Created attachment 136486 [details]
DP link training errors in dmesg with drm.debug=0x1e
I've just booted 4.15-rc6 and I am getting a black external screen (Thinkpad L460 with Ultra Dock and external DP monitor). Stable Kernels (4.14 and older) work just fine.
The dmesg is flooded with link training errors, so I was unable to capture a full system log through SSH. The attached dmesg lines are the last link training messages with drm.debug=0x1e. Thousands of these messages appear every second.
The messages appear right when modesetting kicks in, before Wayland is starting.
This is a major issue, as this is a regression which cause DP displays to fail.
- Thinkpad L460 with Ultra Dock (contains a DP MST hub)
- External DP monitor connected to Ultra Dock
- Arch Linux
- Kernel 4.15-rc6
- Intel Core i5-6200U
The issue is about DP-3 (DP2-1 in X11). eDP1 is working.
Created attachment 136515 [details]
Full kernel debug log (with DMC 1.27)
I managed to get a full debug log, which should be more helpful.
Meanwhile I have also applied https://patchwork.freedesktop.org/patch/187559/ (the log is with new DMC 1.27), but it does not change anything. But in case a log without that patch is required (DMC 1.26) let me know.
Hello Direx, is it possible for you to bisect to find the culprit commit?? Thank you.
Sorry, I am neither a kernel developer nor a git expert, just an enthusiast end user. I've tried fiddling with git, but after all the rebasing in drm-intel I have difficulties bisecting.
All I can say is that 069d40f5834ad26a58f269225a7e13af17019062 is a good commit and 5ea2355a100a3c6304901d058aee06d3a6be69bc is a bad commit.
Author: Imre Deak <email@example.com>
Date: Tue Oct 3 12:51:59 2017 +0300
drm/i915/glk: Fix DMC/DC state idleness calculation
Author: Dhinakaran Pandiyan <firstname.lastname@example.org>
Date: Tue Oct 3 17:22:11 2017 +0300
drm/i915/mst: Use MST sideband message transactions for dpms control
This has been fixed today by:
Author: Lucas De Marchi <email@example.com>
Date: Tue Jan 2 12:18:37 2018 -0800
drm/i915: Apply Display WA #1183 on skl, kbl, and cfl
Maybe you want to add a test for this, so I am leaving the bug open.
Thanks for the follow-up, closing.