[RFC] Interrupt mapping documentation

[Benjamin Herrenschmidt]

> If there's precedence for it, it's fine with me.  I was just curious  
> about why it changed.  Personally, I'd rather see it as "pic",  
> because that's more specific, and it's the actual device name, but  
> it's not keeping me up at night.....

I'll revert the example to "pic". I thing Segher is right, let's leave
some freedom there.

> That also works for me.  I'd rather have to specify more stuff in the  
> tree and have it be crystal clear how it's interpreted and used.  So,  
> is this true for just #address-cells, or does it affect #size-cells  
> as well?

Yes. The OF spec says that #size-cells defaults to 1 when absent but I'd
rather make it mandatory. It's not used for interrupt tree resolving
though thus it's not necessary in interrupt-controller nodes.

> Sounds good.  The dtc should probably throw an error (or at least a  
> warning) on this, so the trees get fixed.  I think I'd prefer to see  
> an error - that will keep this problem from propagating any further.

Yup.

> > In the case of interrupt controllers/nexus, #address-cells is not for
> > addressable sub-nodes though but for defining the format of unit
> > interrupt specifiers for interrupt-childs which aren't necessary sub
> > nodes... confusing heh ?
> 
> Um, yeah :)  I think with a little clarification it will be fine,  
> though.

Yeah, it's a bit complicated and I'm not that good at writing very clear
english :) I'll try to do a second pass on that part of the spec. In
fact, the only case where #address-cells is required in an interrupt
controller node (and that node is a leaf node, not also a bus), is when
an interrupt nexus points to it (that is an interrupt-map). I should
make that clear in the spec. If you don't use interrupt maps, you should
not need that #address-cells in the interrupt-controller.

Ben.