[Bug 93578] Intel HD 520 failed to train DP when connected with a external monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93578

--- Comment #3 from John McCorquodale <mcq at astranis.com> ---
Same error here, black screen.  It's a Dell UP2414Q which is a 2-tile DP1.2 MTS
device, i7-6700K.  The UP2414Q is known to be finicky about sinking; this is an
A01 rev of that display, which has fewer problems in that regard than the
highly 
dubious A00 rev (i.e. I don't think we can immediately blame the display). 
Works okay (at least once) in non-MTS DP1.1 mode as a single 3840x2160 30Hz
device.  Happy to be somebody's debug minion; feel free to contact me directly.

---xrandr---

P1-8 connected 1920x2160+0+0 (normal left inverted right x axis y axis) 527mm x
296mm
   1920x2160     59.99*+
DP1-9 connected 1920x2160+0+0 (normal left inverted right x axis y axis) 527mm
x 296mm
   1920x2160     59.99*+
   1920x1200     59.88  
   1920x1080     60.00  
   ...

---dmesg---

[  163.467351] [drm:intel_dp_link_training_channel_equalization [i915]] *ERROR*
failed to train DP, aborting
[  163.606349] [drm:intel_dp_link_training_channel_equalization [i915]] *ERROR*
failed to train DP, aborting
[  163.719993] [drm:intel_dp_link_training_channel_equalization [i915]] *ERROR*
failed to train DP, aborting
[  163.784642] [drm:intel_pipe_config_compare [i915]] *ERROR* mismatch in
ddi_pl
l_sel (expected 0x00000000, found 0x00000001)
[  163.784647] [drm:intel_pipe_config_compare [i915]] *ERROR* mismatch in
shared
_dpll (expected -1, found 0)
[  163.784651] [drm:intel_pipe_config_compare [i915]] *ERROR* mismatch in
dpll_h
w_state.ctrl1 (expected 0x00000000, found 0x00000003)
[  163.784654] [drm:intel_pipe_config_compare [i915]] *ERROR* mismatch in
base.a
djusted_mode.crtc_clock (expected 277250, found 138624)
[  163.784658] [drm:intel_pipe_config_compare [i915]] *ERROR* mismatch in
port_c
lock (expected 540000, found 270000)
...
[several dump_stack]
...
[  167.475902] [drm:intel_dp_link_training_channel_equalization [i915]] *ERROR*

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