linux-kernel - Re: [PATCH v2 2/6] dt-bindings: display: atmel: optional video-interface of endpoints

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Date:   Wed, 18 Apr 2018 10:29:00 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Sean Paul <seanpaul@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/6] dt-bindings: display: atmel: optional
 video-interface of endpoints

On Wed, 18 Apr 2018 09:31:53 +0200
Peter Rosin <peda@...ntia.se> wrote:

> On 2018-04-18 09:16, Boris Brezillon wrote:
> > Hi Peter,
> > 
> > On Tue, 17 Apr 2018 15:10:48 +0200
> > Peter Rosin <peda@...ntia.se> wrote:
> >   
> >> With bus-type/bus-width properties in the endpoint nodes, the video-
> >> interface of the connection can be specified for cases where the
> >> heuristic fails to select the correct output mode. This can happen
> >> e.g. if not all RGB pins are routed on the PCB; the driver has no
> >> way of knowing this, and needs to be told explicitly.
> >>
> >> This is critical for the devices that have the "conflicting output
> >> formats" issue (SAM9N12, SAM9X5, SAMA5D3), since the most significant
> >> RGB bits move around depending on the selected output mode. For
> >> devices that do not have the "conflicting output formats" issue
> >> (SAMA5D2, SAMA5D4), this is completely irrelevant.
> >>
> >> Signed-off-by: Peter Rosin <peda@...ntia.se>
> >> ---
> >>  Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt | 8 ++++++++
> >>  1 file changed, 8 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt b/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt
> >> index 82f2acb3d374..244b48869eb4 100644
> >> --- a/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt
> >> +++ b/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt
> >> @@ -15,6 +15,14 @@ Required children nodes:
> >>   to external devices using the OF graph reprensentation (see ../graph.txt).
> >>   At least one port node is required.
> >>  
> >> +Optional properties in grandchild nodes:
> >> + Any endpoint grandchild node may specify a desired video interface
> >> + according to ../../media/video-interfaces.txt, specifically
> >> + - bus-type: must be <0>.
> >> + - bus-width: recognized values are <12>, <16>, <18> and <24>, and
> >> +   override any output mode selection hueristic, forcing "rgb444",  
> 
> heuristic, I'll fix that for v3, so please review as if it wasn't there...
> 
> >> +   "rgb565", "rgb666" and "rgb888" respectively.
> >> +  
> > 
> > Can you add an example or update the existing one to show how this
> > should be defined?  
> 
> For v3, I'll extend the binding with this after the preexisting example:
> 
> ------------------8<-----------------
> Example 2: With a video interface override to force rgb565, as above
> but with these changes/additions:
> 
> &hlcdc {
> 	hlcdc-display-controller {
> 		pinctrl-names = "default";
> 		pinctrl-0 = <&pinctrl_lcd_base &pinctrl_lcd_rgb565>;
> 
> 		port@0 {
> 			hlcdc_panel_output: endpoint@0 {
> 				bus-type = <0>;
> 				bus-width = <16>;
> 			};
> 		};
> 	};
> };
> ------------------8<-----------------
> 
> Is that a good plan, or should I perhaps duplicate the whole example?

Looks good to me, no need to add a new example.

Thanks,

Boris