From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ausmtp04.au.ibm.com (ausmtp04.au.ibm.com [202.81.18.152]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "ausmtp04.au.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTP id 76660DDD07 for ; Mon, 14 May 2007 10:25:01 +1000 (EST) Received: from sd0109e.au.ibm.com (d23rh905.au.ibm.com [202.81.18.225]) by ausmtp04.au.ibm.com (8.13.8/8.13.8) with ESMTP id l4E0itQM202008 for ; Mon, 14 May 2007 10:44:55 +1000 Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.250.243]) by sd0109e.au.ibm.com (8.13.8/8.13.8/NCO v8.3) with ESMTP id l4E0SVCL172724 for ; Mon, 14 May 2007 10:28:31 +1000 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id l4E0Ox9u005158 for ; Mon, 14 May 2007 10:24:59 +1000 Date: Mon, 14 May 2007 10:24:57 +1000 From: David Gibson To: Segher Boessenkool Subject: Re: [PATCH v2 6/7] Holly DTS Message-ID: <20070514002457.GD6517@localhost.localdomain> References: <20070509004948.GB4198@localhost.localdomain> <1178706570.3453.63.camel@zod.rchland.ibm.com> <0f60e44e6c7848e5eee8c82c0f2bfaec@kernel.crashing.org> <20070510235453.GD27188@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Cc: Olof Johansson , linuxppc-dev@ozlabs.org, Loeliger Jon-LOELIGER List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, May 12, 2007 at 02:02:42PM +0200, Segher Boessenkool wrote: > >>> What exactly did this ?? syntax imply? I must have missed that > >>> thread. > >> > >> A property in a DTS file can use that to say > >> the property should have a value, but it will > >> be filled in by the bootwrapper instead (memory > >> address/size, or network MAC address, for > >> instance). Presumably the kernel parser would > >> complain when it sees the this-is-still-undefined > >> marker. > >> > >> The original proposal specified the length of > >> the property value IIRC, but that isn't necessary > >> anymore. > > > > Well.. sort of. The first cut at the idea is that ? would be > > equivalent to zeroes in terms of dtc output, but would act as internal > > documentation that that property is supposed to be filled in by the > > bootloader. > > Yes. > > > Refinements to try to enforce that would be nice: > > Exactly my point. > > > easiest is to > > replace it with a configurable poison value. When using asm output, > > or with a map file, it might be possible to generate out-of-band > > information which we can use to check that the right things are filled > > in. > > > > It's not a simply a matter of making the kernel parser recognize the > > uninitialized info, because there's no way to encode that in the dtb > > itself. > > There can be, with a new DTB version -- perhaps simply > define proplen == -1 to mean "undefined" or similar. That doesn't quite do it, because I'd prefer ? to cover cases where the property's length is known, just not its value. In particular that could be useful for device trees where *only* non-moving edits are required by the bootloader, letting us use the asm output mode as intended. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson