Kde Monitor Backlightslider randomly controls only one, or two, or three monitors

Hello,
I’m using Kde Plasma 5.21.3 with Kernel 5.10.23-1
I have an nvidia card with prop. drivers.
I use 3 external Monitors, and I want to controll their brightness with one slider.
That works with the native Kde “Battery and Brightness” Widget but there’s a problem:
Every time i start the computer a different count of the Monitors will be controlled. Sometimes all three. sometimes only one random one, or two random ones.
If i use DDC control i can still control the Monitors which are not working, but that’s inconvenient.

Does anyone have a hint or idea why the Brightness slider rolls a dice on boot how many screens it controls today?

1 Like

:+1: Welcome to Manjaro! :+1:

  1. Please read this:
    How to provide good information
    and post some more information so we can see what’s really going on. Now we know the symptom of the disease, but we need some more probing to know where the origin lies…

  2. An inxi --admin --verbosity=7 --filter --no-host --width would be the minimum required information… (Personally Identifiable Information like serial numbers and MAC addresses will be filtered out by the above command)
    Also, please copy-paste that output in-between 3 backticks ``` at the beginning and end of the code/text.

  3. The output of xrandr of your three cases would be helpful as well.

:+1:

P.S. If you enter a bit more details in your profile, we can also see which Desktop Environment you’re using, which CPU/GPU or Kernel, … you have without typing it every time

Thank you for your Answer Fabby,
output of inxi :

