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I use TumbleWeed as my main OS, and also have a separate TumbleWeed partition
to test the updates first. So my main system is still on 5.10.16-1-default,
while the test system is on 5.11.6-1, after trying 5.11.2-1.

There is no graphic card besides the one embedded in the CPU, with the built-in
drivers, which so far has been good enough for me.

On the test system, my 3440x1440 monitor is now seen as 2560x1080 (or sometimes
1024x768 or 1600x900), in the sense that you cannot set a higher resolution.

The reason I'm saying this has to do with the kernel rather than with X, is
what happens at boot: I use "nosplash", to see the boot messages. On the
old/main system, there is some text with a large font for less than 1 second,
and then it enters a text mode with around 90 lines, and then the X graphics
mode of 3440x1440. On the updated system, the first boot goes the same in the
text modes, but at reboots the text mode is really some 77 visible lines (or
sometimes fewer), but it still thinks there are 90, so what happens is the
bottom lines and right columns aren't shown. (Well, the bottom visible line is
truncated, only the top of the characters are seen.) I think these text modes
are configured before X had a chance to do anything, so it looks more like some
"garbage" left in some memory from a previous run that decides the resolution.

It didn't occur to me to try the older kernel (5.10.16-1) when I saw that
things no longer worked as expected with 5.11.6-1, which would have made it
clearer if the issue is with the kernel or not. Now I'm not sure how to go
about installing an older kernel, as I don't see it in YaST.

However, there is a workaround of sorts: Disconnect the DP cable and reconnect
it. Then I can set the resolution to 3440x1440@60. This seems to make the text
mode (e.g. Ctrl+Alt+F1) unavailable, though.


Reproducible: Always

Steps to Reproduce:
1. Start TumbleWeed with "nosplash" on a 3440x1440 monitor (Samsung CF791) and
TW as of 2021.03.21
2. Reboot, once it started

Actual Results:  
1. In text mode during boot, bottom lines are not visible.
2. In graphics mode the resolution is something smaller (usually 2560x1080) and
cannot be made 3440x1440

Expected Results:  
1. All text lines should be visible during boot (except maybe the first boot).
2. It should be possible to set the resolution to 3440x1440@60
3. The resolution should be kept between reboots.