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: <20130726134720.GJ29916@titan.lakedaemon.net>
Date:	Fri, 26 Jul 2013 09:47:20 -0400
From:	Jason Cooper <jason@...edaemon.net>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Richard Cochran <richardcochran@...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>,
	Stephen Warren <swarren@...dotorg.org>,
	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 02:41:10PM +0100, David Woodhouse wrote:
> On Fri, 2013-07-26 at 09:27 -0400, Jason Cooper wrote:
> > 
> > The other dynamic change that bears mentioning here is attributes which
> > have been configured by the bootloader.  For example, in mvebu, we have
> > the Schrodinger's Cat register.  It allows you to reconfigure the base
> > address of the registers from *within* that register range.  If the
> > bootloader does this, the DT needs to be updated to reflect the current
> > hardware configuration.  Otherwise, the kernel is stuck poking around at
> > memory addresses hoping to find something sane.
> > 
> > But this falls into the same category as you mentioned, but outside of
> > chosen {};.
> 
> Yeah, /chosen was given as an example of stuff that's almost
> *exclusively* "configuration" stuff.
> 
> But there's plenty outside there that can reasonably change.
> 
> It's OK to change the data, and of *course* the base address reported in
> the DT should actually match reality *today*, if it changes on the fly.
> 
> It's not OK to change the *schema*  in which those data are expressed.
> That's the ABI we're talking about.

Agreed, much more clear than what I was saying.

thx,

Jason.
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