linux-kernel - Re: [RESEND PATCH v5 2/3] dt-bindings: display: atmel: optional video-interface of endpoints

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Date:   Fri, 3 Aug 2018 10:51:43 +0200
From:   jacopo mondi <jacopo@...ndi.org>
To:     Peter Rosin <peda@...ntia.se>
Cc:     linux-kernel@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        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>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, Jyri Sarha <jsarha@...com>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>
Subject: Re: [RESEND PATCH v5 2/3] dt-bindings: display: atmel: optional
 video-interface of endpoints

On Fri, Aug 03, 2018 at 10:40:02AM +0200, Peter Rosin wrote:
> On 2018-08-03 10:11, jacopo mondi wrote:
> > Hi Peter!
> >
> > On Fri, Aug 03, 2018 at 09:23:07AM +0200, Peter Rosin 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.
> >>
> >> Acked-by: Boris Brezillon <boris.brezillon@...tlin.com>
> >> Reviewed-by: Rob Herring <robh@...nel.org>
> >> Signed-off-by: Peter Rosin <peda@...ntia.se>
> >> ---
> >>  .../devicetree/bindings/display/atmel/hlcdc-dc.txt | 26 ++++++++++++++++++++++
> >>  1 file changed, 26 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt b/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt
> >> index 82f2acb3d374..9de434a8f523 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>.
> >
> > Is there any value in specifying this, if it has a fixed value to
> > "autodetect"? I understand it's optional, so if nobody else objects,
> > feels free to keep it there.
>
> That's just how media/video-interfaces.txt works.
>
> bus-type 0 means that other properties describe the bus type. In this
> case bus-width is specified, so that means a parallel bus. But bus-width
> has no meaning (or may not have) if bus-type is non-zero. But checking
> that bus-type for zero in the code seemed like overkill to me since the
> driver already knows that it is a parallel bus...
>

Yeah, I felt like pointing that out since you're not cheking for its value,
and that property is only used by v4l2-fwnode to handle some
not-that-used-anymore bus as CCP2 is.

> TL;DR I'd like to keep it.
>

Fine with me then.

> >
> >> + - bus-width: recognized values are <12>, <16>, <18> and <24>, and
> >> +   override any output mode selection heuristic, forcing "rgb444",
> >> +   "rgb565", "rgb666" and "rgb888" respectively.
> >> +
> >>  Example:
> >>
> >>  	hlcdc: hlcdc@...30000 {
> >> @@ -50,3 +58,21 @@ Example:
> >>  			#pwm-cells = <3>;
> >>  		};
> >>  	};
> >> +
> >
> > Two blank lines here.
> >
> >> +
> >> +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 {
> >
> > The node has a unit address specified, you're missing a reg = <0>
> > property (no big deal, it's an example, but the other one has it)
> >
> >> +				hlcdc_panel_output: endpoint@0 {
> >
> > Missing reg here too.
>
> I'll fix those (I think they appeared for the original example after I
> wrote the patch).
>

Ok, then please consider also describing the port@0 node cell sizes too
since it has a child endpoint node.

Cheers
  j

> Cheers,
> Peter
>
> > Minors apart:
> >
> > Reviewed-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> >
> > Thanks
> >    j
> >
> >> +					bus-type = <0>;
> >> +					bus-width = <16>;
> >> +				};
> >> +			};
> >> +		};
> >> +	};
> >> --
> >> 2.11.0
> >>
>

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