System:
  Kernel: 5.10.32-1-MANJARO x86_64 bits: 64 compiler: gcc v: 10.2.0 
  parameters: BOOT_IMAGE=/@/boot/vmlinuz-5.10-x86_64 
  root=UUID=fa9a4af6-777a-4e52-8768-207cc178c510 rw rootflags=subvol=@ quiet 
  udev.log_priority=3 
  resume=/dev/disk/by-uuid/fa9a4af6-777a-4e52-8768-207cc178c510 
  resume_offset=2102528 nvidia-drm.modeset=1 nmi_watchdog=0 nowatchdog 
  Desktop: KDE Plasma 5.21.4 tk: Qt 5.15.2 info: latte-dock wm: kwin_x11 vt: 2 
  dm: SDDM Distro: Manjaro Linux base: Arch Linux 
Machine:
  Type: Desktop Mobo: ASRock model: B550M Steel Legend serial: <filter> 
  UEFI: American Megatrends v: P1.80 date: 12/01/2020 
Battery:
  Message: No system battery data found. Is one present? 
Memory:
  RAM: total: 15.56 GiB used: 4.8 GiB (30.9%) 
  RAM Report: permissions: Unable to run dmidecode. Root privileges required. 
CPU:
  Info: 6-Core model: AMD Ryzen 5 3600 bits: 64 type: MT MCP arch: Zen 2 
  family: 17 (23) model-id: 71 (113) stepping: 0 microcode: 8701021 cache: 
  L2: 3 MiB bogomips: 86240 
  Speed: 4102 MHz min/max: 2200/3600 MHz boost: enabled Core speeds (MHz): 
  1: 4102 2: 4133 3: 4182 4: 2077 5: 4026 6: 2090 7: 4175 8: 2084 9: 4104 
  10: 4147 11: 4152 12: 2090 
  Flags: 3dnowprefetch abm adx aes aperfmperf apic arat avic avx avx2 bmi1 
  bmi2 bpext cat_l3 cdp_l3 clflush clflushopt clwb clzero cmov cmp_legacy 
  constant_tsc cpb cpuid cqm cqm_llc cqm_mbm_local cqm_mbm_total cqm_occup_llc 
  cr8_legacy cx16 cx8 de decodeassists extapic extd_apicid f16c flushbyasid 
  fma fpu fsgsbase fxsr fxsr_opt ht hw_pstate ibpb ibs irperf lahf_lm lbrv lm 
  mba mca mce misalignsse mmx mmxext monitor movbe msr mtrr mwaitx nonstop_tsc 
  nopl npt nrip_save nx osvw overflow_recov pae pat pausefilter pclmulqdq 
  pdpe1gb perfctr_core perfctr_llc perfctr_nb pfthreshold pge pni popcnt pse 
  pse36 rdpid rdpru rdrand rdseed rdt_a rdtscp rep_good sep sev sev_es sha_ni 
  skinit smap smca sme smep ssbd sse sse2 sse4_1 sse4_2 sse4a ssse3 stibp 
  succor svm svm_lock syscall tce topoext tsc tsc_scale umip v_vmsave_vmload 
  vgif vmcb_clean vme vmmcall wbnoinvd wdt xgetbv1 xsave xsavec xsaveerptr 
  xsaveopt xsaves 
  Vulnerabilities: Type: itlb_multihit status: Not affected 
  Type: l1tf status: Not affected 
  Type: mds status: Not affected 
  Type: meltdown status: Not affected 
  Type: spec_store_bypass 
  mitigation: Speculative Store Bypass disabled via prctl and seccomp 
  Type: spectre_v1 
  mitigation: usercopy/swapgs barriers and __user pointer sanitization 
  Type: spectre_v2 mitigation: Full AMD retpoline, IBPB: conditional, STIBP: 
  conditional, RSB filling 
  Type: srbds status: Not affected 
  Type: tsx_async_abort status: Not affected 
Graphics:
  Device-1: NVIDIA TU106 [GeForce RTX 2060 Rev. A] vendor: ASUSTeK 
  driver: nvidia v: 460.73.01 alternate: nouveau,nvidia_drm bus-ID: 09:00.0 
  chip-ID: 10de:1f08 class-ID: 0300 
  Device-2: Microdia Webcam Vitade AF type: USB driver: snd-usb-audio,uvcvideo 
  bus-ID: 1-2.4.3:11 chip-ID: 0c45:6366 class-ID: 0102 serial: <filter> 
  Display: x11 server: X.Org 1.20.11 compositor: kwin_x11 driver: 
  loaded: nvidia display-ID: :0 screens: 1 
  Screen-1: 0 s-res: 8560x1440 s-dpi: 108 s-size: 2013x342mm (79.3x13.5") 
  s-diag: 2042mm (80.4") 
  Monitor-1: HDMI-0 res: 2560x1440 dpi: 109 size: 597x336mm (23.5x13.2") 
  diag: 685mm (27") 
  Monitor-2: DP-0 res: 3440x1440 hz: 75 dpi: 109 size: 800x335mm (31.5x13.2") 
  diag: 867mm (34.1") 
  Monitor-3: DP-2 res: 2560x1440 dpi: 109 size: 597x336mm (23.5x13.2") 
  diag: 685mm (27") 
  Message: Unable to show advanced data. Required tool glxinfo missing. 
Audio:
  Device-1: NVIDIA TU106 High Definition Audio vendor: ASUSTeK 
  driver: snd_hda_intel v: kernel bus-ID: 09:00.1 chip-ID: 10de:10f9 
  class-ID: 0403 
  Device-2: AMD Starship/Matisse HD Audio vendor: ASRock driver: snd_hda_intel 
  v: kernel bus-ID: 0b:00.4 chip-ID: 1022:1487 class-ID: 0403 
  Device-3: Realtek USB-C to 3.5mm-Headphone Adapter type: USB 
  driver: hid-generic,snd-usb-audio,usbhid bus-ID: 1-2.3:7 chip-ID: 0bda:4995 
  class-ID: 0300 serial: <filter> 
  Device-4: Microdia Webcam Vitade AF type: USB driver: snd-usb-audio,uvcvideo 
  bus-ID: 1-2.4.3:11 chip-ID: 0c45:6366 class-ID: 0102 serial: <filter> 
