Question about screen resolution in plasma 5 using x11 and a 4 K monitor arrangement.

[Duncan]

Stakanov posted on Mon, 14 Mar 2022 16:26:02 +0100 as excerpted:

> In data lunedì 14 marzo 2022 12:49:29 CET, Duncan ha scritto:
>> Another suggestion:  Try running xrandr (without options should be
>> fine) in a konsole window, and see if it lists 3840x2160 there.  If you
>> see the option there, X should be able to do it and it's probably a
>> kde-plasma thing.  If the resolution isn't listed there, X doesn't
>> think it's possible either, and you'll need to figure out how to get X
>> to see it first.  (There's several different ways to get and then feed
>> X the necessary modeline info; I always used a modeline generator,
>> there's some on the web as well as X utilities available, and setup the
>> xorg.conf config with it.)

> Infact, Xrandr gives:
> xrandr Screen 0: minimum 320 x 200, current 4944 x 1440, maximum 16384 x
> 16384 DisplayPort-0 connected 1920x1080+0+180 (normal left inverted
> right x axis y axis) 509mm x 286mm
>    1920x1080     60.00*+  50.00    59.94
>    1600x1200     60.00
[snip lower resolutions]
> DisplayPort-1 disconnected (normal left inverted right x axis y axis)
> DisplayPort-2 disconnected (normal left inverted right x axis y axis)
> DisplayPort-3 connected primary 2560x1440+2384+0 (normal left inverted
> right x axis y axis) 698mm x 393mm
>    2560x1440     59.95 +  74.97*
>    1920x1200     59.88
[snip lower resolutions]
> 
> So it thinks I cannot do it. But the specs say I can. That is strange.
> I will have to write Lenovo if this monitor was produced with charge
> that cannot do the resolution?

OK, so X isn't seeing the 3840x2160 as possible, at 60 or even the lower 
end 30 Hz.  So you gotta get X to see it, somehow.

Next step, can you find and post your xorg log?  Look in ~/.local/share/
xorg/ file Xorg.0.log or similar, or if X is running as root, in /var/
log/.

That will normally have (among other data about the graphics card, the 
driver for it, input devices and their drivers and settings, etc) a bunch 
of lines for what the monitor says it can do (could be the problem) and 
what X translates that to in its modeline style config (builtin if you've 
not added any modelines manually).

Of particular interest is the EDID clained-supported resolutions from the 
monitor, along with the reported probed modelines.  I happen to have an 
old xorg log still around from back in October (must have been the last 
time I ran xorg).  Here's what mine looks like from that (... indicates 
snips):

...
[    29.256] (II) AMDGPU(0): EDID for output HDMI-A-0
...
[    29.257] (II) AMDGPU(0): First detailed timing is preferred mode
...
[    29.257] (II) AMDGPU(0): Supported established timings:
[snipped the low-res standard legacy timings...]
...
[    29.257] (II) AMDGPU(0): Supported standard timings:
[snipped the medium-res standard legacy timings...]
...
[    29.257] (II) AMDGPU(0): Supported detailed timing:
[    29.257] (II) AMDGPU(0): clock: 594.0 MHz   Image Size:  ...
[    29.257] (II) AMDGPU(0): h_active: 3840  h_sync: 4016  ...
[    29.257] (II) AMDGPU(0): v_active: 2160  v_sync: 2168  ...

*THAT* is actually the first detailed timing mentioned as the preferred/
native mode earlier.  Note the h_active 3840, v_active 2160.

...
[    29.257] (II) AMDGPU(0): Ranges: V min: 24 V max: 75 Hz, H min: 15 H 
max: 135 kHz, PixClock max 605 MHz

*THAT* line has the numbers you'll need if you end up having to manually 
add a modeline.

...
[    29.258] (II) AMDGPU(0): Printing probed modes for output HDMI-A-0
[    29.258] (II) AMDGPU(0): Modeline "3840x2160"x60.0  594.00  3840 4016 
4104 4400  2160 2168 2178 2250 +hsync +vsync (135.0 kHz UeP)
[    29.258] (II) AMDGPU(0): Modeline "4096x2160"x60.0  594.00  4096 4184 
4272 4400  2160 2168 2178 2250 +hsync +vsync (135.0 kHz e)

*THAT* is then the first two of many modelines, X's translation of the 
above EDID to in this case builtin settings that X can actually use.  As 
you will note, the second one is actually 4096x2160 at 60Hz.  That's a 
somewhat wider movie standard, I think, one that both X and the monitor 
can display tho it's above native and slightly aspect-ratio-distorted.

...

But other lines may provide useful debugging info, so I'd suggest posting 
the whole thing, after looking it over to ensure it's not got anything 
sensitive/private in it, of course.  Grabbing the log shortly after 
starting a new session should yield the shortest file for posting, but 
still have all the useful info.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman