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 14:41:10 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Jason Cooper <jason@...edaemon.net>
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, 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.

-- 
dwmw2

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