From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tony Lindgren <tony@atomide.com>
Subject: Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving
 omap_devices to mach-omap2)
Date: Mon, 5 Nov 2012 15:22:19 -0800
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To: Tabi Timur-B04825 <B04825@freescale.com>
Cc: Grant Likely <grant.likely@secretlab.ca>, Pantelis Antoniou <panto@antoniou-consulting.com>, Rob Herring <robherring2@gmail.com>, Deepak Saxena <dsaxena@linaro.org>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Wood Scott-B07421 <B07421@freescale.com>, Kevin Hilman <khilman@ti.com>, Matt Porter <mporter@ti.com>, Koen Kooi <koen@dominion.thruhere.net>, linux-kernel <linux-kernel@vger.kernel.org>, Felipe Balbi <balbi@ti.com>, Russ Dill <Russ.Dill@ti.com>, "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>, "devicetree-discuss@lists.ozlabs.org" <devicetree-discuss@lists.ozlabs.org>
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Hi,

* Tabi Timur-B04825 <B04825@freescale.com> [121105 13:42]:
> On Mon, Nov 5, 2012 at 2:40 PM, Grant Likely <grant.likely@secretlab.ca> wrote:
> 
> > Jane is building custom BeagleBone expansion boards called 'capes'. She
> > can boot the system with a stock BeagleBoard device tree, but additional
> > data is needed before a cape can be used. She could replace the FDT file
> > used by U-Boot with one that contains the extra data, but she uses the
> > same Linux system image regardless of the cape, and it is inconvenient
> > to have to select a different device tree at boot time depending on the
> > cape.
> 
> What's wrong with having the boot loader detect the presence of the
> Cape and update the device tree accordingly?  We do this all the time
> in U-Boot.  Doing stuff like reading EEPROMs and testing for the
> presence of hardware is easier in U-Boot than in Linux.
> 
> For configurations that can be determined by the boot loader, I'm not
> sure overlays are practical.

I guess the beaglebone capes could be stackable and hotpluggable if
handled carefully enough.

Regards,

Tony