Re: [PATCH v5 1/2] dt-bindings: display: bridge: lvds-codec: Document pixel data sampling edge select

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Marek Vasut <marex@denx.de>
Cc: dri-devel@lists.freedesktop.org, Rob Herring <robh+dt@kernel.org>,
	Sam Ravnborg <sam@ravnborg.org>,
	devicetree@vger.kernel.org
Subject: Re: [PATCH v5 1/2] dt-bindings: display: bridge: lvds-codec: Document pixel data sampling edge select
Date: Tue, 19 Oct 2021 09:49:57 +0300	[thread overview]
Message-ID: <YW5qlXPyy6ZOHS6N@pendragon.ideasonboard.com> (raw)
In-Reply-To: <4f235f45-5c03-eaeb-69ac-3d801a1dd58c@denx.de>

Hi Marek,

On Tue, Oct 19, 2021 at 12:18:11AM +0200, Marek Vasut wrote:
> On 10/18/21 9:57 PM, Laurent Pinchart wrote:
> 
> Hi,
> 
> >>>> diff --git a/Documentation/devicetree/bindings/display/bridge/lvds-codec.yaml b/Documentation/devicetree/bindings/display/bridge/lvds-codec.yaml
> >>>> index 1faae3e323a4..708de84ac138 100644
> >>>> --- a/Documentation/devicetree/bindings/display/bridge/lvds-codec.yaml
> >>>> +++ b/Documentation/devicetree/bindings/display/bridge/lvds-codec.yaml
> >>>> @@ -79,6 +79,14 @@ properties:
> >>>>          - port@0
> >>>>          - port@1
> >>>>    
> >>>> +  pclk-sample:
> >>>> +    description:
> >>>> +      Data sampling on rising or falling edge.
> >>>> +    enum:
> >>>> +      - 0  # Falling edge
> >>>> +      - 1  # Rising edge
> >>>> +    default: 0
> >>>> +
> >>>
> >>> Shouldn't this be moved to the endpoint, the same way data-mapping is
> >>> defined as an endpoint property ?
> >>
> >> The strapping is a chip property, not port property, so no.
> > 
> > For this particular chip that's true. I'm still not convinced overall.
> > For some cases it could be a per-port property
> 
> Can you be more specific about "some cases" ?

I'm thinking about bridges that could have multiple parallel inputs.

> > , and moving it there for
> > lvds-codec too could allow implementing helpers to parse DT properties,
> > without much drawback for this particular use case as far as I can see.
> > It's hard to predict the future with certainty of course, so I won't
> > insist.
> 
> The DT bindings and the OS drivers are separate thing, we really 
> shouldn't start bending DT bindings so that they would fit nicely with a 
> specific OS driver model.

DT bindings are not holy beings that live in a mythical heaven way above
the mere mortal drivers, they would be useless without implementations.
It's not about bending them, which I regularly push against during
review, but about structuring them in a way that facilitates
implementations when all other things are equal.

As I said, despite wondering whether or not it would be better to move
the property to the endpoint (and that was a genuine open question), I
won't insist in this case.

-- 
Regards,

Laurent Pinchart