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

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Message-ID: <20130729184048.GE15861@obsidianresearch.com>
Date:	Mon, 29 Jul 2013 12:40:48 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	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>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Pawel Moll <Pawel.Moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	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>,
	Olof Johansson <olof@...om.net>,
	Dave P Martin <Dave.Martin@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Ian Campbell <ian.campbell@...rix.com>
Subject: Re: DT bindings as ABI [was: Do we have people interested in device
 tree janitoring / cleanup?]

On Mon, Jul 29, 2013 at 07:16:07PM +0100, Russell King - ARM Linux wrote:

> What does it take?  Good practice, care, thought and planning.  All
> the qualities which should already be present for kernel _engineers_.
> Not an "lets create something for me, I don't care about anyone else"
> attitude.

I agree with what you've written, but we are looking at this from
different ends of the problem.

I fully agree you can create a main line kernel GIT tree that has a
stable DT ABI.

However, I as an ODM, with time pressure, cannot wait for the kernel
folks to finish this work. So from my perspective the DT will not be
stable, as I will put whatever interm stuff I choose to have a
shippable product.

Thus I have to design my systems for an unstable DT, and the message
from the kernel community to people in my posistion should be:

  When you ship early with non-mainlined DT schema, design your boot
  system around an unstable DT. Plan to migrate your DT to upstream
  once it becomes finalized.

Here is the rub: Once I design for an unstable DT I simply don't
derive value from the kernel communities work to create a stable DT.

So who is getting the benefit of this work, and is it worth the cost?

Jason
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