[Bug 199797] New: Low resolution on monitor reconnect with amdgpu and Dell P2715Q

[Bug 199797] New: Low resolution on monitor reconnect with amdgpu and Dell P2715Q

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=199797

            Bug ID: 199797
           Summary: Low resolution on monitor reconnect with amdgpu and
                    Dell P2715Q
           Product: Drivers
           Version: 2.5
    Kernel Version: 4.16.10
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri@kernel-bugs.osdl.org
          Reporter: joh@pseudoberries.com
        Regression: No

Created attachment 276131
  --> https://bugzilla.kernel.org/attachment.cgi?id=276131&action=edit
Verbose drm log (echo 0xff > /sys/module/drm/parameters/debug)

When I unplug and plug in my Dell P2715Q monitor, the resolution is wrong. I
get 800x600@75Hz instead of the native resolution (3840x2160@60Hz). Sometimes
I'm able to switch to the native resolution with xrandr, other times xrandr
reports that it cannot find the mode. In that case it helps to turn the monitor
off and on, after which the mode is available to xrandr (EDID issue?).

dmesg reports the following error:
[drm:dm_restore_drm_connector_state [amdgpu]] *ERROR* Restoring old state
failed with -22

I use a kvm switch with the monitor, so the monitor is reconnected quite often.
I've eliminated the kvm switch as the source of the problem by plugging the
monitor directly into the GPU (an AMD RX560), and replugging the displayport
cable.

I've tried dumping the EDID to /lib/firmware and booting with
drm.edid_firmware=edid/DELL-P2715Q.bin, but this doesn't seem to help.

Verbose drm log attached.

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