[RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap_devices to mach-omap2)

[Tony Lindgren]

Hi,

* Tabi Timur-B04825 <B04825 at freescale.com> [121105 13:42]:
> On Mon, Nov 5, 2012 at 2:40 PM, Grant Likely <grant.likely at 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