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Message-ID: <431ddd82-055b-2526-3d5e-f6563e48d264@ti.com>
Date:   Mon, 9 Jan 2023 21:51:00 +0530
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Subject: Re: [RFC PATCH 3/4] dt-bindings: panel: Introduce dual-link LVDS
 panel
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To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Tomi Valkeinen <tomba@kernel.org>,
        Jyri Sarha <jyri.sarha@iki.fi>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Maxime Ripard <maxime@cerno.tech>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Guo Ren <guoren@kernel.org>
CC:     DRI Development List <dri-devel@lists.freedesktop.org>,
        Devicetree List <devicetree@vger.kernel.org>,
        Linux Kernel List <linux-kernel@vger.kernel.org>,
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        Linux C-SKY Arch List <linux-csky@vger.kernel.org>,
        Nishanth Menon <nm@ti.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Rahul T R <r-ravikumar@ti.com>,
        Devarsh Thakkar <devarsht@ti.com>,
        Jai Luthra <j-luthra@ti.com>,
        Jayesh Choudhary <j-choudhary@ti.com>
References: <20230103064615.5311-1-a-bhatia1@ti.com>
 <20230103064615.5311-4-a-bhatia1@ti.com>
 <09f1ca83-c7d5-a186-6fa6-09cdd7a0b9cc@collabora.com>
From:   Aradhya Bhatia <a-bhatia1@ti.com>
In-Reply-To: <09f1ca83-c7d5-a186-6fa6-09cdd7a0b9cc@collabora.com>
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Hi Angelo,

Thanks for taking a look at the patches!

On 03-Jan-23 17:21, AngeloGioacchino Del Regno wrote:
> 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@ti.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@ti.com>
>> +  - Thierry Reding <thierry.reding@gmail.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.

Yes, while they are both LVDS based panels the extra LVDS sink in these
panels, and the capability to decode and display the 2 sets of signals
are enough hardware differences that warrant for an addition of a new
compatible.

> 
> 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.

Yes, exactly. Even while being non-smart, there are going to be more
quirks in future. And it would be better if they have their own
compatible/binding, and are not getting appended in an ever-growing
if-else ladder. :)


Regards
Aradhya