linux-kernel - Re: [PATCH v4 4/4] arm64: dts: renesas: r8a779a0: Provide default DSI data-lanes

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Date:   Fri, 26 Nov 2021 15:08:27 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Cc:     linux-renesas-soc@...r.kernel.org,
        Geert Uytterhoeven <geert@...der.be>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 4/4] arm64: dts: renesas: r8a779a0: Provide default
 DSI data-lanes

Hi Kieran,

Thank you for the patch.

On Fri, Nov 26, 2021 at 09:54:45AM +0000, Kieran Bingham wrote:
> The data-lanes is a mandatory property for the endpoints.
> Provide a default when not connected that represents the maximum
> lanes supported by the device.
> 
> A connected device should override the data-lanes if it uses a lower
> number of lanes.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> ---
> 
> This patch is split from 2/4 to keep it's change for distinct review.
> The data-lanes is marked as a mandatory property in the DSI bindings
> (which are out of tree, most recent posting at [0])
> 
> [0] https://lore.kernel.org/all/YQGFP%2FcFoSksPyn+@pendragon.ideasonboard.com/
> 
> The data-lanes property is marked as mandatory, which means it needs to
> be provided even when supplying the port templates which get overridden
> later. Is this expected behaviour?
> 
> Does this have sufficient meaning? Or will it always have to be
> specified by any node overriding anyway...?

Isn't the remote-endpoint also mandatory ?

Given that there's no real good default value for data-lanes that is
significantly more likely than others, I'd prefer dropping the endpoints
from r8a779a0.dtsi and adding them in board files.

>  arch/arm64/boot/dts/renesas/r8a779a0.dtsi | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/renesas/r8a779a0.dtsi b/arch/arm64/boot/dts/renesas/r8a779a0.dtsi
> index fdad8bc4a069..7322c4628e2b 100644
> --- a/arch/arm64/boot/dts/renesas/r8a779a0.dtsi
> +++ b/arch/arm64/boot/dts/renesas/r8a779a0.dtsi
> @@ -2661,6 +2661,7 @@ dsi0_in: endpoint {
>  				port@1 {
>  					reg = <1>;
>  					dsi0_out: endpoint {
> +						data-lanes = <1 2 3 4>;
>  					};
>  				};
>  			};
> @@ -2691,7 +2692,9 @@ dsi1_in: endpoint {
>  
>  				port@1 {
>  					reg = <1>;
> +
>  					dsi1_out: endpoint {
> +						data-lanes = <1 2 3 4>;
>  					};
>  				};
>  			};

-- 
Regards,

Laurent Pinchart