From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sascha Hauer Subject: Re: [RFC] [PATCH] Device Tree on ARM platform Date: Thu, 28 May 2009 17:04:09 +0200 Message-ID: <20090528150409.GO22742@pengutronix.de> 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> <20090528124307.GN22742@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-mnsaURCQ41sdnm+yROfE0A@public.gmane.org Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-mnsaURCQ41sdnm+yROfE0A@public.gmane.org To: Thomas Gleixner Cc: Russell King , devicetree-discuss , Mark Brown , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-xIg/pKzrS19vn6HldHNs0ANdhmdF6hFW@public.gmane.org, Scott Wood , Janboe Ye , Timur Tabi List-Id: devicetree@vger.kernel.org On Thu, May 28, 2009 at 03:18:02PM +0200, Thomas Gleixner wrote: > On Thu, 28 May 2009, Sascha Hauer wrote: > > > 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) > > Well, you can run it on 20+ PXA platforms which have all their own > machine number, but you have all the little details of each platform > hardcoded into the kernel. > > That does not help at all when your board has 5 variants just > different in subtle details which can not be probed or enumerated by > inspection. That's a common scenario in the embedded world. We normally hide these subtle details behind a baseboard= kernel parameter. I agree with you that it's far better to have a standardized way to specify this. For my taste the oftree is too bloated for this purpose. > > So you either have 5 board numbers and all the details harcoded again > or you add some extra magic to deduce on which variant you are running > on. > > We have seen almost everything in the weirdness range from poking in > some hardcoded FLASH cells over weird command line parsers up to a XML > parser which were added to work around the limitations of the machine > number model. > > With a device tree you can avoid that crap and provide a standardized > interface for such cases. > > I'm not saying that the device tree will make all those problems go > away magically, but it's orders of magnitudes better than what people > do now. > > There is no need to force switch all of ARM to the device tree, but > adding support for it would be a good move. Nobody wants to enforce it > and both models can live happily side by side and we'll see which > variant turns out to be the long term favourite solution. Having it as an optional feature seems a good idea for the same reasons you mentioned. I just wonder how optional it can be once a board maintainer and a person sending patches disagree on whether to use oftree or not. 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 |