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

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Date:   Tue, 21 Mar 2023 19:58:18 +0530
From:   Jayesh Choudhary <j-choudhary@...com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        <dri-devel@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <andrzej.hajda@...el.com>, <neil.armstrong@...aro.org>,
        <rfoss@...nel.org>, <Laurent.pinchart@...asonboard.com>,
        <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>
Subject: Re: [PATCH 1/2] dt-bindings: drm/bridge: Add no-hpd property



On 21/03/23 18:08, Krzysztof Kozlowski wrote:
> On 21/03/2023 13:02, Jayesh Choudhary wrote:
>>>
>>>> +    type: boolean
>>>> +    description:
>>>> +      Set if the HPD line on the bridge isn't hooked up to anything or is
>>>> +      otherwise unusable.
>>>
>>> It's the property of the panel, not bridge. Unless you want to say that
>>> bridge physically does not have HPD? Does it follow the standard in such
>>> case?
>>
>> MHDP does have hpd. But the mhdp driver should handle the cases when the
> 
> This is about bindings, not driver. Your driver can still handle this as
> it wishes.
> 
>> hpd pin of bridge is not connected to that of the DP-connector. This is
>> to add support for that. (optional property)
> 
> Which is indicated by panel no-hpd, right?

Actually no panel is involved in this. For TI SoC J721S2, the data 
pipeline involves the bridge whose endpoint is directly the DP connector 
with compatible 'dp-connector'. And in the binding dp-connector.yaml, 
there isn't any 'no-hpd' property for this indication.

Does this clarifies the issue? Or did I misinterpret your comment?

> Or you mean now that HPD
> physically cannot go to panel because it is cut on the bridge side? But
> isn't this the same case (from hardware/bindings point, not driver) as
> panel would not have HPD?
Warm Regards,
-Jayesh