Comment 87 for bug 1785912

Looking at dump_pipe_config, I don't see big differences.

setup_hw_state:
[drm:intel_dump_pipe_config [i915]] dp m_n: lanes: 4; gmch_m: 6213395, gmch_n: 8388608, link_m: 517782, link_n: 524288, tu: 64

Only thing in link is:

modeset:
[drm:intel_dump_pipe_config [i915]] dp m_n: lanes: 4; gmch_m: 6213395, gmch_n: 8388608, link_m: 1035565, link_n: 1048576, tu: 64

Doubt that causes it..

But could always try a lower m/n value..

In i915/intel_dp.c:
 bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
        DP_DPCD_QUIRK_CONSTANT_N);

Change to
bool constant_n = true;