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Subject: Re: [PATCH 15/16] Add device tree for Ebony
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
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Date: Thu, 15 Feb 2007 11:53:02 +1100
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Cc: linuxppc-dev@ozlabs.org, David Gibson <david@gibson.dropbear.id.au>
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> > Having it set to 0 provides the necessary definition so that the "right
> > hand" members of an interrupt map don't need a unit address in their
> > unit interrupt specifier.
> 
> And a missing #address-cells property means 0 for the
> purpose of interrupt mapping.  Here, have some quotes
> from the spec:
> 
> 
> > For nodes that represent devices, the number of cells to represent a 
> > unit interrupt specifier  is the  sum of the "#address-cells"  and 
> > "#interrupt-cells"  properties; for nodes that do  not represent 
> > devices, there is no relevant "#address-cells"  value, so that the 
> > number of cells  is solely determined by the "#interrupt-cells" value. 
> >  The latter case exists due to the nature of representing interrupt 
> > mapping outside the context of the normal device tree.
> 
> 
> > Note that the "open-pic" node does not have a "#address-cells" 
> > property, so that  the number of cells for the parent unit interrupt 
> > specifiers is 2 (which is the value of its "#interrupt-cells" 
> > property).
> 
> 
> > if present( "#address-cells", parent-node )
> > 	#cells = valueof( "#address-cells", parent-node )
> > else #cells = 0   then

Yes, "missing" is equivalent to 0, but the common practice has always
been to specify it explicitely. Check existing Apple and IBM
device-trees for example.

Ben.