Re: [PATCH 0/5] Adjustments to common mode behavior

["Timur Kristóf" <timur.kristof@gmail.com>]

On 9/24/25 19:48, Mario Limonciello wrote:

> 
>> A slightly related question, would you be OK with changing the link 
>> detection code to return dc_connection_none when DDC cannot read an 
>> EDID header on digital signals, similar to how the non-DC code does it?
>>
> 
> I personally think lining up all these nuances that are different 
> between the two is a good idea.e e
> 
> But for that specific question that's probably more of a Harry/Alex Hung 
> question.

@Harry and @Alex, what do you guys think about this?

>>>>
>>>> Two possible cases come to mind:
>>>> 1. When we are unable to read the EDID for some reason
>>>> 2. When the EDID is buggy and/or doesn't contain any modes
>>>> Are these issues real or am I overthinking it?
>>>>
>>>> Thanks & best regards,
>>>> Timur
>>>
>>> Failing to read EDID has happened in the past, but I think with the 
>>> deferred aux message handling that should be cleared up now.
>>
>> I was actually curious about that. I saw that issue while I was 
>> working on something else. How is it deferred now? Can you point me to 
>> the series that fixed it?
>>
> 
> There's more patches than this one, but I believe this was the 💰 patch.
> 
> https://lore.kernel.org/amd-gfx/20250428135514.20775-27-ray.wu@amd.com/
> 

I'm not sure if that deals with the same issue that I'm referring to.

Basically what I notice is that when plugging in a cable, it can happen 
that the HPD pins make contact before the DDC pins, and hence DC fails 
to read the EDID. This can happen often with DVI ports and rarely with 
HDMI (and never happened to me with DP).

The non-DC code has a solution for this to retry in a few seconds.
I wasn't able to find anything for this in DC.
I found some code to set up some HPD filters, but that code is not 
called from anywhere and I was told the HPD filter may not be the right 
solution.

So my question is, what would be the right solution? Can we use a HPD 
filter? Or better to do what the non-DC code does and just retry again 
later?

Thanks,
Timur