linux-kernel - Re: [PATCH v4 1/2] dt-bindings: drm/bridge: ti-tmds181: Add TI TMDS181 and SN65DP159 bindings

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Message-ID: <dc073509-57d9-4b57-a53f-cd285bff8eae@topic.nl>
Date: Tue, 2 Sep 2025 16:52:48 +0200
From: Mike Looijmans <mike.looijmans@...ic.nl>
To: Krzysztof Kozlowski <krzk@...nel.org>
CC: dri-devel@...ts.freedesktop.org, Andrzej Hajda <andrzej.hajda@...el.com>,
 Conor Dooley <conor+dt@...nel.org>, David Airlie <airlied@...il.com>,
 Jernej Skrabec <jernej.skrabec@...il.com>, Jonas Karlman <jonas@...boo.se>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>,
 Neil Armstrong <neil.armstrong@...aro.org>, Rob Herring <robh@...nel.org>,
 Robert Foss <rfoss@...nel.org>, Simona Vetter <simona@...ll.ch>,
 Thomas Zimmermann <tzimmermann@...e.de>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] dt-bindings: drm/bridge: ti-tmds181: Add TI
 TMDS181 and SN65DP159 bindings

On 9/2/25 16:41, Mike Looijmans wrote:
> On 9/2/25 15:46, Krzysztof Kozlowski wrote:
>> On 02/09/2025 10:46, Mike Looijmans wrote:
>>>>> +          endpoint:
>>>>> +            $ref: /schemas/media/video-interfaces.yaml#
>>>>> +            unevaluatedProperties: false
>>>>> +
>>>>> +      port@1:
>>>>> +        $ref: /schemas/graph.yaml#/$defs/port-base
>>>>> +        unevaluatedProperties: false
>>>>> +        description: Video port for HDMI output (panel or bridge)
>>>>> +
>>>>> +        properties:
>>>>> +          endpoint:
>>>>> +            $ref: /schemas/media/video-interfaces.yaml#
>>>>> +            unevaluatedProperties: false
>>>>> +
>>>>> +    required:
>>>>> +      - port@0
>>>>> +      - port@1
>>>>> +
>>>>> +  ti,source-mode:
>>>>> +    type: boolean
>>>>> +    description:
>>>>> +      Force chip to operate in "source" mode. Allows to use
>>>>> +      a TMDS181 chip (which defaults to sink) as cable driver.
>>>>> +
>>>>> +  ti,sink-mode:
>>>> Aren't these two mutually exclusive? Can same device operate in source
>>>> and in sink mode simultaneously?
>>> They're exclusive, yes. Will add that.
>> Then either define constraints per variant in if:then: or maybe better
>> use string enum. Not sure what applies where, so tricky to say which
>> choice is better.
>>
>> Best regards,
>> Krzysztof
>
> Since there's already going to be an "if" block, it simplifies parsing 
> to keep the booleans. My first attempt was this, but that doesn't work 
> as I'd expect. Adding "slew-rate" to the example dts results in an 
> error, so apparently the "if" block doesn't do what I think it would 
> and I haven't figured out yet what the correct syntax must be:
>
> if:
>   properties:
>     compatible:
>       contains:
>         const: ti,sn65dp159
> then:
>   properties:
>     ti,sink-mode:
>       type: boolean
>       description:
>         Force chip to operate in "sink" mode. Allows to use
>         a DP159 chip (defaults to source) for incoming signals.
>     ti,dvi-mode:
>       type: boolean
>       description: Makes the DP159 chip operate in DVI mode.
>     slew-rate:
>       $ref: /schemas/types.yaml#/definitions/uint32
>       minimum: 0
>       maximum: 3
>       default: 3
>       description: Set slew rate, 0 is slowest, 3 is fastest.
> else:
>   properties:
>     ti,source-mode:
>       type: boolean
>       description:
>         Force chip to operate in "source" mode. Allows to use
>         a TMDS181 chip (which defaults to sink) as cable driver.
>
Hmm, apparently one cannot "add" properties in the "if:" block? The 
opposite approach, disallowing properties, works, e.g.:

if:
   properties:
     compatible:
       contains:
         const: ti,sn65dp159
then:
   properties:
     ti,source-mode: false
else:
   properties:
     ti,sink-mode: false
     ti,dvi-mode: false
     slew-rate: false


This produces the wanted behavior, though it looks counter-intuitive to me.


-- 
Mike Looijmans