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

[Ian Campbell]

On Fri, 2016-07-29 at 11:49 +0200, Hans de Goede 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) {

Could/should this check be removed now? Or should sid[1]/sid[2] be
included?

> +#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.

I wonder if we should invert this, i.e. make it not use this new method
on all existing models. That would mean that all future models will
automatically use this new (IMHO better) scheme instead of requiring it
to be manually added each time (which we are sure to forget to do).

Main downside is the ifdef is going to be pretty long, but at least it
would be static. Maybe doing it with select in Kconfig (i.e. select
SUNXI_LEGACY_MAC_SID_THINGY on the existing platforms) would be a more
tollerable approach?

> > > > > > +		 */
> > +		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;