  Sound Server-1: ALSA v: k5.10.32-1-MANJARO running: yes 
  Sound Server-2: JACK v: 0.125.0 running: no 
  Sound Server-3: PulseAudio v: 14.2 running: yes 
  Sound Server-4: PipeWire v: 0.3.26 running: yes 
Network:
  Device-1: Intel Wireless-AC 9260 driver: iwlwifi v: kernel bus-ID: 04:00.0 
  chip-ID: 8086:2526 class-ID: 0280 
  IF: wlp4s0 state: down mac: <filter> 
  Device-2: Realtek RTL8125 2.5GbE vendor: ASRock driver: r8169 v: kernel 
  port: f000 bus-ID: 07:00.0 chip-ID: 10ec:8125 class-ID: 0200 
  IF: enp7s0 state: up speed: 1000 Mbps duplex: full mac: <filter> 
  IP v4: <filter> type: dynamic noprefixroute scope: global 
  broadcast: <filter> 
  IP v6: <filter> type: dynamic noprefixroute scope: global 
  IP v6: <filter> type: dynamic noprefixroute scope: global 
  IP v6: <filter> type: noprefixroute scope: link 
  IF-ID-1: br-1ca7876678b8 state: down mac: <filter> 
  IP v4: <filter> scope: global broadcast: <filter> 
  IF-ID-2: br-1ec52863ec7e state: down mac: <filter> 
  IP v4: <filter> scope: global broadcast: <filter> 
  IF-ID-3: br-34c85e09d7d3 state: down mac: <filter> 
  IP v4: <filter> scope: global broadcast: <filter> 
  IF-ID-4: br-70e5dcbc1f1f state: down mac: <filter> 
  IP v4: <filter> scope: global broadcast: <filter> 
  IF-ID-5: br-9664a204375e state: down mac: <filter> 
  IP v4: <filter> scope: global broadcast: <filter> 
  IF-ID-6: br-b7e7c344ce1f state: down mac: <filter> 
  IP v4: <filter> scope: global broadcast: <filter> 
  IF-ID-7: br-ec5122f745d8 state: down mac: <filter> 
  IP v4: <filter> scope: global broadcast: <filter> 
  IF-ID-8: docker0 state: down mac: <filter> 
  IP v4: <filter> scope: global broadcast: <filter> 
  WAN IP: <filter> 
Bluetooth:
  Device-1: Intel Wireless-AC 9260 Bluetooth Adapter type: USB driver: btusb 
  v: 0.8 bus-ID: 1-7.3:6 chip-ID: 8087:0025 class-ID: e001 
  Report: rfkill ID: hci0 rfk-id: 1 state: up address: see --recommends 
Logical:
  Message: No logical block device data found. 
RAID:
  Message: No RAID data found. 
Drives:
  Local Storage: total: 931.51 GiB used: 142.31 GiB (15.3%) 
  SMART Message: Unable to run smartctl. Root privileges required. 
  ID-1: /dev/nvme0n1 maj-min: 259:0 vendor: Gigabyte model: GP-AG41TB 
  size: 931.51 GiB block-size: physical: 512 B logical: 512 B speed: 63.2 Gb/s 
  lanes: 4 rotation: SSD serial: <filter> rev: EGFM11.3 temp: 31.9 C 
  scheme: GPT 
  Message: No optical or floppy data found. 
Partition:
  ID-1: / raw-size: 273.44 GiB size: 273.44 GiB (100.00%) 
  used: 142.28 GiB (52.0%) fs: btrfs dev: /dev/nvme0n1p5 maj-min: 259:5 
  label: N/A uuid: fa9a4af6-777a-4e52-8768-207cc178c510 
  ID-2: /.snapshots raw-size: 273.44 GiB size: 273.44 GiB (100.00%) 
  used: 142.28 GiB (52.0%) fs: btrfs dev: /dev/nvme0n1p5 maj-min: 259:5 
  label: N/A uuid: fa9a4af6-777a-4e52-8768-207cc178c510 
  ID-3: /boot/efi raw-size: 99 MiB size: 95 MiB (95.96%) 
  used: 25.4 MiB (26.8%) fs: vfat dev: /dev/nvme0n1p2 maj-min: 259:2 
  label: N/A uuid: E470-B875 
  ID-4: /btrfs raw-size: 273.44 GiB size: 273.44 GiB (100.00%) 
  used: 142.28 GiB (52.0%) fs: btrfs dev: /dev/nvme0n1p5 maj-min: 259:5 
  label: N/A uuid: fa9a4af6-777a-4e52-8768-207cc178c510 
  ID-5: /home raw-size: 273.44 GiB size: 273.44 GiB (100.00%) 
  used: 142.28 GiB (52.0%) fs: btrfs dev: /dev/nvme0n1p5 maj-min: 259:5 
  label: N/A uuid: fa9a4af6-777a-4e52-8768-207cc178c510 
  ID-6: /home/.snapshots raw-size: 273.44 GiB size: 273.44 GiB (100.00%) 
  used: 142.28 GiB (52.0%) fs: btrfs dev: /dev/nvme0n1p5 maj-min: 259:5 
  label: N/A uuid: fa9a4af6-777a-4e52-8768-207cc178c510 
  ID-7: /home/<filter>/Nextcloud raw-size: 273.44 GiB 
  size: 273.44 GiB (100.00%) used: 142.28 GiB (52.0%) fs: btrfs 
  dev: /dev/nvme0n1p5 maj-min: 259:5 label: N/A 
  uuid: fa9a4af6-777a-4e52-8768-207cc178c510 
  ID-8: /var raw-size: 273.44 GiB size: 273.44 GiB (100.00%) 
  used: 142.28 GiB (52.0%) fs: btrfs dev: /dev/nvme0n1p5 maj-min: 259:5 
  label: N/A uuid: fa9a4af6-777a-4e52-8768-207cc178c510 
Swap:
  Kernel: swappiness: 10 (default 60) cache-pressure: 50 (default 100) 
  ID-1: swap-1 type: partition size: 19.53 GiB used: 0 KiB (0.0%) priority: -2 
  dev: /dev/nvme0n1p6 maj-min: 259:6 label: N/A 
