[Bug 111659] Kernel panic when waking up after screens go to dpms sleep

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111659

            Bug ID: 111659
           Summary: Kernel panic when waking up after screens go to dpms
                    sleep
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: not set
         Component: DRM/Radeon
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: brad at fnarfbargle.com

Created attachment 145332
  --> https://bugs.freedesktop.org/attachment.cgi?id=145332&action=edit
Multiple instances of the Panic

iMac late 2011 with 2 Thunderbolt displays.

Kernel 5.2 finally got DP routing working to allow both TB displays to work,
however I'm now getting lockups which appear to be triggered in  
radeon_dp_needs_link_train.

I'm capturing these over netconsole as it leaves the machine paralysed.

Attachment faults.txt has 4 separate instances of the fault from 4 different
boots.

This machine stays on 24/7 and this seems to occur when the displays wake up
after a dpms sleep. Having said that I've also seen the fault when doing
something innocuous like changing the audio volume.

Generally at least 2 of the screens wakeup, so I have displays with a
lockscreen asking for a password and a mouse, but the machine is dead. 

The last example in faults.txt left the machine in a state where I could ssh in
and reboot it. All the others required a hard power cycle.

I'm currently using 5.2.11. Previously I was using 4.17, but I can't roll back
prior to 5.2 without losing the second TB display, and it can take hours or
days to hit so bisection would be difficult.

01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
Blackcomb [Radeon HD 6970M/6990M] (prog-if 00 [VGA controller])
        Subsystem: Apple Inc. Radeon HD 6970M
        Flags: bus master, fast devsel, latency 0, IRQ 79
        Memory at 90000000 (64-bit, prefetchable) [size=256M]
        Memory at a8800000 (64-bit, non-prefetchable) [size=128K]
        I/O ports at 2000 [size=256]
        Expansion ROM at a8820000 [disabled] [size=128K]
        Capabilities: [50] Power Management version 3
        Capabilities: [58] Express Legacy Endpoint, MSI 00
        Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
        Capabilities: [100] Vendor Specific Information: ID=0001 Rev=1 Len=010
<?>
        Capabilities: [150] Advanced Error Reporting
        Kernel driver in use: radeon
        Kernel modules: radeon

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