linux-kernel - Re: [PATCH v2 00/16] ARM: support for ICP DAS LP-8x4x (with dts)

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Date:	Thu, 19 Dec 2013 01:20:46 +0400
From:	Sergei Ianovich <ynvich@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Daniel Mack <zonque@...il.com>,
	Haojian Zhuang <haojian.zhuang@...il.com>
Subject: Re: [PATCH v2 00/16] ARM: support for ICP DAS LP-8x4x (with dts)

On Wed, 2013-12-18 at 22:10 +0100, Arnd Bergmann wrote:
> On Wednesday 18 December 2013, Sergei Ianovich wrote:
> > Could we postpone this until someone needs this functionality?
> 
> We have to be sure that any device tree files you write now can remain
> compatible with future kernels if we add it later. My reasoning at first
> was that this wouldn't work if we had to change the "compatible" string
> for the bus node, but after re-thinking it now I believe that it's fine.

Great.

> You would still be able to boot a kernel with an old dts file on a new
> kernel if it just contains a "simple-bus" node here, as long as it doesn't
> need any boot-time setup at the bus controller. We can change the dts
> file later if we need to add this functionality, which would break booting
> old kernels with the new dts files, which isn't much of a problem in
> general.

It should actually only break old kernels which require new
functionally. Otherwise, dts can have

compatible = "marvell,pxa-extbus", "simple-bus";

and an older kernel will be happy with "simple-bus". Please correct me
if I'm wrong.


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