[Bug 110782] [drm/i915] Displayport connected screen reports Signal Error after update to 5.1 kernel

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110782

--- Comment #14 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
This is another case where something totally crazy is going on with the M/N
values:

[    6.179040] [drm:intel_dump_pipe_config [i915]] dp m_n: lanes: 4; gmch_m:
1703936, gmch_n: 8388608, link_m: 283989, link_n: 1048576, tu: 14
[    6.179501] [drm:intel_dump_pipe_config [i915]] adjusted mode:
[    6.179549] [drm:drm_mode_debug_printmodeline [drm]] Modeline "": 60 154000
1920 1968 2000 2080 1200 1203 1209 1235 0x0 0x9
[    6.179654] [drm:intel_dump_pipe_config [i915]] crtc timings: 154000 1920
1968 2000 2080 1200 1203 1209 1235, type: 0x0 flags: 0x9
[    6.179755] [drm:intel_dump_pipe_config [i915]] port clock: 540000, pipe src
size: 1920x1200, pixel rate 154000

Based on all those other parameters the m/n values should be like they are in
the good log:
dmesg_good_lts_4.19.46-1.txt:[    7.986521] [drm:intel_dump_pipe_config [i915]]
dp m_n: lanes: 4; gmch_m: 1794230, gmch_n: 8388608, link_m: 299038, link_n:
1048576, tu: 14

but the values used in the bad log are the values for the previous 1680x1050
modeset. So far I can't see any way that could happen unless we somehow skipped
the encoder .compute_config() entirely.

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