[Bug 217545] New: Serious regression on amdgpu (drm_display_helper/drm_dp_atomic_find_time_slots) with two DisplayPort connected via a HP G5 docking station

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=217545

            Bug ID: 217545
           Summary: Serious regression on amdgpu
                    (drm_display_helper/drm_dp_atomic_find_time_slots)
                    with two DisplayPort connected via a HP G5 docking
                    station
           Product: Drivers
           Version: 2.5
    Kernel Version: 6.1
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri@kernel-bugs.osdl.org
          Reporter: bugzilla.kernel.bpeb@manchmal.in-ulm.de
        Regression: Yes

Created attachment 304404
  --> https://bugzilla.kernel.org/attachment.cgi?id=304404&action=edit
lscpi

This was previously mentioned in comment 69 in
https://bugzilla.kernel.org/show_bug.cgi?id=204181 but I reckon it's a
different story.

Hardware:

* Notebook hp mt45 with

    03:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc.
[AMD/ATI] Picasso/Raven 2 [Radeon Vega Series / Radeon Vega Mobile Series]
[1002:15d8] (rev d3)

  Also briefly confirmed with a Thinkpad T495 with

    06:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc.
[AMD/ATI] Picasso/Raven 2 [Radeon Vega Series / Radeon Vega Mobile Series]
[1002:15d8] (rev d2)

* HP G5 USB-C docking station (HSN-IX02)

Problem:

After upgrading from kernel 6.0 to 6.1, the host crashes once a *second*
external display is connected via DisplayPort on that docking station:

    BUG: kernel NULL pointer dereference, address: 0000000000000008
    RIP: 0010:drm_dp_atomic_find_time_slots+0x47/0x250 [drm_display_helper]

(see attachment for full log)

Another way to reproduce this:

* Use the Ubuntu 23.04 installer/test image.
* Boot with displays disconnected.
* Select "Try Ubuntu".
* Connect displays.
* Upon connecting the second display, the system freezes.


Insights found after bisecting:

* This was introduced with commit

    commit a5c2c0d164e96d24f73faffcd3b7bbb607e701a9
    Author: Lyude Paul <lyude@redhat.com>
    Date:   Wed Aug 17 15:38:37 2022 -0400

        drm/display/dp_mst: Add nonblocking helpers for DP MST

* Later this was half-fixed with commit

    commit efa4c4df864ecd969670093524d3e8f69188e5eb
    Author: Harry Wentland <harry.wentland@amd.com>
    Date:   Mon Feb 13 17:36:55 2023 -0500

        drm/amd/display: call remove_stream_from_ctx from res_pool funcs

Now the notebook no longer crashes, however the displays remain dark although
from the operating system's point of view they are connected and should show
some content. This may or may not be a userland problem. (Aside: This commit
should be backported to the 6.1 stable series. It applies and likewise reduces
the problem from "crash" to "dark screens" there.)

This situation still exists with 6.4-rc6 (released last night)

Please advise if there's anything else we can do.

Find attached:

* lscpi
* dmesg (with drm.debug=4)
* kernel.log (the actual crash)

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