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:	Mon, 29 Jul 2013 22:35:03 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Richard Cochran <richardcochran@...il.com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Arend van Spriel <arend@...adcom.com>,
	Olof Johansson <olof@...om.net>,
	Mark Brown <broonie@...nel.org>,
	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 Mon, Jul 29, 2013 at 1:31 AM, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> Hi,
>
> On Sun, Jul 28, 2013 at 03:19:03PM +0200, Richard Cochran wrote:
>> On Sun, Jul 28, 2013 at 11:12:53AM +0200, Tomasz Figa wrote:
>>
>> > I'm not really sure what effect on users this has. Maybe you should define
>> > "users".
>>
>> ...
>>
>> > Care to explain this reasoning?
>>
>> Use Case
>> ~~~~~~~~
>>
>> User acquires a machine running ARM Linux version 3.x, with u-boot
>> and dtb in a read only flash partition. The board boots and works just
>> fine. However, for his application, the user requires a new kernel
>> feature that appeared in version 3.y where y > x. He compiles the new
>> kernel, and it also works.
>
> I'm afraid this kind of use case will never be properly supported, DT
> stable ABI or not.

Why? New kernel features should be no problem at all.

New driver features /might/ not be available, but only if the new
feature requires additional data that isn't present in the tree and
cannot be obtained elsewhere.

>
> Think about this: what kernel will actually be shipped in that board?
> Most likely, it will be a BSP kernel from the vendor. Does the vendor
> will have made that commitment to have a stable ABI for the DT? Will it
> use the same bindings than mainline? Do we want to support all the crazy
> bindings every vendor will come up with?

That's not a DT issue. That an out-of-tree board/SoC support issue. DT
doesn't make that any better or worse.

g.
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