  uuid: bfde55a7-bedf-486b-9eae-20a35d5b3f1f 
Unmounted:
  ID-1: /dev/nvme0n1p1 maj-min: 259:1 size: 529 MiB fs: vfat label: N/A 
  uuid: 7860-556E 
  ID-2: /dev/nvme0n1p3 maj-min: 259:3 size: 16 MiB fs: <superuser required> 
  label: N/A uuid: N/A 
  ID-3: /dev/nvme0n1p4 maj-min: 259:4 size: 637.91 GiB fs: ntfs label: N/A 
  uuid: 8CDC712ADC711026 
USB:
  Hub-1: 1-0:1 info: Full speed (or root) Hub ports: 10 rev: 2.0 
  speed: 480 Mb/s chip-ID: 1d6b:0002 class-ID: 0900 
  Hub-2: 1-2:2 info: Genesys Logic Hub ports: 4 rev: 2.1 speed: 480 Mb/s 
  power: 100mA chip-ID: 05e3:0610 class-ID: 0900 
  Device-1: 1-2.1:4 info: Yubicom Yubikey 4/5 OTP+U2F+CCID 
  type: Keyboard,HID,Smart Card driver: hid-generic,usbhid interfaces: 3 
  rev: 2.0 speed: 12 Mb/s power: 30mA chip-ID: 1050:0407 class-ID: 0b00 
  Device-2: 1-2.3:7 info: Realtek USB-C to 3.5mm-Headphone Adapter 
  type: Audio,HID driver: hid-generic,snd-usb-audio,usbhid interfaces: 4 
  rev: 1.1 speed: 12 Mb/s power: 100mA chip-ID: 0bda:4995 class-ID: 0300 
  serial: <filter> 
  Hub-3: 1-2.4:8 info: Genesys Logic Hub ports: 4 rev: 2.1 speed: 480 Mb/s 
  power: 500mA chip-ID: 05e3:0610 class-ID: 0900 
  Device-1: 1-2.4.1:9 info: Holtek USB Gaming Mouse type: Mouse,Keyboard,HID 
  driver: hid-generic,usbhid interfaces: 3 rev: 2.0 speed: 12 Mb/s 
  power: 100mA chip-ID: 04d9:a259 class-ID: 0300 
  Device-2: 1-2.4.2:10 info: Apple Aluminium Keyboard (ISO) 
  type: Keyboard,Mouse driver: apple,usbhid interfaces: 2 rev: 2.0 
  speed: 12 Mb/s power: 100mA chip-ID: 05ac:0250 class-ID: 0301 
  Device-3: 1-2.4.3:11 info: Microdia Webcam Vitade AF type: Video,Audio 
  driver: snd-usb-audio,uvcvideo interfaces: 4 rev: 2.0 speed: 480 Mb/s 
  power: 500mA chip-ID: 0c45:6366 class-ID: 0102 serial: <filter> 
  Hub-4: 1-2.4.4:12 info: Genesys Logic Hub ports: 4 rev: 2.1 speed: 480 Mb/s 
  power: 100mA chip-ID: 05e3:0610 class-ID: 0900 
  Hub-5: 1-7:3 info: Genesys Logic Hub ports: 4 rev: 2.0 speed: 480 Mb/s 
  power: 100mA chip-ID: 05e3:0610 class-ID: 0900 
  Device-1: 1-7.3:6 info: Intel Wireless-AC 9260 Bluetooth Adapter 
  type: Bluetooth driver: btusb interfaces: 2 rev: 2.0 speed: 12 Mb/s 
  power: 100mA chip-ID: 8087:0025 class-ID: e001 
  Device-2: 1-8:5 info: ASRock LED Controller type: HID 
  driver: hid-generic,usbhid interfaces: 1 rev: 1.1 speed: 12 Mb/s 
  power: 100mA chip-ID: 26ce:01a2 class-ID: 0300 serial: <filter> 
  Hub-6: 2-0:1 info: Full speed (or root) Hub ports: 4 rev: 3.1 speed: 10 Gb/s 
  chip-ID: 1d6b:0003 class-ID: 0900 
  Hub-7: 2-2:2 info: Genesys Logic Hub ports: 4 rev: 3.1 speed: 5 Gb/s 
  chip-ID: 05e3:0612 class-ID: 0900 
  Hub-8: 2-2.4:3 info: Genesys Logic Hub ports: 4 rev: 3.1 speed: 5 Gb/s 
  chip-ID: 05e3:0612 class-ID: 0900 
  Hub-9: 2-2.4.4:4 info: Genesys Logic USB3.0 Hub ports: 4 rev: 3.0 
  speed: 5 Gb/s chip-ID: 05e3:0620 class-ID: 0900 
  Device-1: 2-2.4.4.4:5 info: Norelsys NS1081 type: Mass Storage 
  driver: usb-storage interfaces: 1 rev: 3.0 speed: 5 Gb/s power: 8mA 
  chip-ID: 2537:1081 class-ID: 0806 serial: <filter> 
  Hub-10: 3-0:1 info: Full speed (or root) Hub ports: 2 rev: 2.0 
  speed: 480 Mb/s chip-ID: 1d6b:0002 class-ID: 0900 
  Hub-11: 4-0:1 info: Full speed (or root) Hub ports: 4 rev: 3.1 
  speed: 10 Gb/s chip-ID: 1d6b:0003 class-ID: 0900 
  Hub-12: 5-0:1 info: Full speed (or root) Hub ports: 4 rev: 2.0 
  speed: 480 Mb/s chip-ID: 1d6b:0002 class-ID: 0900 
  Hub-13: 5-2:2 info: ASMedia ASM1074 High-Speed hub ports: 4 rev: 2.1 
  speed: 480 Mb/s power: 100mA chip-ID: 174c:2074 class-ID: 0900 
  Hub-14: 6-0:1 info: Full speed (or root) Hub ports: 4 rev: 3.1 
  speed: 10 Gb/s chip-ID: 1d6b:0003 class-ID: 0900 
  Hub-15: 6-2:2 info: ASMedia ASM1074 SuperSpeed hub ports: 4 rev: 3.0 
  speed: 5 Gb/s power: 8mA chip-ID: 174c:3074 class-ID: 0900 
Sensors:
  System Temperatures: cpu: 56.8 C mobo: 32.0 C gpu: nvidia temp: 41 C 
  Fan Speeds (RPM): fan-1: 0 fan-2: 531 fan-3: 1515 fan-4: 312 fan-5: 0 
  fan-6: 0 fan-7: 211 gpu: nvidia fan: 0% 
Info:
  Processes: 420 Uptime: 6m wakeups: 0 Init: systemd v: 247 tool: systemctl 
  Compilers: gcc: 10.2.0 Packages: 1610 pacman: 1600 lib: 350 flatpak: 10 
  Shell: Zsh v: 5.8 running-in: yakuake inxi: 3.3.04

