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

Koen Kooi
2012-11-12T11:03:32Z

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