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From: Alexandru Ardelean <alex@shruggie.ro>
Date: Wed, 3 Apr 2024 09:16:31 +0300
Message-ID: <CAH3L5QooAXDYAxOdMkPrW1mx04ZgTv_kMU5VSAby9J3Hb_RFOg@mail.gmail.com>
Subject: Re: [PATCH 2/2] dt-bindings: display: bridge: lt8912b: document
 'lontium,pn-swap' property
To: Conor Dooley <conor@kernel.org>
Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, 
	devicetree@vger.kernel.org, adrien.grassein@gmail.com, 
	andrzej.hajda@intel.com, neil.armstrong@linaro.org, rfoss@kernel.org, 
	Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se, jernej.skrabec@gmail.com, 
	airlied@gmail.com, daniel@ffwll.ch, maarten.lankhorst@linux.intel.com, 
	mripard@kernel.org, tzimmermann@suse.de, robh@kernel.org, 
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org, 
	stefan.eichenberger@toradex.com, francesco.dolcini@toradex.com, 
	marius.muresan@mxt.ro, irina.muresan@mxt.ro
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On Tue, Apr 2, 2024 at 9:06=E2=80=AFPM Conor Dooley <conor@kernel.org> wrot=
e:
>
> 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 swap=
ped.
> > 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@shruggie.ro>
> > ---
> >  .../devicetree/bindings/display/bridge/lontium,lt8912b.yaml | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/display/bridge/lontium,l=
t8912b.yaml b/Documentation/devicetree/bindings/display/bridge/lontium,lt89=
12b.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_a=
nd_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
> >