[Bug 111250] i915 external monitor not working in usb-c/thunderbolt dock on X1 gen6

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111250

--- Comment #20 from Stanislav Lisovskiy <stanislav.lisovskiy at intel.com> ---
(In reply to tmai from comment #19)
> First of all, thanks for the patch and all the explaining. I am learning a
> few things here. :-)
> 
> I attached 3 new dmesg files. All were created with a fresh drm-tip kernel +
> patch.
> 
> A brief description of the results:
> 
> 1. Test with noname-dock booted to console: The Monitor (via hdmi cable) was
> connected at a 1024xsomething resolution. Besides the low resolution
> everything seemed to work fine. Afterwards I rebooted to gui (kde). Same
> result, monitor was connected, but with a low resolution. I could not change
> the resolution via the kde settings menu.
> 
> 2. Test with lenovo-dock booted to console: No change here. Still no
> connection to the monitor(s). I tried to monitors with two cables (hdmi and
> dp). The hdmi-monitor works fine when connected directly to the notebook.
> After playing around a little the system eventually crashed. I had to reboot
> with a hard shutdown.
> 
> 3. Test with lenovo-dock booted to gui (kde): Same thing as with the
> console: no monitor worked via the dock. However, I noticed that the hdmi
> monitor connected to the laptop directly still showed a screen, when I
> connected the other monitor as via dp at the dock. In that scenario the
> laptop screen itself went dark, but still showed the mouse cursor.

In 2) from dmesg I see constantly repeating pattern:

[  204.218230] [drm:intel_get_hpd_pins.isra.10 [i915]] hotplug event received,
stat 0x00200000, dig 0x10101011, pins 0x00000020, long 0x00000000
[  204.218245] [drm:intel_hpd_irq_handler [i915]] digital hpd port B - short
[  204.224610] [drm:intel_dp_set_signal_levels [i915]] Using signal levels
07000000
[  204.224628] [drm:intel_dp_set_signal_levels [i915]] Using vswing level 2
[  204.224644] [drm:intel_dp_set_signal_levels [i915]] Using pre-emphasis level
0
[  204.242876] [drm:intel_dp_set_signal_levels [i915]] Using signal levels
07000000
[  204.242892] [drm:intel_dp_set_signal_levels [i915]] Using vswing level 2
[  204.242908] [drm:intel_dp_set_signal_levels [i915]] Using pre-emphasis level
0
[  204.261150] [drm:intel_dp_dump_link_status [i915]] ln0_1:0x0 ln2_3:0x0
align:0x80 sink:0x0 adj_req0_1:0x22 adj_req2_3:0x22
[  204.261166] [drm:intel_dp_start_link_train [i915]] Clock recovery check
failed, cannot continue channel equalization
[  204.261813] [drm:intel_dp_start_link_train [i915]] [CONNECTOR:92:DP-1] Link
Training failed at link rate = 540000, lane count = 4

That obviously explains why it didn't work at least for 2) However in 1) and 3)
there is no such thing, which is a bit strange as in 3) you have same hardware
except you into gui.

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