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

From: David Gibson
Date: Fri Sep 27 2013 - 01:21:36 EST

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 | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!

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