Proposal: new device-tree syntax and semantics for extendinginformation from included dts files

[David Gibson]

On Fri, Oct 15, 2010 at 09:10:55AM -0700, Stephen Neuendorffer wrote:
[snip]
> > > Why exactly?  Instead of being a stack of overlays, it seems to me
> like
> > > a stack of trees with operators..
> > > The point is exactly that operators make most sense at the stack of
> > > trees level and not
> > > at the individual node level.
> > 
> > I don't think I'm understanding what you're trying to say.  How do you
> differentiate "stack of
> > overlays" and "stack of trees"?
> > 
> > The reason I don't like this approach is that in many cases many
> > things will need to be changed by a single overlay, and not all those
> > changes will be the same operation.  For example, an overlay for a
> > board could add a bunch of nodes for i2c devices, and at the same time
> > remove an unused spi bus device.
> 
> So why not have two trees stacked to do the job? 
>  
> > The "stack of overlays" conceptual model that we've settled on uses
> > the concept that subsequent top level trees stack on top of the
> > preceding tree and can mask out or add/change nodes and properties.
> > The trees are merged together before going on to the next top level
> > tree.
> 
> I guess I'm stuck on 'overlay' to me implies '/extend/', so I associate
> the operations being on trees, not individual nodes.
> (Although, there's still the tough part about /remove-node/ vs
> /remove-property/,
> which might meant that the operations have to be in the trees to
> distinguish that).

I'm with Steve here, even though I still don't follow his reasoning
from here to the syntax he proposed earlier.  But I think we've
kind of moved past that option now, anyway.

There can be multiple overlays / top-level items per-file so there's
no reason the example above can't be done as multiple overlays with
different operaitons.

-- 
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