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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Date:	Fri, 26 Jul 2013 10:39:37 -0400
From:	"jonsmirl@...il.com" <jonsmirl@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
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 10:21 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> 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.

I don't see that it has to be outside of the kernel. It could still be
inside and just have different maintainers.

The real value of having that schema inside of the kernel is so that
people writing new drivers have some rules to look at. It would really
help in stopping 37 different descriptions of DMA controllers that are
all slightly different. You'd have to match you DMA controller
description to the generic form or making a convincing argument as to
why you need the master schema to be changed.



-- 
Jon Smirl
jonsmirl@...il.com
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