linux-kernel - Re: [PATCH v2 1/2] dt-bindings: drm/bridge: Add no-hpd property

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Date:   Fri, 14 Apr 2023 20:13:58 +0530
From:   Jayesh Choudhary <j-choudhary@...com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     <dri-devel@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <krzysztof.kozlowski@...aro.org>,
        <andrzej.hajda@...el.com>, <neil.armstrong@...aro.org>,
        <rfoss@...nel.org>, <jonas@...boo.se>, <jernej.skrabec@...il.com>,
        <airlied@...il.com>, <daniel@...ll.ch>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <sam@...nborg.org>,
        <jani.nikula@...el.com>, <tzimmermann@...e.de>,
        <javierm@...hat.com>, <ville.syrjala@...ux.intel.com>,
        <r-ravikumar@...com>, <lyude@...hat.com>,
        <alexander.deucher@....com>, <sjakhade@...ence.com>,
        <yamonkar@...ence.com>, <a-bhatia1@...com>,
        <tomi.valkeinen@...asonboard.com>
Subject: Re: [PATCH v2 1/2] dt-bindings: drm/bridge: Add no-hpd property



On 06/04/23 07:10, Laurent Pinchart wrote:
> Hi Jayesh,
> 
> Thank you for the patch.
> 
> On Wed, Apr 05, 2023 at 07:54:39PM +0530, Jayesh Choudhary wrote:
>> From: Rahul T R <r-ravikumar@...com>
>>
>> The mhdp bridge can work without its HPD pin hooked up to the connector,
>> but the current bridge driver throws an error when hpd line is not
>> connected to the connector. For such cases, we need an indication for
>> no-hpd, using which we can bypass the hpd detection and instead use the
>> auxiliary channels connected to the DP connector to confirm the
>> connection.
>> So add no-hpd property to the bindings, to disable hpd when not
>> connected or unusable.
>>
>> Signed-off-by: Rahul T R <r-ravikumar@...com>
>> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
>> ---
>>   .../devicetree/bindings/display/bridge/cdns,mhdp8546.yaml   | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/display/bridge/cdns,mhdp8546.yaml b/Documentation/devicetree/bindings/display/bridge/cdns,mhdp8546.yaml
>> index c2b369456e4e..3a6c6d837593 100644
>> --- a/Documentation/devicetree/bindings/display/bridge/cdns,mhdp8546.yaml
>> +++ b/Documentation/devicetree/bindings/display/bridge/cdns,mhdp8546.yaml
>> @@ -57,6 +57,12 @@ properties:
>>     interrupts:
>>       maxItems: 1
>>   
>> +  cdns,no-hpd:
>> +    type: boolean
>> +    description:
>> +      Set if the HPD line on the bridge isn't hooked up to anything or is
>> +      otherwise unusable.
> 
> I'm fine with the non connected part, but concerned with "otherwise
> unusable". It's very vague and could thus be abused. Do you have
> particular use cases in mind for this ? If so, restricting this to those
> use cases, or at least giving examples, would help.

Okay. Will do that in next version.

Thanks.

> 
>> +
>>     ports:
>>       $ref: /schemas/graph.yaml#/properties/ports
>>   
>