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 16:01:17 -0500
From:   Rob Herring <robh@...nel.org>
To:     Francesco Dolcini <francesco@...cini.it>
Cc:     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 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.

> > > +      1 = R[1:0], G[1:0], B[1:0], R[7:2], G[7:2], B[7:2]
> > > +      2 = 8’b0, R[4:0], G[5:0], B[4:0]
> > 
> > Isn't this RGB565?
> > 
> > Don't we have already properties like this? e.g. colorspace?
> 
> It's not really the colorspace this property.
> 
> tc358768 is a parallel RGB to DSI bridge, it has 24 bit parallel input
> line.
> 
> The way this lines are connected is configurable with this parameter, if you
> look at mode 0 and 1 they all allow to have a RGB888 or a RGB666 or a
> RGB565 mapping. This just configure some internal mux, it's not strictly
> about the RGB mode.

This is the same as other cases. There's a need for describing the 
interface. It keeps coming up and I keep saying to go create something 
common.

Rob