Re: [PATCH 6.16.y] Revert "drm/dp: Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS"

[Imre Deak <imre.deak@intel.com>]

On Thu, Sep 04, 2025 at 03:20:23PM +0200, Wolfgang Frisch wrote:
> Hi Imre,
> 
> 
> On 9/2/25 6:13 PM, Imre Deak wrote:
> > This looks like the issue tracked at
> > https://gitlab.freedesktop.org/drm/amd/-/issues/4500
> Thanks! I wasn't aware of that issue being tracked already.
> 
> > The correct solution there is to disable the DPCD probing, which AMD
> > folks are working on atm. Until that, could you give a go to patch [1]
> > on the above ticket equivalent to this solution, applying on v6.17, or
> > the attached patch achieving the same on v6.16.4?
> I can confirm your patch fixes the issue on v6.16.4.
> > Also it would help if you could add a dmesg log on the ticket taken
> > after booting with drm.debug=0x100 and reproducing the problem (vs. two
> > other drm.debug=0x100 logs, one with the above DP_TRAINING_PATTERN_SET
> > -> DP_LANE0_1_STATUS change and another one with DPCD probing disabled
> > as I requested above, taken after booting up and connecting the
> > dock/monitor).
> Done. I attached 3 dmesg logs to the ticket:

Thanks for the testing.

> - GOOD: Linux 6.16.4 with DPCD probing disabled
> - BAD: Linux 6.17.0-rc4

This is expected, as it still does DPCD probing leading to the original
TBT firmware issue tracked on the above ticket.

> - GOOD: Linux 6.17.0-rc4 with the probe address set to DP_LANE0_1_STATUS

Switching the DPCD probing address to DP_LANE0_1_STATUS is not a viable
solution, as it causes an issue for at least one other (eDP) panel. The
probing should be disabled according to the following AMD patch:

https://gitlab.freedesktop.org/-/project/4522/uploads/5205fd4e2bdc396088836bafcac176b6/0004-drm-amd-display-Disable-DPCD-Probe-Quirk.patch

--Imre

> Regards,
> 
> -- 
> Wolfgang Frisch <wolfgang.frisch@suse.com>
> Security Engineer
> OpenPGP fingerprint: A2E6 B7D4 53E9 544F BC13  D26B D9B3 56BD 4D4A 2D15
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