[Bug 111502] Dell XPS15 (HD530 & GeForce 950) external screen via dock/HDMI no text display & gdm freeze

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111502

Imre Deak <imre.deak at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ville.syrjala at linux.intel.c
                   |                            |om

--- Comment #8 from Imre Deak <imre.deak at intel.com> ---
Could you check if your kernel has

commit bb1a71f9c4672fbfcf2158fd57d0c5c0cdae5612
Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
Date:   Wed Aug 28 13:20:59 2019 +0300

    drm/i915: Limit MST to <= 8bpc once again

and if not retry with that patch applied?

In your case the MST modeset fails with >8bpc mode:
[    3.638886] [drm:drm_dp_mst_atomic_check [drm_kms_helper]] [MST
PORT:00000000400f0099] requires 65 vcpi slots
[    3.638888] [drm:drm_dp_mst_atomic_check [drm_kms_helper]] [MST
PORT:00000000400f0099] not enough VCPI slots in mst state 0000000007efd79c
(avail=63)

...

[    3.639117] [drm:intel_plane_destroy [i915]] cpu_transcoder: B, pipe bpp:
36, dithering: 0

The failure shouldn't cause a machine hang, but it's worth trying if the
failure path leads to it somehow. Your case is also only about 1 MST stream,
unlike the case the above commit fixes, so looks like we also calculate the
available bandwidth incorrectly.

Adding Ville for more ideas.

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