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#1 2019-08-05 22:30:03

hrkrx
Member
Registered: 2019-08-05
Posts: 2

Backlight and Power management

Hey smile

I have a laptop with arch, but it has a real gpu (2060 RTX) and the screen is connected to DP-2 instead of eDP or Screen0.

As you may have guessed now, the backlight is not working as intended, because i can't adjust it via powermanagement.

I have tried multiple things from adjusting kernel parameters to installing nvidia-bl, or blacklisting stuff (it's a lenovo legion)

I found a reddit post, where someone got the backlight adjusted via "xrandr --output DP-2 --brightness 0..1", so i wrote a pythonscript which can adjust and set the backlight more easily.

I now want to alter the power management to use this script for reading/writing backlight brightness (if you now a better solution i'll gladly try).

how would i achieve that?

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#2 2019-08-06 07:56:38

V1del
Forum Moderator
Registered: 2012-10-16
Posts: 7,256

Re: Backlight and Power management

xrandr doesn't adjust your backlight it just dims the xorg screen, you are not going to save much power. Can you elaborate on "can't adjust it via powermanagement?" which "powermanagement" are you talking about? Nvidia should since a few months have a proper backlight handler enabled, and the relevant node should be accessible in /sys/class/backlight/nvidia_0 in doubt add nvidia.NVreg_EnableBacklightHandler=1 to your kernel params.

If anything you want whatever script you are using to adjust the values there, as that will actually control the backlight.

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#3 2019-08-06 08:14:10

hrkrx
Member
Registered: 2019-08-05
Posts: 2

Re: Backlight and Power management

Thank you for the clarification.

i have the nvidia driver 430, but there is no nvidia_0 folder in /sys/class/backlight (even after adding the kernel param) only acpi_video0 and sadly writing to acpi_video0 does nothing, besides changing the value of the actual_brightness file.

with power management i mean the automatic screen dimming when in battery mode or low on charge.

if it helps here are the full specs of the machine:

Lenovo Legion Y540
i7-9750H
Nvidia RTX 2060
FHD-IPS Display 144Hz

I'd prefer a "normal" solution if possible smile but anything that makes it work will suffice ^^

Last edited by hrkrx (2019-08-06 13:52:02)

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#4 2019-09-03 09:56:29

cccplex
Member
Registered: 2014-01-15
Posts: 7

Re: Backlight and Power management

I also have the y540 but with gtx 1650 using nvidia driver 430.
When bios is set to discrete gpu nothing seems to work. But then I tried switchable graphics and the brightness control works out of the box. It works with "/sys/class/backlight/intel_backlight".
Setting "acpi_backlight=intel_backlight" as kernel option brightness control works running with discrete gpu bios setting. Surprisingly to me it then works with "/sys/class/backlight/acpi_video0"

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