Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753432Ab3GZJmp (ORCPT ); Fri, 26 Jul 2013 05:42:45 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:46578 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750793Ab3GZJmj (ORCPT ); Fri, 26 Jul 2013 05:42:39 -0400 Message-ID: <1374831744.2923.42.camel@shinybook.infradead.org> Subject: Re: [Ksummit-2013-discuss] DT bindings as ABI [was: Do we have people interested in device tree janitoring / cleanup?] From: David Woodhouse To: Richard Cochran Cc: Jason Gunthorpe , Mark Rutland , "devicetree@vger.kernel.org" , "ksummit-2013-discuss@lists.linuxfoundation.org" , Russell King - ARM Linux , 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 Date: Fri, 26 Jul 2013 10:42:24 +0100 In-Reply-To: <20130726080115.GA5436@netboy> 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> Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-aifDjmytBm7A/Y2251gl" X-Mailer: Evolution 3.8.4 (3.8.4-1.fc19) Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9812 Lines: 152 --=-aifDjmytBm7A/Y2251gl Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 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: > >=20 > > 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. >=20 > Think about what you just said. >=20 > 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. And the nodes in /chosen aren't describing hardware at all. Those are *absolutely* expected to be configuration things. It's quite normal for those to vary from one boot to the next, if your bootloader is sophisticated enough to do that. And if Jason wants to hard-code that kind of configuration data into his device-tree and ship it as part of the overall system image that gets installed, I see no particular problem with that. --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-aifDjmytBm7A/Y2251gl Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIISxDCCBjQw ggQcoAMCAQICAR4wDQYJKoZIhvcNAQEFBQAwfTELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0YXJ0 Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcxKTAn BgNVBAMTIFN0YXJ0Q29tIENlcnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTA3MTAyNDIxMDE1NVoX DTE3MTAyNDIxMDE1NVowgYwxCzAJBgNVBAYTAklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSsw KQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0ZSBTaWduaW5nMTgwNgYDVQQDEy9TdGFy 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