[Bug 109006] Hotplugging DP1.2 monitor(s) causes machine to hang waiting for page flip

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109006

            Bug ID: 109006
           Summary: Hotplugging DP1.2 monitor(s) causes machine to hang
                    waiting for page flip
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: hime at is.fucking.moe

Created attachment 142774
  --> https://bugs.freedesktop.org/attachment.cgi?id=142774&action=edit
dmesg: DRM call stack

Greetings,

I am using kernel 4.19.8, I have two 4K panels which have DP1.2 inputs as well
as an AMD RX560 GPU[1]. I am experiencing an issue where my machine softlocks
when they are disconnected & subsequently reconnected. If the monitors are
power-cycled ,or the DP cable is hotplugged, my kernel log slowly accumulates
messages like "*ERROR* [PLANE:36:plane-0] flip_done timed out" meanwhile my
graphical environment hangs, waiting for the pageflip which never successfully
happens. One of my monitors also happens be HDMI2.0 capable, and when connected
via HDMI that monitor *does not* lock up the machine in this way, so I believe
this issue to be DisplayPort specific.

Attached is a dmesg from a recent session exhibiting such a softlock, the
relevant portions are near the end. All my softlocks have `RIP:
0010:prepare_flip_isr+0x5f/0x70 [amdgpu]` in common. I will note that the
driver does seem to at least partially initialize the monitors upon
reconnection, as they do not display "no signal" nor enter sleep mode.


[1]: Advanced Micro Devices, Inc. [AMD/ATI] Baffin [Radeon RX 550 640SP / RX
560/560X] [1002:67ff] (rev cf)

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