xrandr:

Screen 0: minimum 8 x 8, current 8560 x 1440, maximum 32767 x 32767
HDMI-0 connected 2560x1440+6000+0 (normal left inverted right x axis y axis) 597mm x 336mm
   2560x1440     59.95 +  74.97* 
   1920x1080     74.97    60.00    59.94    50.00  
   1680x1050     59.95  
   1440x900      59.89  
   1280x1440     59.91  
   1280x1024     75.02    60.02  
   1280x960      60.00  
   1280x720      60.00    59.94    50.00  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    72.81    59.94    59.93  
DP-0 connected primary 3440x1440+2560+0 (normal left inverted right x axis y axis) 800mm x 335mm
   3440x1440     75.05*+ 143.92   120.00    99.98  
   2560x1440    120.00    59.95  
   2048x1152     60.00  
   1920x1200     59.88  
   1920x1080    119.98   119.88    60.00    59.94    50.00  
   1720x1440     59.98  
   1680x1050     59.95  
   1600x1200     60.00  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      59.94  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    72.81    59.94    59.93  
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 connected 2560x1440+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
   2560x1440     59.95 +  74.97* 
   1920x1080     74.97    60.00    59.94    50.00  
   1680x1050     59.95  
   1440x900      59.89  
   1280x1440     59.91  
   1280x1024     75.02    60.02  
   1280x960      60.00  
   1280x720      60.00    59.94    50.00  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    72.81    59.94    59.93  
DP-3 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)

