linux-kernel - Re: [PATCH/RFC 02/12] dt-bindings: display: renesas: lvds: Document renesas,swap-data

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Message-ID: <20190802074428.GB5008@pendragon.ideasonboard.com>
Date:   Fri, 2 Aug 2019 10:44:28 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Fabrizio Castro <fabrizio.castro@...renesas.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Simon Horman <horms@...ge.net.au>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>
Subject: Re: [PATCH/RFC 02/12] dt-bindings: display: renesas: lvds: Document
 renesas,swap-data

Hi Fabrizio,

Thank you for the patch.

On Fri, Aug 02, 2019 at 08:33:59AM +0100, Fabrizio Castro wrote:
> R-Car D3, R-Car E3, and RZ/G2E support dual-link mode.
> In such a mode, the first LVDS encoder emits even data, and the
> second LVDS encoder emits odd data. This patch documents property
> renesas,swap-data, used to swap even and odd data around.
> 
> Signed-off-by: Fabrizio Castro <fabrizio.castro@...renesas.com>
> ---
>  Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt b/Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt
> index dece79e..8980179 100644
> --- a/Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt
> +++ b/Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt
> @@ -52,6 +52,11 @@ Optional properties:
>    mandatory for the first LVDS encoder on R-Car D3, R-Car E3, and RZ/G2E SoCs,
>    and shall point to the second encoder to be used as a companion in dual-link
>    mode. It shall not be set for any other LVDS encoder.
> +- renesas,swap-data : when in dual-link mode, the first LVDS encoder normally
> +  emits even data, and the second LVDS encoder emits odd data. When property
> +  renesas,swap-data is specified, the data emitted by the two encoders will be
> +  swapped around. This property can only be used in conjunction with property
> +  renesas,companion.

>From an LVDS encoder point of view this is more a configuration option
than a description of the hardware. Wouldn't it be better for the LVDS
sink to report which of the odd or even pixels it expects on each of its
endpoints ? The LVDS encoder driver could then query that at runtime and
configure itself accordingly. Ideally this should be queried through the
drm_bridge_timings structure (or through a similar mean), not through
DT. An LVDS sink that has a fixed mapping of odd/even pixels to
endpoints wouldn't need the information to be specified in DT at all.

>  
>  
>  Example:

-- 
Regards,

Laurent Pinchart