Dear Maintainer,

For about half a year I had Dell UltraSharp 30" U3014 connected to my HP
15-rb063nw laptop as the primary display in the joint displays setting
and working at its native resolution 2560x1600 (60 Hz, at least I think
so).

Yesterday I made a test of working on the notebook alone by setting it
to single build-in display (without disconnecting the HDMI cable).

When trying to return to the previous setting, I found 2560x1600 is
available at 59.99 HZ (not on the drop down list!)m but when applied,
the Dell monitor goes blank and enters the power save mode.

I now work with the Dell set to 1920x1080 at 60 Hz with a strange
flickering (not the whole screen, rather a polygon is flashing at the
top, and not all the time, usually after a mouse movement).

The monitor is definitely OK, it behaves as expected with MS Windows and
another computer.

I will appreciate very much you help.

Best regards

Janusz

Without any configuration change (at least without any conscious one)
the situation deteriorated:

1. I cannot use the external editor at all.

2. A strange flicker-like effect appears in some circumstances also on
the build-in display.

Janusz

Given some other experiences with amdgpu modesetting
problems, and looking at this bug, I would say:-

1) Please try updating all packages and reboot and
     try again, kernel should be now  4.19.0-16

2) Secondly, enable backports
https://backports.debian.org/Instructions/
     and then:-

apt-get -t buster-backports install linux-image-amd64 linux-headers-amd64


This should get you a 5.10 series kernel.  My strong experience with
amdgpu has been that a whole lot of modesetting, sleep, etc etc.
issues are massively improved in 5.10 kernel series of late,
irrespective of the xserver-xorg version in use.

NB: At boot-time, in normal cases, GRUB menu should allow you
to 'select' which kernel you boot into i.e you should be
able to select between 5.10.0.bpo.?? and 4.19.0-16 kernel.

I note, the backports kernel is lagging behind a little,
hopefully 5.10.0-0.bpo.6 and 5.10.0-0.bpo.7 will come
out soon.

Dear Janusz

linux-image-amd64 linux-headers-amd64 have now come out in version
5.10.0-0.bpo.7 in buster-backports.

Please confirm the issue is solved for you (or not) by using that
kernel as above, so the bug report can be prgressed or closed.

Unfortunately there is no improvement.

Only the console output is displayed on the external monitor.

Actually I stopped using the laptop, during a quick test there was no
flickering, but it appeared usually after some time.

The monitor is OK because Windows uses it with no problem at the native
resolution.

Please note the problem seems specific to a particular model of laptop,
during a quick test with a desktop the problem doesn't occur even with
the default kernel.

Best regards

Janusz