[Bug 111179] [Regression]Multiple monitors via DP TB dock detection/resolution/layout failure after Skylake->Coffeelake upgrade

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111179

--- Comment #10 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
I think the main issues is that your 4x5.4Gbps DP link doesn't have enough
bandwidth to support two 4k at 60 displays:
[   81.717461] [drm:drm_dp_mst_atomic_check [drm_kms_helper]] [MST
PORT:000000006465ad61] requires 47 vcpi slots
[   81.717472] [drm:drm_dp_mst_atomic_check [drm_kms_helper]] [MST
PORT:00000000fb13674f] requires 47 vcpi slots
[   81.717483] [drm:drm_dp_mst_atomic_check [drm_kms_helper]] [MST
PORT:00000000fb13674f] not enough VCPI slots in mst state 000000006830e28e
(avail=16)
[   81.717516] [drm:drm_atomic_check_only [drm]] atomic driver check for
000000004efe656f failed: -28

There is just no way to make that work. The only explanation I have why the SKL
might have worked is that its TB implementation uses multiple DP links for the
TB dock whereas the CFL uses just one link for whatever reason. The TB hardware
supposedly is different between the two platforms.

Our TB guru suggested that you should perhaps try to upgrade the TB firmware on
the machine and see if that helps.

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