Re: [PATCH] media: dt-bindings: media: renesas,csi2: Update data-lanes property

[Jacopo Mondi]

Hi Niklas,

On Mon, Jan 17, 2022 at 10:23:28AM +0100, Niklas Söderlund wrote:
> Hello Jacopo,
>
> On 2022-01-17 09:11:10 +0100, Jacopo Mondi wrote:
> > Hello Prabhakar,
> >
> > On Thu, Jan 13, 2022 at 10:32:14AM +0000, Lad Prabhakar wrote:
> > > CSI-2 (CSI4LNK0) on R-Car and RZ/G2 supports 4-lane mode which is already
> > > handled by rcar-csi2.c driver. This patch updates the data-lanes property
> > > to describe the same.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> > > ---
> > >  .../devicetree/bindings/media/renesas,csi2.yaml          | 9 ++++++++-
> > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/Documentation/devicetree/bindings/media/renesas,csi2.yaml b/Documentation/devicetree/bindings/media/renesas,csi2.yaml
> > > index e6a036721082..064a0a4c5737 100644
> > > --- a/Documentation/devicetree/bindings/media/renesas,csi2.yaml
> > > +++ b/Documentation/devicetree/bindings/media/renesas,csi2.yaml
> > > @@ -67,7 +67,14 @@ properties:
> > >                  maxItems: 1
> > >
> > >                data-lanes:
> > > -                maxItems: 1
> > > +                items:
> > > +                  minItems: 1
> > > +                  maxItems: 4
> > > +                  items:
> > > +                    - const: 1
> > > +                    - const: 2
> > > +                    - const: 3
> > > +                    - const: 4
> >
> > Seeing "maxItems: 1" there confuses me too, as the property is an
> > array of data-lanes, but I'm afraid your change does not what you
> > intend as it would allow you to specify the number of data lanes as an
> > integer rather than as an array.
> >
> > I think it would probably be correct to set
> >
> >                 data-lanes: true
> >
> > (maybe maxItems: 1 is correct already)
> >
> > And restrict the number of valid combinations in the board DTS file
> > with a construct like:
> >
> >     data-lanes:
> >       oneOf:
> >         - items:
> >             - const: 1
> >             - const: 2
> >             - const: 3
> >             - const: 4
> >         - items:
> >             - const: 1
> >             - const: 2
>
> I don't think this is correct, what if data lanes 2 and 3 are used?
>

These were examples that allow you to accept <1 2> and <1 2 3 4> as
valid properties. If other combinations are accepted they can be
specified there, in your example, <2 3> with

             - items:
               - const: 2
               - const: 3

As lane re-reordering is quite unusual as a feature (afaik) there are
usually just an handful of supported combinations for 1, 2 and 4 data
lanes setups.

If full lane re-ordering is supported then it's enough to set
data-lanes: true and accepts all combinations.

Also, the reason why imho the property should go in the board DTS and
not in the SoC .dtsi is that not all the available data lanes of the
IP-core might be routed out on a specific board.

That's at least my understanding which I would be glad to be disproved
as specifying the valid combinations in each board dts is rather
un-convenient.

Thanks
   j

> >
> > Thanks
> >    j
> >
> > >
> > >              required:
> > >                - clock-lanes
> > > --
> > > 2.17.1
> > >
>
> --
> Kind Regards,
> Niklas Söderlund