linux-kernel - Re: [PATCH v1 3/6] dt-bindings: display: bridge: toshiba,tc358768: add parallel input mode

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Date:   Mon, 3 Apr 2023 23:20:10 +0200
From:   Francesco Dolcini <francesco@...cini.it>
To:     Rob Herring <robh@...nel.org>
Cc:     Francesco Dolcini <francesco@...cini.it>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        dri-devel@...ts.freedesktop.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        devicetree@...r.kernel.org,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/6] dt-bindings: display: bridge: toshiba,tc358768:
 add parallel input mode

On Mon, Apr 03, 2023 at 04:01:17PM -0500, Rob Herring wrote:
> On Fri, Mar 31, 2023 at 11:40:01AM +0200, Francesco Dolcini wrote:
> > On Fri, Mar 31, 2023 at 10:48:15AM +0200, Krzysztof Kozlowski wrote:
> > > On 30/03/2023 11:59, Francesco Dolcini wrote:
> > > > From: Francesco Dolcini <francesco.dolcini@...adex.com>
> > > > 
> > > > Add new toshiba,input-rgb-mode property to describe the actual signal
> > > > connection on the parallel RGB input interface.
> > > > 
> > > > Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
> > > > ---
> > > >  .../bindings/display/bridge/toshiba,tc358768.yaml | 15 +++++++++++++++
> > > >  1 file changed, 15 insertions(+)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/display/bridge/toshiba,tc358768.yaml b/Documentation/devicetree/bindings/display/bridge/toshiba,tc358768.yaml
> > > > index 8f22093b61ae..2638121a2223 100644
> > > > --- a/Documentation/devicetree/bindings/display/bridge/toshiba,tc358768.yaml
> > > > +++ b/Documentation/devicetree/bindings/display/bridge/toshiba,tc358768.yaml
> > > > @@ -42,6 +42,21 @@ properties:
> > > >    clock-names:
> > > >      const: refclk
> > > >  
> > > > +  toshiba,input-rgb-mode:
> > > > +    description: |
> > > > +      Parallel Input (RGB) Mode.
> > > > +
> > > > +      RGB inputs (PD[23:0]) color arrangement as documented in the datasheet
> > > > +      and in the table below.
> > > > +
> > > > +      0 = R[7:0], G[7:0], B[7:0]
> > > 
> > > RGB888?
> > 
> > Or anything else - like a RGB666 - just connecting to GND the unused
> > pins.
> 
> If the bridge is configured for RGB666, then that's fine. If not, the 
> unused pins should be driven with either the MSB of each component. 
> Otherwise, you'd can't fully saturate the colors.

maybe a detail and maybe not really relevant, but this specific bridge
has no know-how on the actual RGB inputs width. While I understand what
you are saying here, in the end this is about the actual hardware design
that can be in any way, including having pins to gnd and have the issue
you just described.

Francesco