Subject: [Ksummit-2013-discuss] DT bindings as ABI [was: Do we have people interested in device tree janitoring / cleanup?]

From: [email-masked] (Rob Herring)
Date: Fri, 26 Jul 2013 11:36:13 -0500

On 07/26/2013 10:49 AM, Olof Johansson wrote:
> On Fri, Jul 26, 2013 at 7:10 AM, Mark Brown <[email-masked]> wrote:
>> On Fri, Jul 26, 2013 at 03:09:29PM +0200, Richard Cochran wrote:
>>
>>> Unless I totally misunderstood, the thread is talking about letting
>>> established bindings change with each new kernel version.  I am
>>> opposed to that.
>>
>> No, nobody is really saying that is a particularly good idea.  There is
>> some debate about how we work out what an established binding is but
>> there's no serious suggestion that we don't want stable bindings.
> 
> Yes, what Mark said -- _today_ all bindings are subject to change and
> can be changed in lockstep with the kernel. This has been necessary as
> part of development to sort out all of the various bootstrapping
> issues across platforms.

This is absolutely not true on a global basis. Any binding used on
powerpc or sparc is not subject to change. Furthermore, there are ARM
platforms such as highbank where the bindings are expected to be stable.
That's not saying they don't change (new properties for SATA just
today), but they only change in a backwards compatible way.

Rob

> 
> What we're talking about is to end that mode of operation, and moving
> over to locking in bindings. Device tree contents, as mentioned
> elsewhere, might still be changed just like code is -- bugs are fixed,
> etc. But it's time to start locking down the bindings, in particular
> no longer change the established ones.
> 
> Long term, final goal is likely to be close to what Russell is saying
> -- nothing should go into the kernel tree unless the binding is in a
> fully stable state. However, we have a transitional period between now
> and then, and even when we're at the final state there will be need to
> have some sort of sandbox for development and test of future bindings.
> Dealing with all that, as well as the actual process for locking in
> bindings, is what needs to be sorted out.
> 
> I think we're all in agreement that bindings that change over time are
> nothing but pain, but we're arguing that in circles anyway.
> 
> 
> -Olof
>