the die location on the wafer/SJC CHALLENGE/ Unique ID
+ * 23:16 fuse 1
+ * The Y-coordinate of the die location on the wafer/SJC CHALLENGE/ Unique ID
+ * 15:11 fuse 1
+ * The wafer number of the wafer on which the device was fabricated/SJC
+ * CHALLENGE/ Unique ID
+ * 10:0 fuse 1
+ * FSL-wide unique, encoded LOT ID STD II/SJC CHALLENGE/ Unique ID
+ */
 void get_board_serial(struct tag_serialnr *serialnr)
 {
        struct ocotp_regs *ocotp = (struct ocotp_regs *)OCOTP_BASE_ADDR;
-- 
2.7.4

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