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

[Aradhya Bhatia <a-bhatia1@ti.com>]

Hi Krzysztof,

Thank you for reviewing the patches!

On 03-Jan-23 14:02, Krzysztof Kozlowski wrote:
> On 03/01/2023 07:46, Aradhya Bhatia wrote:
>> 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/#
> 
> Drop trailing /

Okay, will do!

> 
>> +
>> +properties:
>> +  compatible:
>> +    oneOf:
>> +      - items:
>> +          - enum:
>> +              - lincolntech,lcd185-101ct
>> +              - microtips,13-101hieb0hf0-s
>> +          - const: panel-dual-lvds
>> +      - const: panel-dual-lvds
> 
> You cannot have this compatible alone
Okay, will make the change!

> 
>> +
>> +  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]
>> +          - required: [dual-lvds-even-pixels]
>> +
>> +      port@1:
>> +        $ref: /schemas/graph.yaml#/$defs/port-base
>> +        unevaluatedProperties: false
>> +        description: The sink for second set of LVDS pixels.
>> +
>> +        properties:
>> +          dual-lvds-even-pixels:
>> +            type: boolean
>> +
>> +          dual-lvds-odd-pixels:
>> +            type: boolean
>> +
>> +        oneOf:
>> +          - required: [dual-lvds-even-pixels]
>> +          - required: [dual-lvds-odd-pixels]
>> +
>> +    allOf:
>> +      - if:
>> +          properties:
>> +            port@0:
>> +              properties:
>> +                dual-lvds-odd-pixels: true
> 
> That's not correct clause. It has no effect.

The idea behind this is to check the presence of the boolean property.

if (dual-lvds-odd-pixels is present)
then
[..]


I tried implementing this:

	[..]
	  dual-lvds-odd-pixels:
	    - const: true
	[..]

But this is throwing an error. I am confused what else could be done.
Can you please suggest what might be a more accurate check here?

> 
>> +              required:
>> +                - dual-lvds-odd-pixels
>> +        then:
>> +          properties:
>> +            port@1:
>> +              properties:
>> +                dual-lvds-even-pixels: true
>> +                dual-lvds-odd-pixels: false
> 
> Why do you need this? Your oneOf before already solves it.

I agree with your comment here. It makes sense to only have

	dual-lvds-even-pixels: true

and have the oneOf condition take care of the other. But, I just tested
this and it was unable to pick-up this intentionally-added error.

I added 'dual-lvds-odd-pixels' property to both the nodes, and
dt_binding_check passes successfully (which it should have not.)

Instead, if I only keep this,

	dual-lvds-odd-pixels: false

then the dt_binding_check detects the error as it should.

Regardless, I am curious why the first method doesn't work. Will try to
explore more on that.

> 
>> +
>> +      - if:
>> +          properties:
>> +            port@0:
>> +              properties:
>> +                dual-lvds-even-pixels: true
>> +              required:
>> +                - dual-lvds-even-pixels
>> +        then:
>> +          properties:
>> +            port@1:
>> +              properties:
>> +                dual-lvds-odd-pixels: true
>> +                dual-lvds-even-pixels: false
>> +
>> +    required:
>> +      - port@0
>> +      - port@1
>> +
>> +  port: false
>> +
>> +unevaluatedProperties: false
>> +
>> +required:
>> +  - compatible
>> +  - width-mm
>> +  - height-mm
>> +  - data-mapping
>> +  - panel-timing
>> +  - ports
>> +
>> +examples:
>> +  - |+
> 
> Drop +

Okay!

> 
>> +    panel-dual-lvds {
> 
> Just "panel". Node names should be generic.

Alright. Will make the change!

> 
>> +      compatible = "microtips,13-101hieb0hf0-s", "panel-dual-lvds";
>> +
>> +      width-mm = <217>;
>> +      height-mm = <136>;
>> +
> 
Regards
Aradhya