linux-kernel - Re: [PATCH 3/5] dt-bindings: display: simple-bridge: Document DPI color encoder

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Message-ID: <b6320f0b-8605-455f-b834-57a8bdaf3f91@nxp.com>
Date: Thu, 6 Mar 2025 13:49:05 +0800
From: Liu Ying <victor.liu@....com>
To: Maxime Ripard <mripard@...nel.org>
Cc: dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, andrzej.hajda@...el.com, neil.armstrong@...aro.org,
 rfoss@...nel.org, Laurent.pinchart@...asonboard.com, jonas@...boo.se,
 jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
 tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch
Subject: Re: [PATCH 3/5] dt-bindings: display: simple-bridge: Document DPI
 color encoder

On 03/04/2025, Maxime Ripard wrote:
> On Tue, Mar 04, 2025 at 06:15:28PM +0800, Liu Ying wrote:
>> A DPI color encoder, as a simple display bridge, converts input DPI color
>> coding to output DPI color coding, like Adafruit Kippah DPI hat[1] which
>> converts input 18-bit pixel data to 24-bit pixel data(with 2 low padding
>> bits in every color component though). Document the DPI color encoder.
>>
>> [1] https://learn.adafruit.com/adafruit-dpi-display-kippah-ttl-tft/downloads
>>
>> Signed-off-by: Liu Ying <victor.liu@....com>
> 
> So it's just a bunch of signals that aren't wired / set to the ground? I
> assume to free a few GPIOs?

Yes. Freed pins could work as GPIOs or other functions.

> 
> I guess that makes sense.
> 
>> ---
>>  .../display/bridge/simple-bridge.yaml         | 89 ++++++++++++++++++-
>>  1 file changed, 87 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/display/bridge/simple-bridge.yaml b/Documentation/devicetree/bindings/display/bridge/simple-bridge.yaml
>> index 43cf4df9811a..c1747c033040 100644
>> --- a/Documentation/devicetree/bindings/display/bridge/simple-bridge.yaml
>> +++ b/Documentation/devicetree/bindings/display/bridge/simple-bridge.yaml
>> @@ -27,6 +27,7 @@ properties:
>>            - const: adi,adv7123
>>        - enum:
>>            - adi,adv7123
>> +          - dpi-color-encoder
> 
> I don't think we can claim that there's a generic DPI color encoder.
> Maybe we can add the prefix dumb or transparent?

TBH, I don't have a best compatible string and open to suggestions.
"dpi-color-encoder" came up to my mind just because the MIPI DPI standard
documentation mentions *color coding* and this bridge changes the coding,
hence *encoder*.

If folks think "dumb-dpi-color-encoder" or "transparent-dpi-color-encoder"
are good enough, I'd use it.  Just let me know which one to use.

> 
>>            - dumb-vga-dac
>>            - ti,opa362
>>            - ti,ths8134
>> @@ -37,13 +38,31 @@ properties:
>>  
>>      properties:
>>        port@0:
>> -        $ref: /schemas/graph.yaml#/properties/port
>> +        $ref: /schemas/graph.yaml#/$defs/port-base
>> +        unevaluatedProperties: false
>>          description: The bridge input
>>  
>> +        properties:
>> +          endpoint:
>> +            $ref: /schemas/media/video-interfaces.yaml#
>> +            unevaluatedProperties: false
>> +
>> +            properties:
>> +              dpi-color-coding: true
>> +
>>        port@1:
>> -        $ref: /schemas/graph.yaml#/properties/port
>> +        $ref: /schemas/graph.yaml#/$defs/port-base
>> +        unevaluatedProperties: false
>>          description: The bridge output
>>  
>> +        properties:
>> +          endpoint:
>> +            $ref: /schemas/media/video-interfaces.yaml#
>> +            unevaluatedProperties: false
>> +
>> +            properties:
>> +              dpi-color-coding: true
>> +
>>      required:
>>        - port@0
>>        - port@1
>> @@ -61,6 +80,44 @@ required:
>>  
>>  additionalProperties: false
>>  
>> +allOf:
>> +  - $ref: /schemas/display/dpi-color-coding.yaml#
>> +  - if:
>> +      properties:
>> +        compatible:
>> +          contains:
>> +            const: dpi-color-encoder
>> +    then:
>> +      properties:
>> +        ports:
>> +          properties:
>> +            port@0:
>> +              properties:
>> +                endpoint:
>> +                  required:
>> +                    - dpi-color-coding
>> +
>> +            port@1:
>> +              properties:
>> +                endpoint:
>> +                  required:
>> +                    - dpi-color-coding
>> +    else:
>> +      properties:
>> +        ports:
>> +          properties:
>> +            port@0:
>> +              properties:
>> +                endpoint:
>> +                  properties:
>> +                    dpi-color-coding: false
>> +
>> +            port@1:
>> +              properties:
>> +                endpoint:
>> +                  properties:
>> +                    dpi-color-coding: false
>> +
> 
> Also it complicates the binding enough to warrant for another binding for
> that specific "component".

Do you suggest to write a separate/new DT binding for this bridge?

> 
>>  examples:
>>    - |
>>      bridge {
>> @@ -88,4 +145,32 @@ examples:
>>          };
>>      };
>>  
>> +  - |
>> +    bridge {
>> +        compatible = "dpi-color-enoder";
> 
> You have a typo in the compatible.

Hmm, good catch!  I did upgrade dtschema to version 2025.2 with pip3 and
didn't see any warnings/errors reported by dt_binding_check, weird...

> 
> Maxime

-- 
Regards,
Liu Ying