From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761537AbZE1MnY (ORCPT ); Thu, 28 May 2009 08:43:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755727AbZE1MnR (ORCPT ); Thu, 28 May 2009 08:43:17 -0400 Received: from metis.ext.pengutronix.de ([92.198.50.35]:48023 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756073AbZE1MnO (ORCPT ); Thu, 28 May 2009 08:43:14 -0400 Date: Thu, 28 May 2009 14:43:07 +0200 From: Sascha Hauer To: Grant Likely Cc: Mark Brown , Russell King , devicetree-discuss , linux-kernel@vger.kernel.org, Timur Tabi , Scott Wood , Janboe Ye , linux-arm-kernel@lists.arm.linux.org.uk Subject: Re: [RFC] [PATCH] Device Tree on ARM platform Message-ID: <20090528124307.GN22742@pengutronix.de> Mail-Followup-To: Grant Likely , Mark Brown , Russell King , devicetree-discuss , linux-kernel@vger.kernel.org, Timur Tabi , Scott Wood , Janboe Ye , linux-arm-kernel@lists.arm.linux.org.uk References: <20090527150527.GK6805@pengutronix.de> <87vdnm8sec.fsf@macbook.be.48ers.dk> <4A1D6901.2090508@freescale.com> <20090527175609.GB31861@flint.arm.linux.org.uk> <4A1D8FBA.6040802@freescale.com> <20090527192909.GA32398@flint.arm.linux.org.uk> <20090527205218.GA5591@sirena.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Sent-From: Pengutronix Entwicklungszentrum Nord - Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Impressum: Pengutronix - Linux Solutions for Science and Industry Handelsregister: Amtsgericht Hildesheim, HRA 2686 Peiner Strasse 6-8, 31137 Hildesheim, Germany Phone: +49-5121-206917-0 | Fax: +49-5121-206917-5555 Inhaber: Dipl.-Ing. Robert Schwebel X-Message-Flag: See Message Headers for Impressum X-Uptime: 14:39:19 up 17 days, 3:03, 29 users, load average: 0.15, 0.14, 0.18 User-Agent: Mutt/1.5.18 (2008-05-17) X-SA-Exim-Connect-IP: 2001:6f8:1178:2:215:17ff:fe12:23b0 X-SA-Exim-Mail-From: sha@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 27, 2009 at 03:05:58PM -0600, Grant Likely wrote: > On Wed, May 27, 2009 at 2:52 PM, Mark Brown > wrote: > > On Wed, May 27, 2009 at 08:29:10PM +0100, Russell King wrote: > >> On Wed, May 27, 2009 at 02:08:42PM -0500, Scott Wood wrote: > > > >> > I'm not talking about platform specific code, I'm talking about code to > >> > retrieve information about a device from the device tree.  There would > >> > not be separate instances of this for "platforms X, Y and Z", just one > >> > of_platform binding in each driver.  It's no different than having a > >> > platform bus binding, except in the data structures used. > > > >> I really don't see what OF buys us then, apart from additional dependencies > >> that have to be correct for the kernel to work.  I can only see disadvantages > >> if all OF is, is a way to pass some file to the kernel to (effectively) tell > >> it which drivers to use. > > > > The main selling points of the device tree AFAICT are that some > > platforms have to use it it anyway due to the native OS and firmware for > > the platform use it, the possibility of using the same device tree with > > more than one OS (modulo unrepresentable holes) and the fact that some > > people find it more convenient to use than straight data tables > > (personally I find the two approaches to be much of a muchness there). > > Perhaps I'm missing something, though? > > Here are some that I've find useful: > > There is the advantage that it decouples the machine description from > the kernel code, which in turn seems to encourage code reuse. There > has been a significant decrease in the amount of platform specific > code in powerpc since the switch to FDT booting. > > There is the advantage of easy multiplatform support. I regularly > build a single kernel image which boots on all my MPC5200 boards, and > on my MPC83xx boards. That is not necessarily an advantage of a device tree. On ARM you can also build a kernel which runs on 20+ PXA platforms at the same time. (And I'm sure it can be done to even support say i.MX and PXA at the same time, but this is another story) Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |