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

[Stephen Neuendorffer]

> -----Original Message-----
> From: Grant Likely [mailto:glikely at secretlab.ca] On Behalf Of Grant
Likely
> Sent: Friday, October 15, 2010 8:19 AM
> To: Stephen Neuendorffer
> Cc: David Gibson; John Bonesio; devicetree-discuss at lists.ozlabs.org
> Subject: Re: Proposal: new device-tree syntax and semantics for
extendinginformation from included dts
> files
> 
> On Thu, Oct 14, 2010 at 09:38:44AM -0700, Stephen Neuendorffer wrote:
> [fixed quoting header]
> > On Wed, Oct 13, 2010 5:46 PM, David Gibson wrote:
> > > On Wed, Oct 13, 2010 at 04:41:59PM -0700, Stephen Neuendorffer
wrote:
> > > [snip]
> > > > Or better yet, outside of the braces?
> [...]
> > > >             /remove/ {
> > > >  				serial at 2600 { };
// PSC4
> > > >
> > > >  				serial at 2800 { };
// PSC5
> > > >  		};
> > >
> > > Um.. no.  That makes even less sense in the conceptual framework
of a
> > > stack of overlays.
> >
> > 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.
> 
> g.
> 

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).

Steve

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