Re: [PATCH] libfdt: add address translation support

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Mon, May 12, 2014 at 04:10:02PM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2014-05-12 at 16:00 +1000, David Gibson wrote:
> > I'm not all that impressed by this translation code - in particular
> > the per-bus-type hooks don't make sense to me.  AFAIK the
> > interpretation of ranges is not bus specific. I think it will also
> > fail in some cases with #address-cells > 2, which is unfortunate.
> > 
> > I'm about to post my own implementation of address translation.
> 
> Well, I came up with the original code which did per-bus type hooks.
> There are cases where it is needed.
> 
> Take PCI. The top word can contain completely unrelated stuff such
> as the "prefetchable" attribute.
> 
> It's perfectly legal to put a prefetchable BAR under a non-prefetchable
> bridge window.
> 
> However a translation scheme that doesn't know to know that bit
> will fail.
> 
> It's not far fetched, it happens on our machines today.
> 
> And that's just one of the problems I had back then...

Ah.  Bother.

I supposed it's arguable that a PCI ranges property really should have
windows for both prefetchable and non-prefetchable areas, but since
that's not done in practice, it's pretty much moot.

Ok, I'll need to rethink.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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