[Bug 112136] DP MST with WD15 Dock leads to inconsistent port number

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=112136

Lakshmi <lakshminarayana.vudum at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO
         Whiteboard|                            |Triaged
                 CC|                            |stanislav.lisovskiy at intel.c
                   |                            |om
      i915 platform|                            |CFL
      i915 features|                            |display/DP MST

--- Comment #3 from Lakshmi <lakshminarayana.vudum at intel.com> ---
(In reply to p.pawit from comment #0)
> Created attachment 145815 [details]
> dmesg with "drm.debug=0x1e log_buf_len=1M"
> 
> I am using a Dell Latitude 5491 with the WD15 dockr over USB type-C. The
> Dock is a DP MST Dock which 3 ports: HDMI, mDP and VGA. I am using HDMI and
> mDP. The displays work correctly, however, when I unplug and replug the
> displays, they get new names leading them to reset to the default display
> configuration until I also configure displays with that name.
> 
> Tested to be broken on 5.3.7 as well as 5.4-rc4.
> 
> Attached dmesg and xrandr.
> 
> 1) Booted up while connected to Dock. Displays show up as DP-2-1 (DP-4 in
> the kernel) and DP-5. DP-6 also shows up but is disconnected (this is
> probably the VGA work). The output of xrandr is in xrandr_before_verbose.txt
> 2) Detached dock from system. (See "XXXXXXXXXXXXXX unplug" in dmesg)
> 3) Replug dock to system. (See "XXXXXXXXXXXXXX replug" in demsg)
> 4) DP-2-1 and DP-5 show as disconnected. Monitors show as DP-6 and DP-7
> instead. DP-8 also shows up disconnected.
> 5) End of log (See "XXXXXXXXXXXXXX done" in dmesg)
> 
> Expected behavior: Two monitors show up as DP-2-1 and DP-2-2 and remain that
> way consistently.
> 
> The first time I unplug/replug after boot, this happens without fail.
> However, the later times sometimes the display port name changes sometimes
> it doesn't.
> 
> Linux Distribution: Mint 19.2

Can you please verify the issue with drmtip
(https://cgit.freedesktop.org/drm-tip) with kernel parameters drm.debug=0x1e
log_buf_len=4M. If the problem persists attach the full dmesg from boot.

Also, cc'ing Stan.

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