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Date: Tue, 17 Jan 2023 14:38:57 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Aradhya Bhatia <a-bhatia1@...com>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com>,
Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.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
On 09/01/2023 18:21, Aradhya Bhatia wrote:
> 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@...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.
>
> 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. :)
I can imagine a panel which you can use with a single LVDS link if the
clock is high enough, or two LVDS links if the clock has to be lower. Is
that a dual-lvds panel? =)
But probably that situation is no different than a panel that can work
with DSI or DPI input.
Still, I'm agree with Angelo in that a new compatible string for dual
link lvds feels a bit odd. That said, it's possible the panel-lvds
bindings might get rather confusing. So I don't have a strong feeling here.
Tomi
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