From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH] scripts/dtc: pad DTBs to facilitate later modification Date: Thu, 29 May 2014 09:55:34 -0600 Message-ID: <53875876.2020001@wwwdotorg.org> References: <1400888507-11637-1-git-send-email-khilman@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1400888507-11637-1-git-send-email-khilman@linaro.org> Sender: linux-kbuild-owner@vger.kernel.org To: Kevin Hilman , linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org Cc: Arnd Bergmann , Olof Johansson , linaro-kernel@lists.linaro.org, Nicolas Pitre , Thomas Petazzoni , Michal Marek , "open list:KERNEL BUILD + fi..." , open list List-Id: devicetree@vger.kernel.org On 05/23/2014 05:41 PM, Kevin Hilman wrote: > By default, add some padding to the DT blobs to facilitate later > patching. > > An example need for DTB patching is the need to modifiy the command > line on platforms where ATAGS are not (or cannot) be used to pass the > commandline. For example, we do not support a big-endian kernel > reading ATAGS from a little-endian u-boot, so the only way to pass a > command line in the DT. > > Also, without ATAG support (or if u-boot was built without > CONFIG_INITRD_TAG) the only way to pass an initrd is by adding an > initrd= option to command line (in the DT). > > Therefore, to facilitate adding to the DT command line directly in the > DTB, add some padding. > > Cc: Nicolas Pitre > Cc: Stephen Warren > Cc: Thomas Petazzoni > Signed-off-by: Kevin Hilman > --- > I kinda pulled 64 bytes out of the air here since it's enough to add > some common things to the commandline like debug, earlyprink > initrd=,, etc., but I'm certainlly not opposed to more > padding. Conceptually, Acked-by: Stephen Warren But I would expect a pad of something like 4KB to be more future-proof. U-Boot appears to use 4KB on ARM at least: ./arch/arm/dts/Makefile:37:DTC_FLAGS += -R 4 -p 0x1000