Re: Some slightly random musings on device tree expression syntax

On Mon, Mar 12, 2012 at 08:53:05AM -0500, Jon Loeliger wrote:

quoted

I was thinking some more about how to expand the device tree syntax to
allow expressions.

Excellent!

quoted

I wondered if we should use a concept/syntax more
inspired by template processors. Playing with jinja2 and gpp led me
towards (...) being an inline expression syntax that can calculate
integers or strings and get replaced by the string representation of the
expression, and ! at the start of a line introducing a statement
context. So, below are my somewhat wandering thoughts on the matter.
However, the idea still raises a lot of questions that'd need to be
resolved.

I note a few things:

* Using the (...) syntax to indicate which parts of the file should be
evaluated and the substituted solves the issue that David had with Jon's
proposal re: how do you know when a node name is literal text vs.
concatenated to some expression.

So the M4 solution then.

Erm.. use of (...) to disambiguate expressions seems an independent
matter from whether we use m4 or a macro preprocessor versus
in-dtc-proper expression evaluation.

quoted

* As an aside, I wonder if we couldn't transparently allow <1 2 3> or
<1, 2, 3> for cell list syntax, thus not requiring the brackets in
previously proposed <(1 + 0) (1 + 1) (4 - 1)> syntax, but rather <1 + 0,
1 + 1, 4 - 1>?

That's the sort of direction I advocated earlier.

Hrm.  I don't think this is a good idea.  Having two different cell
list formats seems to me to encourage confusions for minimal benefit.
I think (...) will generally delimit expressions more readably anyway.
Especially since it would match using that syntax to distinguish
expressions in other places, like node or property names.

-- 
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