From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Kerr Subject: Re: Boot interface for device trees on ARM Date: Wed, 19 May 2010 16:50:53 +0800 Message-ID: <201005191650.55978.jeremy.kerr@canonical.com> References: <201005181054.32325.jeremy.kerr@canonical.com> <20100518084954.GC25892@yookeroo> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org To: devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Cc: nicolas.pitre-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Nicolas Pitre List-Id: devicetree@vger.kernel.org Nicolas, > Exact. For example, on ARM the machine ID is also used to figure out > the MMU mapping needed to be able to simply be able to debug the very > early assembly boot stage when there isn't even a stack available. I get the impression that this is the only thing that we need the io_pg_offset for - setting up the debug page mapping, for very early printk output. If this is the case, I would much rather have it as a compile-time constant when doing this early debug; this is what I have been doing for DT boot in my tree (however, I would like to move it to something more configurable). In the cases where we need to debug the pre-C stuff (ie, machine bringup), I think we can live with a compile-time constant, rather than having to define a special 'exception' in the DT boot interface to handle this. Or is there another early use of the mdesc that I'm not aware of? Cheers, Jeremy