Arch Linux

FuzzySPb

Member

Registered: 2013-01-21

Posts: 46

[SOLVED] No 4K (UHD, 3840x2180) resolution for external display

Hi,
I have Dell 4K capable display and Acer notebook with i915 and Nvidia graphics and Linux/Windows dual boot.
HDMI is quite limited to 3840x2180 @ 24Hz but it is ok and when I boot to Windows it works fine.
Under Linux I don't have 3840x2180 option by default. Here is `xrandr` output for HDMI:

HDMI-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
   1920x1080     60.00    60.00    50.00    59.94    25.00    24.00    23.98* 
   1920x1080i    60.00    50.00    59.94  
   1600x1200     60.00  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1280x720      60.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x576i      50.00  
   720x480       60.00    59.94  
   720x480i      60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  

There are 1920x1080 at maximum. As experiment I did:

$ cvt 3840 2160 24
$ xrandr --newmode "3840x2160_24.00"  266.75  3840 4056 4456 5072  2160 2163 2168 2192 -hsync +vsync
$ xrandr --addmode HDMI-1 "3840x2160_24.00"

The mode was added successfully and I was able to select and use it after it. But it disappeared after system reboot.

I think this prooves that Linux is able to use 4K resolution successfully but somehow it isn't detected automatically.
Could you give me an advice what to do to make it available without manual manipulations with modes?

$ lspci -k | grep -A 2 -E "(VGA|3D)"
00:02.0 VGA compatible controller: Intel Corporation CometLake-U GT2 [UHD Graphics] (rev 02)
        Subsystem: Acer Incorporated [ALI] Device 1410
        Kernel driver in use: i915
--
06:00.0 3D controller: NVIDIA Corporation GP108M [GeForce MX250] (rev a1)
        Subsystem: Acer Incorporated [ALI] Device 1410
        Kernel driver in use: nvidia
$ xrandr --listmonitors
Monitors: 1
 0: +HDMI-1 1920/597x1080/336+0+0  HDMI-1
$ 

Last edited by FuzzySPb (2021-10-09 13:42:43)

Lone_Wolf

Member

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 11,911

Re: [SOLVED] No 4K (UHD, 3840x2180) resolution for external display

Post xorg log please.
Is the monitor connected to the intel or the nvidia card ?

How is the hdmi cable labeled ?

---

Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.

(A works at time B)  && (time C > time B ) ≠  (A works at time C)

FuzzySPb

Member

Registered: 2013-01-21

Posts: 46

Re: [SOLVED] No 4K (UHD, 3840x2180) resolution for external display

Lone_Wolf, unfortunately I can't answer your questions:
- I know it's important to know which card serves monitor but I don't know right command to check it.
- I use "noname" cable, but I know that it works (as I wrote I checked it with Windows and with manual workaround via 'xrandr' newmode)

With regards to Xorg.log  - I think it isn't needed anymore as I found how to solve the problem.
I created a file /etc/X11/xorg.conf.d/10-monitor.conf with following content (I was guided by xrandr ArchWiki page):

Section "Monitor"
    Identifier "HDMI-1"
    Modeline "3840x2160_24.00"  266.75  3840 4056 4456 5072  2160 2163 2168 2192 -hsync +vsync
    Option "PreferredMode" "3840x2160_24.00"
EndSection

I took Modeline from cvt output that I posted above.

Last edited by FuzzySPb (2021-10-09 13:46:42)