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#1 2021-07-21 12:53:35

Rogrir
Member
Registered: 2021-07-21
Posts: 6

Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

Problem is I can't change backlight and it is always set to 100% (from visibility standpoint).

I tried absolutely every post I could find about backlight like for example https://askubuntu.com/questions/1217133 … egion-y540 with every other solution and many more. I haven't seen any post with the exact problem I have.

Xrandr works properly but it just changes gamma not the real values. When editing "/sys/class/backlight/acpi_video0/brightness" or "/sys/class/backlight/amdgpu_bl0/brightness" values change properly with no visible effect.
I also have passed "acpi_backlight=video nvidia.NVreg_RegistryDwords=EnableBrightnessControl=1" to kernel.
Without the "acpi_backlight=video" acpi doesn't load properly on boot. Systemctl errors that acpi_video0 wasn't found.

On boot I get message:

ACPI Error: AE_NOT_FOUND, During name lookup/catalog (20210331/psobject-220)
ACPI BIOS Error (bug): Could not resolve symbol [\_SB.PCI0.PB2], AE_NOT_FOUND (20210331/dswload2-162)

and this is also the same message that exists in journalctl.

It might be possible that this can only be fixed by BIOS update but I need confirmation.

Relevant neofetch information:

OS: Arch Linux x86_64
Host: 82JU Legion 5 15ACH6H
Kernel: 5.13.4-arch1-1
WM: dwm
Terminal: st
CPU: AMD Ryzen 7 5800H with Radeon Graphics (16) @ 3.200GHz
GPU: NVIDIA GeForce RTX 3060 Mobile / Max-Q
GPU: AMD ATI 06:00.0 Cezanne
Memory: 3154MiB / 15368MiB

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#2 2021-08-18 14:45:51

whenov
Member
Registered: 2011-07-03
Posts: 10

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

Have you tried "amdgpu.backlight=0"?

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#3 2021-08-18 14:49:28

Rogrir
Member
Registered: 2021-07-21
Posts: 6

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

As an kernel parameter or as an variable for xorg?

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#4 2021-08-18 15:03:21

whenov
Member
Registered: 2011-07-03
Posts: 10

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

Rogrir wrote:

As an kernel parameter or as an variable for xorg?

As a kernel parameter.

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#5 2021-08-18 15:16:40

Rogrir
Member
Registered: 2021-07-21
Posts: 6

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

According to this https://www.kernel.org/doc/html/latest/ … eters.html I don't see it as an kernel parameter but will try wink

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#6 2021-08-18 16:23:38

whenov
Member
Registered: 2011-07-03
Posts: 10

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

It is actually a module parameter.

Check "modinfo amdgpu|grep backlight" and https://gitlab.freedesktop.org/drm/amd/-/issues/1438

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#7 2021-08-19 18:46:16

Rogrir
Member
Registered: 2021-07-21
Posts: 6

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

Unfortunately it did not help, but I will look closer into this parameters.

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#8 2021-08-19 20:27:50

d_fajardo
Member
Registered: 2017-07-28
Posts: 1,563

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

Have a look at this.

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#9 2021-09-03 07:50:37

cyberemond
Member
Registered: 2021-09-03
Posts: 3

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

I have the same laptop (15ACH6H, 5800H, 3060, 16GB RAM), and I've tried everything so far. Kernel parameters, various GPU configurations with optimus-manager, etc.

The only scenario in which the backlight works is when I set it to use the nVidia card in the BIOS. But that eats up a hell of a lot of battery, and is thus not a real solution.

Has anyone found a solution that lets the integrated chip do its job?

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#10 2021-09-03 07:52:18

Rogrir
Member
Registered: 2021-07-21
Posts: 6

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

You mean as a Dynamic GPU? If yes then it doesn't even work for me.

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#11 2021-09-03 18:10:28

cyberemond
Member
Registered: 2021-09-03
Posts: 3

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

When you set dynamic GPU in the BIOS, everything is routed through the AMD chip (including what the nvidia card renders). When you set dedicated, the nvidia chip does everything.

Brightness control outright doesn't work if the AMD chip is involved at all. Nvidia on its own works fine, but eats up battery like crazy.

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#12 2021-09-03 18:33:22

Rogrir
Member
Registered: 2021-07-21
Posts: 6

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

But when I set it to the other one everything lags horribly even my bootloader and linux won't even load itself. It just hangs in the loading screen.

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#13 2021-09-03 18:52:38

cyberemond
Member
Registered: 2021-09-03
Posts: 3

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

That genuinely sounds like a hardware problem. You should be able to boot and get a graphical session from the base Arch install, without any further modifications.

Does it work on other distros/ OS's?

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#14 2023-04-19 22:04:13

somso2e
Member
Registered: 2023-04-19
Posts: 1

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

I'm on ubuntu22.04 and have the exact laptop as the OP. I can change the backlight using the fn hotkeys on gnome. But I can't change it using xbacklight.

I did found a repo on github that got recently deprecated as of me writing this but it still works fine for me. *Use at your own risk*
https://github.com/haikarainen/light
Upon manually checking the value in `/sys/class/backlight/nvidia_wmi_ec_backlight/brightness`, it does seem that is actually changing it rather than some hacky way of changing the gamma rate like the --brighness option in xrandr.

If someone has found a better way of changing the brightness, please share.

OS: Ubuntu 22.04.2 LTS x86_64
Host: 82JU Legion 5 15ACH6H
Kernel: 6.2.11-060211-generic
DE: i3-with-shmlog
WM: i3
CPU: AMD Ryzen 7 5800H with Radeon Graphics (16) @ 3.200GHz
GPU: AMD ATI 05:00.0 Cezanne
GPU: NVIDIA GeForce RTX 3060 Mobile / Max-Q
Memory: 5544MiB / 13818MiB

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#15 2023-04-19 22:43:57

2ManyDogs
Forum Moderator
Registered: 2012-01-15
Posts: 4,645

Re: Backlight not working [\_SB.PCI0.PB2], AE_NOT_FOUND

somso2e, Ubuntu is not supported here; this was made clear when you registered:

Forum Registration wrote:

These forums are for Arch Linux x86_64 ONLY.

Not Artix, or Apricity, or Manjaro, or any of the "easy Arch installers", nor Arch-ARM; nothing other than vanilla 64-bit Arch Linux. Ask those communities for support.
If you have installed Arch, please read the rules before posting. README: Forum Rules.

Please note, that in signing up to these forums, you agree to the Arch Linux Privacy Policy, and any information you post to these boards will be considered "public information". README: Forum Rules.

In addition, this thread is almost two years old and the OP has not been back since 2021. Please do not necrobump.

Closing this old thread.


How to post. A sincere effort to use modest and proper language and grammar is a sign of respect toward the community.

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