linux-kernel - Re: [Ksummit-2013-discuss] DT bindings as ABI [was: Do we have people interested in device tree janitoring / cleanup?]

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Message-ID: <51F7EC84.90005@wwwdotorg.org>
Date:	Tue, 30 Jul 2013 10:40:36 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	David Gibson <david@...son.dropbear.id.au>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	"jonsmirl@...il.com" <jonsmirl@...il.com>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"ksummit-2013-discuss@...ts.linuxfoundation.org" 
	<ksummit-2013-discuss@...ts.linuxfoundation.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Ian Campbell <ian.campbell@...rix.com>,
	Pawel Moll <Pawel.Moll@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Richard Cochran <richardcochran@...il.com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Domenico Andreoli <cavokz@...il.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Dave P Martin <Dave.Martin@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Ksummit-2013-discuss] DT bindings as ABI [was: Do we have people
 interested in device tree janitoring / cleanup?]

On 07/29/2013 07:44 PM, David Gibson wrote:
...
> So, by way of investigation, let me propose an alternative
> expression of schemas, that I'm also not convinced we should do,
> but is possible and expressive.  It's illustrative, because it's
> kind of the polar opposite approach to XSD: just use C.

That actually sounds reasonable.

But, I think there's a difference between a schema, which defines
what's legal in an abstract fashion, and a validator, which defines
that the data conforms to the schema.

I can see that codding a validator in C would be pretty easy, and even
potentially quite simple/clean given a suitable set of library
functions as you say.

However, I'm not so convinced that expressing the schema itself as C
would work out so well. I think the code/data-structures would end up
being pretty stylized so they could actually be read as a schema. At
that point, a specific schema language would probably be simpler? Of
course, this is all somewhat conjecture; perhaps the only way to tell
would be to prototype various ideas and see how well they work.

Equally, I'm not sure I want to bind the schema definition to a
particular language. I'd like to be able to programatically generate
or manipulate *.dts files in arbitrary languages. Integrating a C
interpreter into those languages in order to handle the schema would
be annoying, whereas directly handling a special-purpose schema
language seems like it'd be more tangible.

As an aside, in the past I toyed with the idea of using Python data
structures as a *.dts syntax, and hence allowing
macros/auto-generation using custom Python code, and I'm sure Forth
will come up sometime in this thread:-)
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