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Date: Thu, 7 Nov 2013 14:22:05 -0800
From: Guenter Roeck <linux@roeck-us.net>
To: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>,
        Grant Likely <grant.likely@secretlab.ca>,
        Rob Herring <robherring2@gmail.com>,
        Stephen Warren <swarren@wwwdotorg.org>,
        Matt Porter <matt.porter@linaro.org>,
        Koen Kooi <koen@dominion.thruhere.net>,
        Alison Chaiken <Alison_Chaiken@mentor.com>,
        Dinh Nguyen <dinh.linux@gmail.com>, Jan Lubbe <jluebbe@lasnet.de>,
        Alexander Sverdlin <alexander.sverdlin@nsn.com>,
        Michael Stickel <ms@mycable.de>, Dirk Behme <dirk.behme@gmail.com>,
        Alan Tull <delicious.quinoa@gmail.com>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Michael Bohan <mbohan@codeaurora.org>,
        Ionut Nicu <ioan.nicu.ext@nsn.com>, Michal Simek <monstr@monstr.eu>,
        Matt Ranostay <mranostay@gmail.com>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3 - V2] Introducing Device Tree Overlays
Message-ID: <20131107222205.GA24450@roeck-us.net>
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On Thu, Nov 07, 2013 at 08:25:58PM +0100, Sebastian Andrzej Siewior wrote:
> On 06.11.13, Guenter Roeck wrote:
> |…
> thanks for the explanation.
> 
> > We use DT overlays to describe the hardware on those boards and, if necessary,
> > its configuration. For example, if there is a PCIe switch, the overlay would
> > describe its memory and bus number configuration.
> 
> So have your "fix" configuration and a few overlays you switch at
> runtime. The problem you have is that you want to switch a specific part
> if your configuration at runtime. I assume you run DT on ARM. What
> happens if you swtich from ARM to x86 and you "keep" your FPGA
> configuration requirement? You can't use both, DT and ACPI, right? So
> what happens then?
> 
We intend to use DT on x86 to augment ACPI data. There is a variety of reasons
why we can not use ACPI, nor do we want to as we prefer a single method for
handling OIR on all platforms. FWIW, the non-x86 platform is powerpc, not arm.

Guenter