Re: [PATCH v4 1/5] dt-bindings: arm: renesas: Document Renesas RZ/G2UL SMARC EVK

[Rob Herring <robh@kernel.org>]

On Tue, Apr 05, 2022 at 02:05:31PM +0200, Krzysztof Kozlowski wrote:
> On 05/04/2022 13:47, Biju Das wrote:
> >> Subject: Re: [PATCH v4 1/5] dt-bindings: arm: renesas: Document Renesas
> >> RZ/G2UL SMARC EVK
> >>
> 
> (...)
> 
> >>>
> >>> And what to do when adding more DT overlays for expansion boards?
> >>> This would become unmanageable soon.
> >>
> >> There are two topics here:
> >> 1. Whether we should follow DT spec. If no, why Renesas is special and for
> >> other cases we follow DT spec? "Unmanageable" is not the answer here,
> >> because other platforms will have the same problem.
> >>
> >> 2. If the answer for above is yes, we follow DT spec, then the question is
> >> how to deal with overlays. In current code - I don't know. Long term,
> >> maybe we need a way to append to existing compatible (to extend it)?
> >> Some expansion boards do not need to change top level compatible, because
> >> they only add constrained features (like Arduino shields with some
> >> regulator). You just add it to DT and presence of new compatible, e.g. of
> >> regulator, is enough. You do not need to change the top level compatible.
> >>
> > 
> > Does the rules for compatible values (most to least descriptive) 
> > also apply to the root node?
> 
> I don't see any exception in DT spec (page 26), so my answer is yes, the
> root node has same meaning of "compatible" as other nodes.

At the end of the day, what matters is can we identify what h/w we are 
running on from the value of 'compatible'. Either way I think the answer 
is yes.

The modern mixture of SoC, baseboard, SoM, expansion cards, etc. doesn't 
map perfectly to compatible's definition. If someone wants to define 
something, then that would be good. However, there's already existing 
practice to take into account.

Rob