Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758805Ab3GZNSq (ORCPT ); Fri, 26 Jul 2013 09:18:46 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:38691 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758009Ab3GZNSm (ORCPT ); Fri, 26 Jul 2013 09:18:42 -0400 Date: Fri, 26 Jul 2013 14:14:23 +0100 From: Russell King - ARM Linux To: Richard Cochran Cc: David Woodhouse , Jason Gunthorpe , Mark Rutland , "devicetree@vger.kernel.org" , "ksummit-2013-discuss@lists.linuxfoundation.org" , Pawel Moll , Stephen Warren , Domenico Andreoli , "rob.herring@calxeda.com" , "linux-kernel@vger.kernel.org" , Dave P Martin , "linux-arm-kernel@lists.infradead.org" , Ian Campbell Subject: Re: [Ksummit-2013-discuss] DT bindings as ABI [was: Do we have people interested in device tree janitoring / cleanup?] Message-ID: <20130726131423.GL24642@n2100.arm.linux.org.uk> References: <20130725175702.GC22291@e106331-lin.cambridge.arm.com> <51F168FC.9070906@wwwdotorg.org> <20130725182920.GA24955@e106331-lin.cambridge.arm.com> <20130725184834.GA8296@netboy> <20130725213753.GC17616@obsidianresearch.com> <20130726080115.GA5436@netboy> <1374831744.2923.42.camel@shinybook.infradead.org> <20130726130927.GC4219@netboy> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130726130927.GC4219@netboy> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2517 Lines: 52 On Fri, Jul 26, 2013 at 03:09:29PM +0200, Richard Cochran wrote: > On Fri, Jul 26, 2013 at 10:42:24AM +0100, David Woodhouse wrote: > > On Fri, 2013-07-26 at 10:01 +0200, Richard Cochran wrote: > > > On Thu, Jul 25, 2013 at 03:37:53PM -0600, Jason Gunthorpe wrote: > > > > > > > > We use DT has a kernel configuration input. Our environment is > > > > designed to guarantee 100% that the kernel and DT match exactly. DT > > > > very deliberately isn't an ABI boundary in our systems. > > > > > > Think about what you just said. > > > > > > The DT describes the *hardware* not the kernel. Why should you ever > > > need to update your DT at all? > > > > Well, the nodes which describe hardware devices, according to the > > bindings which form an ABI contract between DT and drivers, should not > > normally change. Although they *can* change, if for example you change > > the MAC address and that's stored there. Or you change the PHY you want > > it to use. Or something like that. The *ABI* doesn't change, but the > > data you express *using* that ABI can change. That's kind of the point. > > Unless I totally misunderstood, the thread is talking about letting > established bindings change with each new kernel version. I am > opposed to that. > > Of course, a user may want to change the values of his MAC addresses, > if he needs to. But he should never have to change *how* he specifies > those addresses. > > So, as long as everyone can agree to the principle that a working DT > should remain working after a kernel upgrade, then I'll shut up. In > actual fact, this is not the case today, nor was it ever so in the > past, AFAICT, but it never hurts to set goals. We agree. That's precisely why I'm saying that once a binding appears in a -final released kernel, it is _stable_ by that very fact. If there were any doubts about it, it should never have been accepted into the kernel tree in the first place. It's no different from how we treat syscalls. Once we accept a syscall and it's published in a -final kernel, it can't then be altered - it can be supplemented by a new syscall with a different interface, but the old one remains and keeps its semantics for a great many years. There's no reason for DT to be any different in this regard. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/