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

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Date:   Tue, 21 Mar 2023 16:17:28 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jayesh Choudhary <j-choudhary@...com>,
        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 21/03/2023 15:28, Jayesh Choudhary wrote:
> 
> 
> 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?

Yes, then you only need to narrow which hardware does not have HPD
hooked up. Or at least clarify that it is not about driver having or not
having HPD control...


Best regards,
Krzysztof