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: <20130726142140.GR24642@n2100.arm.linux.org.uk>
Date:	Fri, 26 Jul 2013 15:21:40 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"jonsmirl@...il.com" <jonsmirl@...il.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Jason Cooper <jason@...edaemon.net>,
	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>,
	Ian Campbell <ian.campbell@...rix.com>,
	Pawel Moll <Pawel.Moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Richard Cochran <richardcochran@...il.com>,
	Domenico Andreoli <cavokz@...il.com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	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 Fri, Jul 26, 2013 at 10:14:32AM -0400, jonsmirl@...il.com wrote:
> Yes, yes - that's why the schema should be written down and used as a
> validation input to dtc. Then dtc can spit out errors for non-standard
> items. There would be two versions - the standard one and a legacy one
> that includes the standard one plus the hacks that can't be undone.
> 
> But more importantly it provides a framework for people creating new
> node definitions. Now they can't work in a vacuum and come up with
> random names and structure for everything.
> 
> Most of the problems express in the thread would go away if the schema
> was written down and discussed. The rule going forward would be no new
> nodes that aren't part of the standard schema.

So this is why I'm seeing patches just a short time ago removing existing
compatible strings from the DT descriptions and associated driver, and
replacing them with new ones... meaning that the old DT files won't work
with newer kernels.

What that means is using the descriptions as the schema won't catch that
because they're changing those as well to match.

There's a solution to that: dtc becomes a separate project external to
the kernel which also contains the schemas that it verifies against.
That way, if you want to make changes such as that above, you need to
get it past not only kernel people but also past dtc maintainers -
which increases the chances of such stuff being caught.
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