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

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Date:   Thu, 23 Mar 2023 17:56:21 +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>,
        <tomi.valkeinen@...asonboard.com>
Subject: Re: [PATCH 1/2] dt-bindings: drm/bridge: Add no-hpd property



On 21/03/23 20:47, Krzysztof Kozlowski wrote:
> 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...
> 

Okay. I will edit the commit message in v2. (after further review of the 
driver changes for this series)

I will mention that 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, using this 
optional property, we can bypass the hpd detection and instead use the 
auxiliary channels connected to the DP connector to confirm the connection.

Thanks,
-Jayesh