Re: [PATCH 2/4] dt-bindings: panel: lvds: Add properties for clock and data polarities

[Maxime Ripard <maxime@cerno.tech>]

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On Fri, Feb 14, 2020 at 05:11:56PM +0100, Sam Ravnborg wrote:
> Hi Maxime.
>
> On Fri, Feb 14, 2020 at 01:24:39PM +0100, Maxime Ripard wrote:
> > Some LVDS encoders can support multiple polarities on the data and
> > clock lanes, and similarly some panels require a given polarity on
> > their inputs. Add a property on the panel to configure the encoder
> > properly.
> >
> > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
>
> Not a fan of this binding...
> In display-timing.txt we have a specification/description of
> the panel-timing node.
>
> The panel-timing node already include information such as:
> - hsync-active:
> - vsync-active:
> - de-active:
> - pixelclk-active:
> - syncclk-active:
>
> But clock-active-low and data-active-low refer to the bus
> more than an individual timing.
> So maybe OK not to have it in a panel-timing node.
> But then it would IMO be better to include
> this in the display-timing node - so we make
> this available and standard for all users of the
> display-timing node.
>
> I will dig up my patchset to make proper bindings for panel-timing and
> display-timing this weeked and resend them.
> Then we can discuss if this goes on top or this is specific for the
> lvds binding.

That makes sense, I'll wait for them to be merged then :)

>
> > ---
> >  Documentation/devicetree/bindings/display/panel/lvds.yaml | 10 ++++++++-
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/display/panel/lvds.yaml b/Documentation/devicetree/bindings/display/panel/lvds.yaml
> > index d0083301acbe..4a1111a1ab38 100644
> > --- a/Documentation/devicetree/bindings/display/panel/lvds.yaml
> > +++ b/Documentation/devicetree/bindings/display/panel/lvds.yaml
> > @@ -90,6 +90,16 @@ properties:
> >        CTL2: Data Enable
> >        CTL3: 0
> >
> > +  clock-active-low:
> > +    type: boolean
> > +    description: >
>
> Should this be "|" and not ">"?
> Did this pass dt_binding_check?

Yes. > means that this is a multi-line string that will drop the \n
between each line, while | will keep it

For a string like this, I believe it makes more sense to let whatever
is using to handle the wrapping, but I don't really have a strong
opinion :)

>
> > +      If set, reverse the clock polarity on the clock lane.
> This text could be a bit more specific. If this is set then
> what?
> And it seems strange that a clock is active low.
> For a clock we often talk about raising or falling edge.
>
> > +
> > +  data-active-low:
> > +    type: boolean
> > +    description: >
> Same comment with ">"
>
> > +      If set, reverse the bit polarity on all data lanes.
> Same comment about a more explicit description.

I'll try to come up with something better. Thanks!
Maxime

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