[Bug 106223] New: UDH 620: Number of DP lane is not consistently probed

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=106223

            Bug ID: 106223
           Summary: UDH 620: Number of DP lane is not consistently probed
           Product: DRI
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: ricardo.ribalda at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 139073
  --> https://bugs.freedesktop.org/attachment.cgi?id=139073&action=edit
Screen detected as HD

Tested on Debian 4.15 and 4.16 (from experimental)

I have a secondary monitor connected via USB-C adapter to HDMI (detected as DP
by xrandr). It can manage resolutions up to 2560x1440.

Most of the time, when the system is booted the resolution is detected
ok, but If I suspend the machine, or replug the screen, or alternate
to the text console, the resolution is "downgraded" to Full HD.

It is very anonying to reconect the cable up to 5 times to get the expected
resolution when this happens. 

I have added the paramter drm.debug=0x06 and I can see that when it is on Full
HD there are only 2 lanes detected instead of 4.

The adapter is brand new (Xiaomi) and the cable should be of good
quality (ethernet capable and tested on other platform).

Attached you will find a trace at Full HD and 1440p

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