Re: [PATCH 2/2] dt-bindings: display: bridge: lt8912b: document 'lontium,pn-swap' property

[Alexandru Ardelean]

On Tue, Apr 2, 2024 at 9:06 PM Conor Dooley <conor@xxxxxxxxxx> wrote:
>
> On Tue, Apr 02, 2024 at 01:59:25PM +0300, Alexandru Ardelean wrote:
> > On some HW designs, it's easier for the layout if the P/N pins are swapped.
> > The driver currently has a DT property to do that.
>
> "currently", because 1/2 adds it. bindings patches should precede the
> driver patches in the series, so please swap the patches and remove this
> portion of the description.

ack;
i'll invert the order and remove this;

>
> >
> > This change documents the 'lontium,pn-swap' property.
> >
> > Signed-off-by: Alexandru Ardelean <alex@xxxxxxxxxxx>
> > ---
> >  .../devicetree/bindings/display/bridge/lontium,lt8912b.yaml | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/display/bridge/lontium,lt8912b.yaml b/Documentation/devicetree/bindings/display/bridge/lontium,lt8912b.yaml
> > index 2cef252157985..3a804926b288a 100644
> > --- a/Documentation/devicetree/bindings/display/bridge/lontium,lt8912b.yaml
> > +++ b/Documentation/devicetree/bindings/display/bridge/lontium,lt8912b.yaml
> > @@ -24,6 +24,12 @@ properties:
> >      maxItems: 1
> >      description: GPIO connected to active high RESET pin.
> >
> > +  lontium,pn-swap:
> > +    description: Swap the polarities of the P/N pins in software.
> > +      On some HW designs, the layout is simplified if the P/N pins
> > +      are inverted.
>
> Please explain what configuration of a board would cause these to be
> swapped, rather than why someone might want to configure the board this
> way. I've got no idea what this hardware is actually doing, so this is
> being pulled out of a hat, but I'd expect something like "Some boards
> swap the polarity of the P/N pins, use this property to indicate this to
> software".

ack
if it's fine with you, i'll use your suggested description;

for a broader context, we were using a DSI-HDMI converter [1] from
SomLabs on a different (than SomLabs) board;
and we were not seeing anything on the HDMI-connected display;
as I understand it, some DSI-HDMI bridges support P/N auto-inversion;
this one doesn't AFAICT;
on this DSI-HDMI converter [1], we've noticed that the P/N pins were
inverted from the DSI to the chip (vs what we expected to see)
after changing the register value (for the P/N swap), it worked;
our conclusion was that, the design of the converter (board) was done
as-such, because it made the layout easier

[1] https://wiki.somlabs.com/index.php/SL-MIPI-LVDS-HDMI-CNV-11_Datasheet_and_Pinout

>
> > +    type: boolean
>
> The type here should be flag.

ack; i'll change the type

>
> Cheers,
> Conor.
>
> > +
> >    ports:
> >      $ref: /schemas/graph.yaml#/properties/ports
> >
> > --
> > 2.44.0
> >