[RFC PATCH] dtc: Add support for named constants

[David Gibson]

On Tue, Aug 30, 2011 at 09:37:40AM -0700, Stephen Warren wrote:
> David Gibson wrote at Monday, August 29, 2011 10:23 PM:
> > On Tue, Aug 23, 2011 at 04:43:20PM -0600, Stephen Warren wrote:
> > > You may define constants as follows:
> > >
> > > /define/ $TWO 2;
> > > /define/ $FOUR 4;
> > > /define/ $OTHER $FOUR;
> > >
> > > And properties may use these values as follows:
> > >
> > > foo = <1 $TWO 3 $FOUR 5>;
> ...
> > > Note 2: I'd prefer the syntax of /define/ to be:
> > >
> > > /define/ TWO 2;
> > 
> > Oh goodness, yes.  The dollar signs are revolting.
> > 
> > > but I assume that'd cause the lexing for DT_DEFINEREF to conflict with
> > > that for DT_LABEL?
> > 
> > Nope, the final colon should distinguish DT_LABEL.  In dts-v1 C-like
> > identifiers should be lexically distinct in most contexts.  This is
> > not by accident.  They could be confused with node or property names,
> > but that shouldn't cause trouble.
> 
> OK, I'll take a stab at that and see.
> 
> As background, I found the following thread from 2008:
> 
> http://lists.ozlabs.org/pipermail/devicetree-discuss/2008-September/000149.html
> 
> ... where Jon Loeliger was working on much more extensive new syntax,
> and it sounded like you had some patches at least for math expressions
> in cells etc. The conversation seemed to die off after a few weeks. Did
> anything come of that; is anyone else working on e.g. at least the math
> expressions and defines part, even if not the scripting stuff?
> 
> I see that a little later, Jon pushed:
> 
> http://git.jdl.com/gitweb/?p=dtc.git;a=shortlog;h=refs/heads/testing
> 
> I'm mainly asking because if /any/ of that is something that's still
> useful to pursue, I might want to align this patch with some of that so
> as not to preclude any of that being ported to ToT.

Sigh, yeah.  So I think both Jon and I would really like to get rather
more comprehensive support for this sort of thing into dtc.  However,
we have somewhat different visions of how exactly it would work.  A
combination of that and lac of time to pursue it in depth lead to it
getting shelved at the time.

In the meantime the include and overlay mechanics have been introduced
which allow a limited amount of what people are askinf for in this
area.  Resurrecting that work of Jon's would, amongst other things,
require some reconsideration of how it's affected by those features.

-- 
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