[U-Boot] Update and Cut down mach types

[Wolfgang Denk <wd@denx.de>]

Dear Albert ARIBAUD,

In message <4DB72D4A.5070102@aribaud.net> you wrote:
>
> Well, as you stated yourself recently, why would/should we maintain 
> mach-types that are apparently not going to be used? Do machine types 
> have other uses than for Linux? No code in U-Boot should worry about the 
> mach-id if not for Linux.

Well, in principle you are of course right.

But I am well aware that there is a ton of Linux BSPs out there which
have never been pushed upstream into mainline by their respective
creators for some reason or another.  Also I see a chance that other
uses of the mach-ids might exist - the Linux ARM folks have, fro a
very long time, always explained what a clever idea this is to
describe hardware features.

I hesitate to cut off all these exitisting or even potential users
lightly, when there is a solution that works reasonably well for them
and, at the same time, brings only minimal maintenance burdon for us.

> Also, if we still decide to maintain our own list of mach-types, we will 
> need some rule to decide when to remove mach-types from this special 
> list eventually. Otherwise, it'll become asymptotically identical to the 
> full lits that is also availabe, and then, what would be the point of 
> maintaining our own?

That rule can be simple: we will only allow to add the now existing
(in U-Boot mainline code) mach-ids, so this list should not grow
further after the initial creation.  OK, ther eis a slight chance that
any newly added boards (to U-Boot) will get removed from the Linux
master file later, but I consider this a small risk - especially as I
expect to see more and ore device-tree based ARM ports quickly, so the
whole mach-id thing becomes less and less of a pain.

> So IMO, if we have mach-types in U-Boot for supporting Linux, then we 
> should keep using a (reasonably) up-to-date Linux machine ID list just 
> like we do now -- mach-types that disappear from the list mean Linux 
> support has become useless for that machine in U-Boot. And if we have 
> our own mach-type policy, different from "has linux support", then we 
> need to specify what this policy is and how it is implemented.

I think we should be gentle to users of existing code and avoid
breaking it. From now on, we could establish a policy that a mach-id
can only be referenced when and as long mainline Linux support for
this board exists.

I'm open for suggestions.

Best regards,

Wolfgang Denk

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