From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e32.co.us.ibm.com (e32.co.us.ibm.com [32.97.110.150]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e32.co.us.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTP id 6117DDDE1D for ; Tue, 17 Jul 2007 12:28:12 +1000 (EST) Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e32.co.us.ibm.com (8.12.11.20060308/8.13.8) with ESMTP id l6H2MS6B005885 for ; Mon, 16 Jul 2007 22:22:28 -0400 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v8.4) with ESMTP id l6H2S97X205410 for ; Mon, 16 Jul 2007 20:28:09 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id l6H2S8gI027393 for ; Mon, 16 Jul 2007 20:28:08 -0600 Date: Mon, 16 Jul 2007 21:39:58 -0500 From: Josh Boyer To: Benjamin Herrenschmidt Subject: Re: [RFC][PATCH 6/8] Walnut DTS Message-ID: <20070717023957.GL3925@crusty.rchland.ibm.com> References: <1184161957.32199.52.camel@weaponx.rchland.ibm.com> <1184162389.32199.65.camel@weaponx.rchland.ibm.com> <4EAC985A-2F04-465D-AB69-C67807310D7B@kernel.crashing.org> <9696D7A991D0824DBA8DFAC74A9C5FA3030669AF@az33exm25.fsl.freescale.net> <28A3F6B9-512B-4D86-8E0D-A7680CCE2354@kernel.crashing.org> <1184622446.25235.89.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1184622446.25235.89.camel@localhost.localdomain> Cc: linuxppc-dev@ozlabs.org, Yoder Stuart-B08248 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Jul 17, 2007 at 07:47:26AM +1000, Benjamin Herrenschmidt wrote: > > That "typical practice" is inspired by the need to explicitly > > put #address-cells and #size-cells into the device tree if you > > want Linux to properly parse the device tree, even if the default > > values would work perfectly (if Linux would work correctly, > > that is). > > Linux does handle default values in some areas. The problem with default > values is that they are badly defined and the spec contains gray areas > and contradictions as to what the default values should be in some > circumstances. As a general matter, I dislike default values because > they somewhat require background knowledge of what default values should > be in different contexts to "read" a device-tree. To be simple, I > believe default values are a bad idea. Right. See, there are people like me that don't know what the default values are/should be. Having them explicitly listed, even if it's redundant, serves as a good learning aid. Now, realistically I do know what the default is in this case. But I only learned that recently. With hopefully more people starting to port things over to arch/powerpc it might be a good idea to document them at least. Otherwise, I fear we'd wind up repeating ourselves over and over. Could we get a 'thou shalt not rely on defaults' added to booting-without-of.txt? Or maybe something less draconian ;). josh