Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0

Question

As what title shows, I see this message at the screen of booting system.

[ OK ] Created slice system-systemd\x2dbacklight.slice.
       Starting Load/Save Screen Backlight Brightness of backlight:acpi_video0
       Starting Load/Save Screen Backlight Brightness of backlight:amdgpu_bl0
[FAILED] Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0
See 'systemctl status systemd-backlight@backlight:acpi_video0.service' for details.

and my screen brightness always reset to max value after reboot. (I just added echo 80 > /sys/class/backlight/amdgpu_bl0/brightness to temporarily solve this before)

after booting i just run sudo systemctl status systemd-backlight@backlight:acpi_video0.service and get a output:

● systemd-backlight@backlight:acpi_video0.service - Load/Save Screen Backlight Brightness of backlight:acpi_video0
     Loaded: loaded (/lib/systemd/system/[email protected]; static; vendor preset: enabled)
     Active: failed (Result: exit-code) since Wed 2021-02-10 14:17:56 CST; 1min 15s ago
       Docs: man:[email protected](8)
    Process: 822 ExecStart=/lib/systemd/systemd-backlight load backlight:acpi_video0 (code=exited, status=1/FAILURE)
   Main PID: 822 (code=exited, status=1/FAILURE)

Feb 10 14:17:56 q-laptop systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:acpi_video0...
Feb 10 14:17:56 q-laptop systemd-backlight[822]: Failed to get backlight or LED device 'backlight:acpi_video0': No such device
Feb 10 14:17:56 q-laptop systemd[1]: systemd-backlight@backlight:acpi_video0.service: Main process exited, code=exited, status=1/FAILURE
Feb 10 14:17:56 q-laptop systemd[1]: systemd-backlight@backlight:acpi_video0.service: Failed with result 'exit-code'.
Feb 10 14:17:56 q-laptop systemd[1]: Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0.

after that i run sudo systemctl status systemd-backlight@backlight:amdgpu_bl0 then i get output:

● systemd-backlight@backlight:amdgpu_bl0.service - Load/Save Screen Backlight Brightness of backlight:amdgpu_bl0
     Loaded: loaded (/lib/systemd/system/[email protected]; static; vendor preset: enabled)
     Active: active (exited) since Wed 2021-02-10 14:17:56 CST; 7min ago
       Docs: man:[email protected](8)
    Process: 824 ExecStart=/lib/systemd/systemd-backlight load backlight:amdgpu_bl0 (code=exited, status=0/SUCCESS)
   Main PID: 824 (code=exited, status=0/SUCCESS)

Feb 10 14:17:56 q-laptop systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:amdgpu_bl0...
Feb 10 14:17:56 q-laptop systemd[1]: Finished Load/Save Screen Backlight Brightness of backlight:amdgpu_bl0.

I'm new in Linux. I want to know what happened while my system booting. Does it has relation between the failed message and my screen brightness which always be reset after system rebooted? How to remove this error message?

My system is Ubuntu 20.04LTS.

thanks in advance.

Answer 1

From what I have researched ACPI (Advanced Configuration Power Interface) is and has been riddled with security risks and hacks from its beginnings. Linus Torvalds has made statements about these calling it "A Disaster" two decades ago.

In the meantime AMD purchased Radeon and began incorporating graphics processors GPUs into the AMD processors rather than wasting space and propagation times to run through a PCI controller to run a graphics controller.

Many proprietary graphics drivers were conflicting with Linux Kernel modules literally rendering computers useless to users requiring many different manual work-arounds and even some GNU licensed drivers to install

Linux decided to create its own GPU module into the Kernel to run the graphics controller, this may be the case whether you have an Intel or an AMD processor, I am not certain of this.

If you look at the code in your question you can see that first there is an attempt by systemd to start the ACPI_Video0 followed by another attempt to start the AMDgpu_Bl0.

The ACPI_video0 fails but the AMDgpu_Bl0 does not. Journalctl shows the ACPI_Video0 failure but does not list the AMDgpu_Bl0 as failed but Active.

This is as far as I can answer this portion of your question.

As to the reason your screen is reset to full brightness I would guess the kernel module that runs the graphics is likely buggy until it is further developed. It has only recently been added to Kernels. I have the same ACPI_Video0 error every reboot but I do not have the reset brightness you experience. In any case I cannot find a bug listed that matches your description of full brightness reset.

I will update this answer as I research it further, along with sources of information.