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Subject: Re: [PATCH 0/3 - V2] Introducing Device Tree Overlays
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From: Pantelis Antoniou <panto@antoniou-consulting.com>
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Date: Thu, 7 Nov 2013 22:06:31 +0200
Cc: Guenter Roeck <linux@roeck-us.net>,
        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>,
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References: <1383676898-29819-1-git-send-email-panto@antoniou-consulting.com> <20131106190152.GA8662@breakpoint.cc> <20131106193041.GA26796@roeck-us.net> <20131106203821.GC8662@breakpoint.cc> <20131106211754.GA29300@roeck-us.net> <20131107192558.GA11453@breakpoint.cc>
To: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
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Hi Sebastian,

On Nov 7, 2013, at 9:25 PM, 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?
> 

FWIW DT has been ported to x86. And is present on arm/powerpc/mips/arc and possibly
others.

So what are we talking about again? If you care about the non-DT case, why
don't you make a patch about how you could support Guenter's use case on
the x86.

His use case is not uncommon, believe it or not, and x86 would benefit from
something this flexible.

>> 
>> Guenter
> 
> Sebastian

Regards

-- Pantelis