Re: [PATCH v3 1/2] dt-bindings: media: renesas,vin: Add binding for V4M

["Niklas Söderlund" <niklas.soderlund+renesas@ragnatech.se>]

Hi Conor,

On 2024-06-21 09:21:24 +0200, Geert Uytterhoeven wrote:
> Hi Niklas,
> 
> On Thu, Jun 20, 2024 at 7:22 PM Niklas Söderlund
> <niklas.soderlund+renesas@ragnatech.se> wrote:
> > On 2024-06-20 17:27:00 +0100, Conor Dooley wrote:
> > > > +      - items:
> > > > +          - enum:
> > > >                - renesas,vin-r8a779g0 # R-Car V4H
> > > > +              - renesas,vin-r8a779h0 # R-Car V4M
> > > > +          - const: renesas,rcar-gen4-vin # Generic R-Car Gen4
> > > >
> > > > If so I can see that working as I could still fix any issues that come
> > > > from differences between V4H and V4M if needed. If so do you think it
> > > > best to add this in two different patches? One to add the
> > > > renesas,rcar-gen4-vin fallback (which will also need DTS updates to fix
> > > > warnings from exciting users of V4H not listing the gen4 fallback) and
> > > > one to add V4M?
> > >
> > >
> > > I would just do:
> > > diff --git a/Documentation/devicetree/bindings/media/renesas,vin.yaml b/Documentation/devicetree/bindings/media/renesas,vin.yaml
> > > index 5539d0f8e74d..22bbad42fc03 100644
> > > --- a/Documentation/devicetree/bindings/media/renesas,vin.yaml
> > > +++ b/Documentation/devicetree/bindings/media/renesas,vin.yaml
> > > @@ -54,6 +54,9 @@ properties:
> > >                - renesas,vin-r8a77995 # R-Car D3
> > >                - renesas,vin-r8a779a0 # R-Car V3U
> > >                - renesas,vin-r8a779g0 # R-Car V4H
> > > +      - items:
> > > +          - const: renesas,vin-r8a779h0 # R-Car V4L2
> > > +          - const: renesas,vin-r8a779g0 # R-Car V4H
> >
> > @Geert: What do you think about this? This would be a first use-case for
> > compatibles crossing SoC DTS files that I know of. I'm a bit uneasy
> > going down this road.
> 
> Me too ;-)
> 
> > Would this not also effect the existing users of renesas,vin-r8a779g0
> > which would now need something similar to what you propose below with a
> > list of SoC compatibles and a fallback.
> >
> > >
> > >    reg:
> > >      maxItems: 1
> > >
> > > Which requires no driver or dts changes. That could become:
> > >       - items:
> > >           - enum:
> > >               - renesas,vin-r8a779h0 # R-Car V4L2
> > >               - renesas,vin-r8a779i0 # R-Car R4P17
> > >           - const: renesas,vin-r8a779g0 # R-Car V4H
> >
> > FWIW, on Gen2 where fallback es where useful compared to Gen3 we did
> > this with "renesas,rcar-gen2-vin".
> 
> We do know there are differences (albeit probably small) among the R-Car
> Gen4 VIN implementations, so I am reluctant to add a family-specific
> compatible value.  Typically we only use a family-specific compatible
> value if the IP cores are known (or better, assumed ;-) to be identical.
> 
> And sometimes our assumptions turn out to be wrong...
> See slides 25-33 (last two for the numbers) of my talk at ER2019
> https://embedded-recipes.org/2019/talks/herd-your-socs-become-a-matchmaker/

Do Geert's slides help to explain the R-Car perspective on why a 
family-specific fallback compatible might not be desirable, and why the 
SoC specific one is proposed? 

-- 
Kind Regards,
Niklas Söderlund