[Bug 101602] New: [KBL] MST monitors not detected

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101602

            Bug ID: 101602
           Summary: [KBL] MST monitors not detected
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: nutello at sweetness.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 132257
  --> https://bugs.freedesktop.org/attachment.cgi?id=132257&action=edit
dmesg with drm.debug=0xe

I have a new Dell XPS 13 9360. According to drm logs: platform=KABYLAKE gen=9
pciid=0x5926 rev=0x06. I updated from Ubuntu 16.04 to 17.04 and installed Linux
4.12-rc7 (from today).

I also have two Dell U2715H monitors (2560x1440) set up for DP1.2/MST. They
worked well for the past couple of years with a XPS 13 9343 (Broadwell), using
a mini-DP to DP cable.

I'm trying to switch to the new laptop, but it doesn't seem to recognise the
monitors at all. It never did. I am using a Google USB-C to DP cable. If I
revert the monitors back to DP1.1, the first one is detected, but
daisy-chaining won't work (of course). I also have a Dell dock, but I use it
only as a glorified USB and Ethernet hub. In case you're wondering, I don't use
it for anything more, because its USB audio tends to lock up and the gross,
CPU-draining DisplayLink software/hardware hack is utter garbage (to be kind).

Anyway, what really puzzles me about the Kaby Lake laptop is that this is a
regression from two years ago.

I'm attaching dmesg output with drm.debug=0xe. Please advise. The old laptop
sometimes has terrifying loud POST errors about the built-in LCD screen, so
switching to the new one would be timely. :-)

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