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

From	Benjamin Martin <benjamin@bmg7.com>
Newsgroups	linux.debian.bugs.dist, linux.debian.kernel
Subject	Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000
Date	2025-07-26 18:20 +0200
Message-ID	<LcPMR-2TXL-1@gated-at.bofh.it> (permalink)
References	(7 earlier) <LcPtv-2TB1-3@gated-at.bofh.it> <LcPtv-2TB1-5@gated-at.bofh.it> <LcPtv-2TB1-1@gated-at.bofh.it> <JNCBI-c7yp-5@gated-at.bofh.it> <LcPtv-2TB1-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Cross-posted to 2 groups.

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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.

Thread

Bug#1088522: nouveau: Unable to boot with 3 monitors on Nvidia GPU Tj <tj.iam.tj@proton.me> - 2025-04-03 20:00 +0200
  Bug#1088522: nouveau: Unable to boot with 3 monitors on Nvidia GPU Benjamin Martin <benjamin@bmg7.com> - 2025-07-21 18:20 +0200
    Bug#1088522: nouveau: Unable to boot with 3 monitors on Nvidia GPU Benjamin Martin <benjamin@bmg7.com> - 2025-07-25 03:30 +0200
      Bug#1088522: nouveau: Unable to boot with 3 monitors on Nvidia GPU Raymond Burkholder <ray@oneunified.net> - 2025-07-26 06:30 +0200
      Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Tj <tj.iam.tj@proton.me> - 2025-07-26 18:00 +0200
        Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Benjamin Martin <benjamin@bmg7.com> - 2025-07-26 18:20 +0200
          Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Benjamin Martin <benjamin@bmg7.com> - 2025-07-31 01:50 +0200
            Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Benjamin Martin <benjamin@bmg7.com> - 2025-08-06 23:20 +0200
              Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Tj <tj.iam.tj@proton.me> - 2025-08-07 11:10 +0200
                Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Benjamin Martin <benjamin@bmg7.com> - 2025-08-07 14:10 +0200
                Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Tj <tj.iam.tj@proton.me> - 2025-08-07 15:40 +0200
                Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Tj <tj.iam.tj@proton.me> - 2025-08-07 17:20 +0200
                Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Tj <tj.iam.tj@proton.me> - 2025-08-08 09:30 +0200
                Bug#1088522: nouveau 0000:01:00.0: i2c: aux 0004: magic wait 00008000 Tj <tj.iam.tj@proton.me> - 2025-08-09 00:20 +0200

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