[RFC][PATCH] Allow PReP boot loader to use OF calls

[Leigh Brown]

Well, if I had a penny...

> This patch, which applies on top of my OF boot loader changes patches,
> allows the PReP boot loader to use OF calls again.  I've implemented it
> slightly differently to the previous way, and I'll try to explain my
> rationale.
>
> The 140 (and presumably all PReP+OF boxes) comes up with machine check
> exceptions allowed and the exception table pointing to ram.
> Presumablythis is so that of functions can use interrupts and what not.
>  If a machine check or any other exception occurs on a prep+of box, the
> firmware will catch it and give you a nice easy to debug error message,
> and you can dump the registers and so on.  I get quite a few "hung
> trying to boot" reports so this would help me enormously.
>
> So, we want to keep this state as long as possible.  To achieve this, I
> just don't set it if we have OF (as opposed to switching it back and
> forward as was done the old way).  We absolutely must point the
> exception table to the ROM before we overwrite it so I do that just
> before the gunzip starts.


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