Arch Linux

lana_gecko

Member

Registered: 2020-10-06

Posts: 4

Can't control brightness on Lenovo Legion Y740

I've been struggling with this for two months. The problem is that when I call `xbacklight` the value in `/sys/class/backlight/intel_backlight/actual_brightness` changes but nothing happens except when the value reaches 0, in that case the screen turns black.

I have set up optimus manager to switch from intel graphics to nvidia in order to save battery. The behaviour is the same using intel graphics or nvidia.

From the Backlight page of the arch wiki I have tried the following :

* changing the value of `acpi_backlight` to `vendor`, `video`, `native` and `none`.
* the xbacklightmon script
* setting i915.enable_dpcd_backlight=1

I also tried to set the value of `acpi_osi` to `Linux`, `Windows2009` and `Windows2015`, but still no backlight.

I have installed `mesa`, `lib32-mesa`, `xf86-video-intel` et `nvidia` packages.

My system info :
Laptop : Lenovo Legion Y740
CPU : Intel i7-9750H
GPU : Intel UHD Graphics 630
GPU : NVIDIA RTX 2070 Max-Q
kernel : 5.8.12-arch1-1

Slithery

Administrator

From: Norfolk, UK

Registered: 2013-12-01

Posts: 5,776

Re: Can't control brightness on Lenovo Legion Y740

Which DE/WM are you running? Is this Wayland?

---

No, it didn't "fix" anything. It just shifted the brokeness one space to the right. - jasonwryan
Closing -- for deletion; Banning -- for muppetry. - jasonwryan

aur - dotfiles

lana_gecko

Member

Registered: 2020-10-06

Posts: 4

Re: Can't control brightness on Lenovo Legion Y740

I'm using i3wm with X.

fistrosan

Member

Registered: 2020-04-01

Posts: 171

Re: Can't control brightness on Lenovo Legion Y740

I also have a Lenovo (albeit X1) with intel UHD 630 and can control my backlight correctly by changing the value of

/sys/class/backlight/intel_backlight/brightness

One possibility is to simply consider that the human eye sees light levels in a logarithmic scale, meaning that only large changes in brightness are noticed. For instance, according to

/sys/class/backlight/intel_backlight/max_brightness

My maximum brightness is about 24000. Changing to 10000 has barely any effect. Only when  start hitting values < 1000 I see actual changes in brightness. With 0, just like you, I get a blank screen.

The other thing that comes to my mind after reading the archwiki is the paragraph that states:

"On Nvidia Optimus laptops, the kernel parameter nomodeset can interfere with the ability to adjust the backlight."

Since you have such a optimus laptop, maybe you can check your kernel parameters ?

sysctl -a | grep nomodeset

lana_gecko

Member

Registered: 2020-10-06

Posts: 4

Re: Can't control brightness on Lenovo Legion Y740

I do not have the kernel parameter nomodeset, I checked with the command you gave me.

Changing the value of

/sys/class/backlight/intel_backlight/brightness

does not have any effect even with a very low value (like 1), when I do it manually (echo) or with xbacklight.

My father too has an X1 and it works without any problem.

I looks like this value is not read or that some how it does not end up where it needs to be but I have no idea how I could track this to know where the problem comes from.
It does not look like it is arch specific though, I have tried to boot on an Ubuntu live stick and I have  the same issue. But it works when I boot on my Windows partition.

I forgot to mention that I have an eDP screen, I do not know if it changes the problem.

Last edited by lana_gecko (2020-10-08 10:20:02)

cupid_stunt

Member

Registered: 2020-08-15

Posts: 21

Re: Can't control brightness on Lenovo Legion Y740

Same issue here. Same laptop(ish), same situation, looking for the same solution.

01:00.0 VGA compatible controller: NVIDIA Corporation TU117M [GeForce GTX 1650 Mobile / Max-Q] (rev a1)

No Intel card.
Maybe there is some kernel module that needs loading? (highly doubt it)

lana_gecko

Member

Registered: 2020-10-06

Posts: 4

Re: Can't control brightness on Lenovo Legion Y740

It is not the same issue. The issue here is that the backlight (brightness) does not change with nvidia nor intel card.

But since I had the same one when I got my computer, I wll help.
If you can not see the Intel card with the command

lspci | grep VGA

you should check the BIOS settings and make sure you are using "Swichable graphics".

Be careful though changing BIOS settings can prevent you from booting on your arch partition (reverting will work) you might need to reinstall arch with the correct BIOS settings enabled.