Re: [dtc PATCH V2] Warn on node name unit-address presence/absence mismatch

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

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On Fri, Sep 27, 2013 at 11:30:38AM +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2013-09-26 at 17:12 -0600, Stephen Warren wrote:
> > Well, ePAPR seems pretty specific that unit address and reg are
> > related,
> > but says nothing about ranges in the section on node naming, nor about
> > node naming in the section about ranges.
> > 
> > I'd claim that the existing PPC trees are nonconforming, and should be
> > fixed too:-)
> 
> This is tricky, we should probably fix ePAPR here.
> 
> If you have a "soc" bus covering a given range of addresses which it
> forwards to its children devices but doesn't have per-se its own
> registers in that area, then it wouldn't have a "reg" property. I would
> thus argue that in the absence of a "reg" property, if a "ranges" one is
> present, the "parent address" entry in there is an acceptable substitute
> for the "reg" property as far as unit addresses are concerned.

So, that's been accepted practice in fdt world for a while; I think
ePAPR already permits that, in fact.

> Also don't forget that in real OFW land, the unit address is something
> that's somewhat bus specific ... for example, PCI uses "dev,fn" rather
> than the full 96-bit number of the "reg" entry :-)
> 
> Another option which would more strictly conform to ePAPR and in fact to
> of1275 would be to require such bus nodes to have a "reg" property with
> the address value set to the beginning of the range and the size value
> set to 0 :-)
> 

-- 
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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