Can't get 4K with Debian on 4B+

#1

I bought a Radxa Rock Pi 4B+ and booted Debian Buster XFCE downloaded from the official mirror. I’m using a monitor which supports at least 2560x1440, but the Rock can’t output a resolution higher than 1920x1080.

Running xrandr, I get:

Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 4096 x 4096
HDMI-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 725mm x 428mm
   1920x1080    60.00*  50.00
   1920x1080i   60.00   50.00
   1280x1024    60.02
   1280x960     60.00
   1280x720     60.00   50.00
   1024x768     60.00
   800x600      60.32   56.25
   720x576      50.00
   720x480      59.94
   2560x1440_60.00  59.96

I added the last line using this tutorial, but trying to set the output to this mode results in:

$ xrandr --output HDMI-1 --mode 2560x1440_60.00
xrandr: Configure crtc 0 failed

How do I enable 4K output from my Rock?

#2

What’s the output of

cat /sys/class/drm/card0-HDMI-A-1/modes
#3

currently Linux stable based kernel (5.10) doesn’t support 4K output. vendor(rockchip) based kernel (4.4) support it.

you can try 4.4 kernel,

sudo apt update
sudo apt install linux-image-4.4.179-12-rockchip-gbf202a62a26c
sudo vi /boot/extlinux/extlinux.conf

then add following line under menu title

default kernel-4.4.179-12-rockchip-gbf202a62a26c

like this

timeout 10
menu title select kernel
default kernel-4.4.179-12-rockchip-gbf202a62a26c

label kernel-5.10.131-2-rockchip-g8802564cbf09
    kernel /vmlinuz-5.10.131-2-rockchip-g8802564cbf09
    initrd /initrd.img-5.10.131-2-rockchip-g8802564cbf09
    devicetreedir /dtbs/5.10.131-2-rockchip-g8802564cbf09
    append earlyprintk console=ttyFIQ0,1500000n8 rw init=/sbin/init rootfstype=ext4 rootwait  root=UUID=4ceb5527-58bb-459e-973b-c8bbb1dcfc2e console=ttyS2,1500000n8

label kernel-4.4.179-12-rockchip-gbf202a62a26c
    kernel /vmlinuz-4.4.179-12-rockchip-gbf202a62a26c
    initrd /initrd.img-4.4.179-12-rockchip-gbf202a62a26c
    devicetreedir /dtbs/4.4.179-12-rockchip-gbf202a62a26c
    append earlyprintk console=ttyFIQ0,1500000n8 rw init=/sbin/init rootfstype=ext4 rootwait  root=UUID=4ceb5527-58bb-459e-973b-c8bbb1dcfc2e console=ttyS2,1500000n8

then, run

sudo reboot
#4

Using the 4.4 kernel fixed the issue! Thanks!