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Subject: Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap_devices to mach-omap2)
From: Koen Kooi <koen@dominion.thruhere.net>
In-Reply-To: <CACxGe6vu8ek7-K-yDDMXyg9x-oKiFt_cSz+Pz-yZf5U5vwe=0g@mail.gmail.com>
Date: Mon, 12 Nov 2012 12:03:23 +0100
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>,
        Rob Herring <robherring2@gmail.com>,
        Deepak Saxena <dsaxena@linaro.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Scott Wood <scottwood@freescale.com>, Tony Lindgren <tony@atomide.com>,
        Russ Dill <Russ.Dill@ti.com>, Felipe Balbi <balbi@ti.com>,
        Benoit Cousson <b-cousson@ti.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Matt Porter <mporter@ti.com>, linux-omap@vger.kernel.org,
        Kevin Hilman <khilman@ti.com>, Paul Walmsley <paul@pwsan.com>,
        devicetree-discuss@lists.ozlabs.org
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To: Grant Likely <grant.likely@secretlab.ca>
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Op 5 nov. 2012, om 21:40 heeft Grant Likely <grant.likely@secretlab.ca> het volgende geschreven:

> Hey folks,
> 
> As promised, here is my early draft to try and capture what device
> tree overlays need to do and how to get there. Comments and
> suggestions greatly appreciated.
> 
> Device Tree Overlay Feature
> 
> Purpose
> =======
> Sometimes it is not convenient to describe an entire system with a
> single FDT. For example, processor modules that are plugged into one or
> more modules (a la the BeagleBone), or systems with an FPGA peripheral
> that is programmed after the system is booted.
> 
> For these cases it is proposed to implement an overlay feature for the
> so that the initial device tree data can be modified by userspace at
> runtime by loading additional overlay FDTs that amend the original data.
> 
> User Stories
> ============
> Note - These are potential use cases, but just because it is listed here
> doesn't mean it is important. I just want to thoroughly think through the
> implications before making design decisions.

I think the beaglebone use cases cover it as well, but it deserves a seperate mention: SOMs. Gumstix is a good example of those, their website has a list of the different expansionboards they sell so we can see if we missed a use case somewhere.
Their expansionboards have an EEPROM to ID them, just like the beagleboard classic/xM expansionboards, but I don't know if all 3rd party vendors honour that standard. I know the Ettus USRP E-100 on my desk has it.

regards,

Koen--
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