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

[Siarhei Siamashka]

On Fri, 29 Jul 2016 11:49:45 +0200
Hans de Goede <hdegoede at redhat.com> wrote:

> 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;

Using XOR is not a good idea, see my reply in the v1 patch discussion:
http://lists.denx.de/pipermail/u-boot/2016-July/262298.html

-- 
Best regards,
Siarhei Siamashka