Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755841Ab2KHN2p (ORCPT ); Thu, 8 Nov 2012 08:28:45 -0500 Received: from mail-wi0-f178.google.com ([209.85.212.178]:38198 "EHLO mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755644Ab2KHN2n convert rfc822-to-8bit (ORCPT ); Thu, 8 Nov 2012 08:28:43 -0500 Content-Type: text/plain; charset=US-ASCII Mime-Version: 1.0 (Mac OS X Mail 6.2 \(1499\)) Subject: Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap_devices to mach-omap2) From: Koen Kooi In-Reply-To: <509AE247.3000404@gmail.com> Date: Thu, 8 Nov 2012 14:28:39 +0100 Cc: Tabi Timur-B04825 , Grant Likely , Pantelis Antoniou , Rob Herring , Deepak Saxena , Benjamin Herrenschmidt , Wood Scott-B07421 , Tony Lindgren , Kevin Hilman , Matt Porter , linux-kernel , Felipe Balbi , Russ Dill , "linux-omap@vger.kernel.org" , "devicetree-discuss@lists.ozlabs.org" Content-Transfer-Encoding: 7BIT Message-Id: <356155A1-776B-4AA5-A912-14CE7D9AE42C@dominion.thruhere.net> References: <6AE080B68D46FC4BA2D2769E68D765B708174B7D@039-SN2MPN1-023.039d.mgd.msft.net> <509AE247.3000404@gmail.com> To: Ryan Mallon X-Mailer: Apple Mail (2.1499) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1960 Lines: 35 Op 7 nov. 2012, om 23:35 heeft Ryan Mallon het volgende geschreven: > On 06/11/12 08:40, Tabi Timur-B04825 wrote: >> On Mon, Nov 5, 2012 at 2:40 PM, Grant Likely wrote: >> >>> Jane is building custom BeagleBone expansion boards called 'capes'. She >>> can boot the system with a stock BeagleBoard device tree, but additional >>> data is needed before a cape can be used. She could replace the FDT file >>> used by U-Boot with one that contains the extra data, but she uses the >>> same Linux system image regardless of the cape, and it is inconvenient >>> to have to select a different device tree at boot time depending on the >>> cape. >> >> What's wrong with having the boot loader detect the presence of the >> Cape and update the device tree accordingly? We do this all the time >> in U-Boot. Doing stuff like reading EEPROMs and testing for the >> presence of hardware is easier in U-Boot than in Linux. > > This is probably okay for some hardware, but doesn't work in the general > case. Not all hardware is detectable, for example a cape which just adds > a set of LEDs for GPIO pins. Also, some hardware might not easily be > detectable without adding additional complexity to the boot loader. And as Pantelis mentioned before, I really don't want my users to change the bootloader whenever they add a new LED. Touching the bootloader is just too accident prone, we had a ton of RMA requests for older versions of the beagleboard from people trying to upgrade u-boot. Apart from the above I'd like to have fewer points of failure. Right now I need to keep uImage and foo.dtb in sync and I hate to add u-boot to that equasion as well. regards, Koen-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/