Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000

[Benjamin Martin <benjamin@bmg7.com>]

Hi Tj,


This is the GPU >> https://www.techpowerup.com/gpu-specs/t400.c3808

The 3 monitors are :

Dell U2722DE connected to DP 1

Dell U2722D connected to DP 2 and 3

All monitors are connected with mini display port to normal display port 
cables.

Both monitors models have DP pass-through, meaning each monitor also has 
a display port output. (This only works if the GPU supports that, I do 
not know if my GPU (the Nvidia T400) supports DP pass-through.

Best Regards,

Benjamin

On 7/26/25 09:49, Tj wrote:
> I've had some time to come back to this now there's a lot of to-and-fro with more data. Looking at
>
> https://bugs.debian.org/cgi-bin/bugreport.cgi?att=2;bug=1088522;filename=Debian6.15boot.log;msg=63
>
> that contains three boots:
>
> 1. 2 monitors
> 2. 3 monitors
> 3. 2 monitors
>
> I think the cause is pretty obvious. Nouveau needs to ask the GPU how many outputs it has and query each for monitor capabilities. That is done over i2c. It looks to me as if an incorrect i2c auxiliary channel is being used.
>
> I further suspect commit 752a281032b2 may give us a lead to what is going on here. Note its commit message specifically calls out crashing GPUs that have off-chip Display Port.
>
> I scanned the bug messages but didn't find any detail about how the monitors are connected (also, some adapters use DP internally but expose the output via HDMI).
>
> So let's also get the exact make/model of the GPU adapter.