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

David Gibson
2012-11-13T07:23:55Z

On Mon, Nov 12, 2012 at 10:22:07PM -0700, Stephen Warren wrote:
> On 11/12/2012 06:05 PM, David Gibson wrote:
> > On Fri, Nov 09, 2012 at 09:42:37PM +0000, Grant Likely wrote:
> ...
> > 2) graft bundle
> >
> > The base tree has something like this:
> >
> > ...
> > i2c@XXX {
> > ...
> > cape-socket {
> > compatible = "vendor,cape-socket";
> > id = "Socket-A";
> > piece-id = "i2c";
> > ranges = < ... >;
> > };
> > };
> > ...
> > spi@YYY {
> > ...
> > cape-socket {
> > compatible = "vendor,cape-socket";
> > id = "Socket-A";
> > piece-id = "spi";
> > ranges = < ... >;
> > };
> > };
> > ...
> > cape-socket {
> > compatible = "vendor,cape-socket";
> > id = "Socket-A";
> > piece-id = "misc";
> > interrupt-map = < ... >;
> > interrupt-map-mask = < ... >;
> > gpio-map = < ... >;
> > gpio-map-mask = < ... >;
> > };
> >
> > Then instead of grafting a single subtree for the socket, we install a
> > "bundle" of subtrees, one each for each of the pieces within the
> > socket. That bundle could either be an actual set of multiple fdts,
> > or they could be placed into one fdt with a dummy root node, something like:
> >
> > / {
> > plugin-bundle;
> > compatible = "vendor,cape-plugin";
> > version = ...;
> > i2c-piece = {
> > piece-id = "i2c";
> > ...
> > };
> > misc-piece = {
> > piece-id = "misc";
> > ...
> > };
> > };
>
> I do like this approach; it's the kind of thing I proposed at:
>
> > http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg20414.html

Roughly, yes, though a little streamlined from the syntax suggested
there.

> One question though: Perhaps the base board has two instances of the
> same type of connector vendor,cape-socket, allowing 2 independent capes
> to be plugged in. When overlaying/grafting the child board's .dts, we'd
> need some way to specify the socket ID that was being plugged into. Is
> that the intent of the "id" property in your base board example above?

Yes, that's exactly what I had in mind for the "id" property.
Property names and other details entirely negotiable at this stage,
of course.

By the by, I think having multiple interchangable sockets could break
the convention based approach for avoiding collisions between phandles
I suggested, but another mail with some better thoughts on that
shortly to be posted.

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!