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

[Wolfgang Frisch]

Hi,

On 8/28/25 7:49 PM, Imre Deak wrote:

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c 
b/drivers/gpu/drm/display/drm_dp_helper.c
-               ret = drm_dp_dpcd_probe(aux, DP_LANE0_1_STATUS);
+               ret = drm_dp_dpcd_probe(aux, DP_TRAINING_PATTERN_SET);

The original commit d34d6feaf4a76833effcec0b148b65946b04cde8 broke my setup, with a monitor connected via Thunderbolt. Linux 6.16.4 temporarily fixed the issue by reverting to DP_LANE0_1_STATUS. My monitor is a Samsung C34J79x connected via Thunderbolt 3.

To be clear:
- working: DP_LANE0_1_STATUS
- not working: DP_TRAINING_PATTERN_SET

With the latter I get:

+thunderbolt 0000:c5:00.6: 2: timeout reading config space 2 from 0x20
+thunderbolt 0000:c5:00.6: 2: timeout reading config space 2 from 0x5
+thunderbolt 0000:c5:00.6: 2: cannot find TB_VSE_CAP_PLUG_EVENTS aborting
 thunderbolt 1-2: new device found, vendor=0x175 device=0x20ab
 thunderbolt 1-2: SAMSUNG ELECTRONICS CO.,LTD C34J79x
 thunderbolt 1-0:2.1: new retimer found, vendor=0x1da0 device=0x8830
+thunderbolt 0000:c5:00.6: 0:6 <-> 2:10 (DP): not active, tearing down
+thunderbolt 0000:c5:00.6: 0:7 <-> 2:10 (DP): not active, tearing down

Best regards

--
Wolfgang Frisch <wolfgang.fri...@suse.com>
Security Engineer
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SUSE Software Solutions Germany GmbH, Frankenstraße 146, 90461 Nürnberg

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