[U-Boot] [PATCH v2] sun8i: On H3 Use words 1-3 instead of just word 3 from the SID

[Hans de Goede]

It seems that bytes 13-14 of the SID / bytes 1-2 from word 3 of the SID
are always 0 on H3 making it a poor candidate to use as source for the
serialnr / mac-address, and the other non constant words (1 and 2) also
have quite a few bits which are the same for some boards,

This commits switches to using words 1 - 3 ex-or-ed together to get a
more unique value for the mac-address / serialnr.

Cc: Chen-Yu Tsai <wens at csie.org>
Cc: Corentin LABBE <clabbe.montjoie at gmail.com>
Cc: Amit Singh Tomar <amittomer25 at gmail.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
Changes in v2:
-ex-or all 3 words together instead of picking a different word
---
 board/sunxi/board.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/board/sunxi/board.c b/board/sunxi/board.c
index ef3fe26..e0734fb 100644
--- a/board/sunxi/board.c
+++ b/board/sunxi/board.c
@@ -623,6 +623,21 @@ static void setup_environment(const void *fdt)
 
 	ret = sunxi_get_sid(sid);
 	if (ret == 0 && sid[0] != 0 && sid[3] != 0) {
+#ifdef CONFIG_MACH_SUN8I_H3
+		/*
+		 * The single words 1 - 3 of the SID have quite a few bits
+		 * which are the same on many models on the H3, so we ex-or
+		 * them together to get a bit more unique value.
+		 *
+		 * Note we only do this on the H3 as we cannot change the
+		 * algorithm on other SoCs since those have been using
+		 * fixed mac-addresses based on only using word 3 for a
+		 * a long time and changing a fixed mac-address with an
+		 * u-boot update is not good.
+		 */
+		sid[3] ^= sid[1] ^ sid[2];
+#endif
+
 		/* Ensure the NIC specific bytes of the mac are not all 0 */
 		if ((sid[3] & 0xffffff) == 0)
 			sid[3] |= 0x800000;
-- 
2.7.4