linux-kernel - Re: [RFC PATCH 3/4] dt-bindings: panel: Introduce dual-link LVDS panel

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Message-ID: <09f1ca83-c7d5-a186-6fa6-09cdd7a0b9cc@collabora.com>
Date:   Tue, 3 Jan 2023 12:51:45 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Aradhya Bhatia <a-bhatia1@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Tomi Valkeinen <tomba@...nel.org>,
        Jyri Sarha <jyri.sarha@....fi>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Maxime Ripard <maxime@...no.tech>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Guo Ren <guoren@...nel.org>
Cc:     DRI Development List <dri-devel@...ts.freedesktop.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Linux RISC-V List <linux-riscv@...ts.infradead.org>,
        Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
        Linux Mediatek List <linux-mediatek@...ts.infradead.org>,
        Linux C-SKY Arch List <linux-csky@...r.kernel.org>,
        Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rahul T R <r-ravikumar@...com>,
        Devarsh Thakkar <devarsht@...com>,
        Jai Luthra <j-luthra@...com>,
        Jayesh Choudhary <j-choudhary@...com>
Subject: Re: [RFC PATCH 3/4] dt-bindings: panel: Introduce dual-link LVDS
 panel

Il 03/01/23 07:46, Aradhya Bhatia ha scritto:
> Dual-link LVDS interfaces have 2 links, with even pixels traveling on
> one link, and odd pixels on the other. These panels are also generic in
> nature, with no documented constraints, much like their single-link
> counterparts, "panel-lvds".
> 
> Add a new compatible, "panel-dual-lvds", and a dt-binding document for
> these panels.
> 
> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> ---
>   .../display/panel/panel-dual-lvds.yaml        | 157 ++++++++++++++++++
>   MAINTAINERS                                   |   1 +
>   2 files changed, 158 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/display/panel/panel-dual-lvds.yaml
> 
> diff --git a/Documentation/devicetree/bindings/display/panel/panel-dual-lvds.yaml b/Documentation/devicetree/bindings/display/panel/panel-dual-lvds.yaml
> new file mode 100644
> index 000000000000..88a7aa2410be
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/panel/panel-dual-lvds.yaml
> @@ -0,0 +1,157 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/panel/panel-dual-lvds.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Generic Dual-Link LVDS Display Panel
> +
> +maintainers:
> +  - Aradhya Bhatia <a-bhatia1@...com>
> +  - Thierry Reding <thierry.reding@...il.com>
> +
> +description: |
> +  A dual-LVDS interface is a dual-link connection with the even pixels
> +  traveling on one link, and the odd pixels traveling on the other.
> +
> +allOf:
> +  - $ref: panel-common.yaml#
> +  - $ref: /schemas/display/lvds.yaml/#
> +
> +properties:
> +  compatible:
> +    oneOf:
> +      - items:
> +          - enum:
> +              - lincolntech,lcd185-101ct
> +              - microtips,13-101hieb0hf0-s
> +          - const: panel-dual-lvds
> +      - const: panel-dual-lvds
> +
> +  ports:
> +    $ref: /schemas/graph.yaml#/properties/ports
> +
> +    properties:
> +      port@0:
> +        $ref: /schemas/graph.yaml#/$defs/port-base
> +        unevaluatedProperties: false
> +        description: The sink for first set of LVDS pixels.
> +
> +        properties:
> +          dual-lvds-odd-pixels:
> +            type: boolean
> +
> +          dual-lvds-even-pixels:
> +            type: boolean
> +
> +        oneOf:
> +          - required: [dual-lvds-odd-pixels]

One question: why do we need a "panel-dual-lvds" compatible?
A Dual-LVDS panel is a LVDS panel using two ports, hence still a panel-lvds.

If you're doing this to clearly distinguish, for human readability purposes,
single-link vs dual-link panels, I think that this would still be clear even
if we use panel-lvds alone because dual-link panels, as you wrote in this
binding, does *require* two ports, with "dual-lvds-{odd,even}-pixels" properties.

So... the devicetree node would look like this:

panel {
	compatible = "vendor,panel", "panel-lvds";
	....
	ports {
		port@0 {
			.....
			-> dual-lvds-odd-pixels <-
		}

		port@1 {
			.....
			-> dual-lvds-even-pixels <-
		};
	};
};

> +          - required: [dual-lvds-even-pixels]

...Though, if you expect dual-lvds panels to get other quirks in the future,
that's a whole different story and you may actually need the panel-dual-lvds
compatible.

Regards,
Angelo