[Bug 103369] [CI] igt at kms_* fail - igt-kms-WARNING: connector 76/eDP-1 has no modes

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103369

--- Comment #49 from Imre Deak <imre.deak at intel.com> ---
Looks like the modes on eDP are pruned due to too high mode clock. That in turn
is caused by a previous link training failure:

<7>[ 2153.428268] [drm:intel_dp_dump_link_status [i915]] ln0_1:0x11 ln2_3:0x11
align:0x80 sink:0x0 adj_req0_1:0x77 adj_req2_3:0x77
<7>[ 2153.428303] [drm:intel_dp_start_link_train [i915]] Channel equalization
failed 5 times
<7>[ 2153.428341] [drm:intel_dp_start_link_train [i915]] [CONNECTOR:76:eDP-1]
Link Training failed at link rate = 270000, lane count = 4

which sets the ports maximum link rate to 162000 and afterwards causes failed
modesets:
<7>[ 2153.723132] [drm:drm_mode_debug_printmodeline] Modeline 80:"3200x1800" 60
361310 3200 3248 3280 3316 1800 1802 1807 1816 0x48 0xa
<7>[ 2153.723247] [drm:intel_dp_compute_config [i915]] DP link computation with
max lane count 4 max bw 162000 pixel clock 361310KHz
<7>[ 2153.723355] [drm:intel_atomic_check [i915]] Encoder config failure
<7>[ 2153.723465] [drm:intel_dump_pipe_config [i915]] [CRTC:42:pipe A][failed]

and pruned modes:

<7>[ 2154.575833] [drm:drm_mode_prune_invalid] Not using 3200x1800 mode:
CLOCK_HIGH

One question is why link training fails, but also if we should reset the link
rate limitation sometime afterwards. Currently for eDP it'd only happen during
system resume or reloading the driver, since eDP ignores long HPDs where the
link rate limit is reset atm.

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