Question about screen resolution in plasma 5 using x11 and a 4 K monitor arrangement.
1i5t5.duncan at cox.net
Mon Mar 14 11:49:29 GMT 2022
Patrick Nagel posted on Sun, 13 Mar 2022 09:09:44 +0000 (UTC) as
> Hi Stakanov,
> 13.03.2022 09:56:02 Stakanov <stakanov at disroot.org>:
>> It came to my mind that maybe the Plasma desktop cannot be resolved
>> over the proposed 2160x1140.
>> Could you tell me if plasma has a resolution limit and maybe cannot
>> fully resolve 4K? This would help me very much.
> I'm running Plasma 5.22 (and have been running other 5.x versions) on a
> 4k monitor without issue. Also using X11 on Kubuntu with Nvidia GPU
I've been running plasma from live-git-master for years, on xorg until a
bit over a year ago, on wayland since (I took advantage of covid down time
to do the big switch, originally having to hack-patch a lot of bug
workarounds, now most are fixed).
Plasma definitely does 4K, even dual 4K, as I've been using dual 4K big-
screen TVs as monitors now for several years, since well before the switch
to wayland so I know it works on both xorg and wayland.
Tho with dual monitors plasmashell will place a different wallpaper and
activity on each, not one spread across both (tho the virtual desktop
combines both activities/monitors).
It's a Radeon graphics system too, tho an older one from about a decade
ago, polaris-11 chip family, AMD Radeon RX 460 with 4 gig graphics card
RAM, 16 gig system RAM. Running Gentoo ~amd64 (the ~ indicates testing,
not stale^h^hble), currently mesa-22.0.0, kernel 5.17.0-rc8 (released
yesterday/Sunday). I actually no longer have xorg installed so the only X
I have is xwayland running on wayland.
The card has three outputs, HDMI, DP, DVI (unused), with a DP-HDMI cable
on the DP so both TVs are connected via HDMI ports.
At least back on xorg, tho, I did initially have problems getting
3840x2160 at full 60 Hz, it'd only give me 30 Hz, until I found a setting
I had wrong on the TVs. IIRC it wasn't set to UHD or something, so
wouldn't give me 60 Hz at native resolution, only 30 Hz, or lower
resolution. Of course I had that worked out long before I switched to
wayland, so I don't know what plasma-wayland would have done with it.
So check that. Perhaps your monitor will do UHD aka 3840x2160 at 60, but you
need to switch something to get it to do that (apparently it's a common
option on 4K TVs, no idea on non-TV monitors), and for some reason without
that available to it, xorg or kde is preferring the lower resolution but
higher frequency to the lower frequency 3840x2160 at 30 that I got.
Tho I may have gotten that because on xorg I did have the xorg
configuration (files in xorg.conf.d) set to 3840x2160 for both outputs. I
guess it might have tried the lower resolution higher frequency if I
didn't have it specifically configured for the native resolutions.
Meanwhile, I have the kernel configured for framebuffer use instead of the
legacy vgabuf, with the builtin kernel commandline (CONFIG_CMDLINE)
including: video=HDMI-A-1:3840x2160 video=DVI-D-1:3840x2160 , and I get
exactly that for text mode, tho it's duped to both outputs as I've not
figured out how to do different on each for text mode, if it's even
possible at all. (I don't use a graphical login, booting to a textmode
login prompt from which I login, and if I want to go graphical I start
kde, now wayland mode formerly xorg mode, from the CLI. I have weston
installed and configured so I can run it from the CLI instead, if the
after all live-git plasma session won't run.)
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.)
If it's listed, you can try running xrandr --help and figure out the
xrandr syntax needed to try switching to it with xrandr instead of using
kscreen or whatever. If xrandr will switch to it you have confirmation
that it's a kde/plasma problem; if xrandr tries to switch but the result
is garbled or there are other problems, maybe kde is detecting those and
refused it as a result.
** Do be aware, however, with multiple monitors at least, I often have (on
wayland now, but back on xorg too) problems with plasmashell switching
activities and panels to the wrong monitors if I do resolution switches.
I can usually recover, but sometimes it's just easier to quit back to the
CLI and start a new kde session. So save all your work and be prepared to
exit your kde session and start a new one if necessary, before you start
messing with resolution switches. **
Other than that, I'll second the suggestion to try booting another distro,
from a USB stick or something. But plasma can definitely handle at least
side-by-side 4K, totaling 7680x2160, on both xorg and wayland, because
I've been doing that for years.
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
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