That all looks OK.

  1. What is DDC control? (link)

  2. What does the keyboard combo do compared to the brightness slider from KDE (I suppose in system settings)

  3. What"'s the output of

    ls /sys/class/backlight
    

    in the case of all monitors working compared to just a few?

  1. DDC control: GitHub - ddccontrol/ddccontrol: DDC Control
    basically a gui to change settings in external monitors

  2. for the brightness slider i use the “Battery and Brightness” widget from kde. It behaves exactly the same for me as the keyboard combo

3.1 two outer ones working, middle one not:

ls /sys/class/backlight
total 0
drwxr-xr-x  2 root root 0 May  5 18:05 .
drwxr-xr-x 72 root root 0 May  5 13:31 ..

3.2 all monitors working:

ls /sys/class/backlight
total 0
drwxr-xr-x  2 root root 0 May  5 20:29 .
drwxr-xr-x 72 root root 0 May  5 13:31 ..

Are these folders supposed to be empty?

Also i noticed that the behavior of the monitor is not only changing on reboots, but also if the pc was in sleep state or even if just the screens where turned off by the energy saving settings.

No they’re not:

ls /sys/class/backlight/
nvidia_0

Can I get the output of these 2 commands:

nvidia-smi | head
mhwd --listinstalled

:thinking:

nvidia-smi:

Fri May  7 13:42:46 2021       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 460.73.01    Driver Version: 460.73.01    CUDA Version: 11.2     |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|                               |                      |               MIG M. |
|===============================+======================+======================|
|   0  GeForce RTX 2060    Off  | 00000000:09:00.0  On |                  N/A |
|  0%   44C    P0    46W / 160W |   1461MiB /  5931MiB |      1%      Default |

mhwd --listinstalled:

> Installed PCI configs:
--------------------------------------------------------------------------------
                  NAME               VERSION          FREEDRIVER           TYPE
--------------------------------------------------------------------------------
          video-nvidia            2020.11.30               false            PCI


Warning: No installed USB configs!

Yeah, all that looks normal, but you still have nothing in the /sys/class/backlight directory, so I’m at a loss on how to help you any further… Sorry!

:sob:

As you guessed, it’s still empty…
Anyways, thanks for your help

1 Like

Found something!

Can you try adding video.use_native_backlight=1 to your kernel parameters?

If you don’t know how to do that, shout out!

:crossed_fingers:

I have added the parameter and my screens seem to be working now, but /sys/class/backlight is still empty. I will test it for a few days and reply again

Thanks for your help!

1 Like

I still sometimes experience the situation where one monitor won’t change its brightness, but i noticed it will eventually work if i play around with the slider for a while (or my keyboard shortcut).
For example: I turn the brightness up and down a few times and suddenly the monitor which wasn’t working starts changing its brightness.
The good thing: after the third monitor starts working, it will work normally until i reboot or sleep my machine.

Can you try adding video.use_native_backlight=1 to your kernel parameters?

Since it started to work more or less reliably now, I will mark this as answer.
Thanks for your help :smiley:

1 Like

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