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#1 2018-05-05 12:09:13

DeadLink404
Member
Registered: 2017-11-24
Posts: 41

[Solved] Backlight control on Optimus Laptop

I have an i820HK + gtx 1070 laptop with arch installed.
(Clevo P651-HS).
When booting in MsHybrid (optimus) mode I am unable to control brightness (weather using prime or bumblebee).
Currently I have bumblebee configured as that is the setup I'd like to get functioning.
The sysfs changes appropriately in any case but only at 0 this does anything (backlight switches off )and everything above turns the brightness to 100%.

When booting with the integrated card disabled I can change the brightness when using the proprietary drivers (nouveau does not work).
In windows it works in MsHybrid too and disabling the integrated card in the device manager breaks it, so the intel graphics driver is the one in charge of the brightness in MsHybrid mode.

I have tried all the acpi_backlight options and while some do add the acpi_video0 interface it is functionally identical to the intel one, except it does nothing when set to 0 as well.
Xbacklight also just changes the sysfs without any change to brightness.

Because of the lspci lockup issue I have to use acpi_osi="!Windows 2015" or acpi_osi=! acpi_osi="Windows 2009" kernel parameters (both work as workaround).

What more can I do?

uname -r

4.16.6-1-ARCH

dmesg

Modules=(i915 bbswitch)

Problem persists on 4.16.9-1-ARCH

Last edited by DeadLink404 (2018-05-20 17:42:54)

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#2 2018-05-05 14:56:33

V1del
Forum Moderator
Registered: 2012-10-16
Posts: 23,319

Re: [Solved] Backlight control on Optimus Laptop

Verify that you aren't incidentally affected by https://bbs.archlinux.org/viewtopic.php … 9#p1782219

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#3 2018-05-06 11:33:33

DeadLink404
Member
Registered: 2017-11-24
Posts: 41

Re: [Solved] Backlight control on Optimus Laptop

That is not my issue, as the interfaces register as expected and are affected by keyboard shortcuts. For me the brightness in /sys/class/backlight/*/brightness changes but the screen doesn't.
The acpi_video0 interface is even more useless than the intel one as a brightness of 0 gives a black screen only for intel_brightness.

Just to be sure I did add video.only_lcd=0 but as expected it didn't fix it.

Last edited by DeadLink404 (2018-05-20 15:35:46)

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#4 2018-05-20 17:42:38

DeadLink404
Member
Registered: 2017-11-24
Posts: 41

Re: [Solved] Backlight control on Optimus Laptop

Ok after some looking I stumbled over the i915.enable_dpcd_backlight=1 kernel parameter.
Which hurray makes the /sys/class/backlight/intel_backlight/brightness work.
I have an integrated eDP TN Panel.
I think the option enables Aux over eDP instead of using pwm, but I am not sure what exactly it does.
To anybody that does consider adding it to the backlight wiki. I had a hard Time finding this solution.

The max_brightness is now too high but that is a story for another thread I guess.

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#5 2024-08-23 11:00:10

shashankrajora2002
Member
Registered: 2024-08-23
Posts: 1

Re: [Solved] Backlight control on Optimus Laptop

DeadLink404 wrote:

Ok after some looking I stumbled over the i915.enable_dpcd_backlight=1 kernel parameter.
Which hurray makes the /sys/class/backlight/intel_backlight/brightness work.
I have an integrated eDP TN Panel.
I think the option enables Aux over eDP instead of using pwm, but I am not sure what exactly it does.
To anybody that does consider adding it to the backlight wiki. I had a hard Time finding this solution.

The max_brightness is now too high but that is a story for another thread I guess.

Hi there, I am facing the same issue currently, even after trying your fix, and as many as I could google, I couldn't get brightness change to work when in Optimus mode. In Nvidia-only mode, however, the brightness control is working perfectly fine... Can you help me here ??

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#6 2024-08-23 11:26:41

DeadLink404
Member
Registered: 2017-11-24
Posts: 41

Re: [Solved] Backlight control on Optimus Laptop

shashankrajora2002 wrote:

Hi there, I am facing the same issue currently

I doubt it. If it was exactly the same issue the fix would have worked.

Create a new Post, include dmesg and lspci output.
Also note which interfaces appear in /sys/class/backlight.
Also xrandr | grep eDP to see if the display is connected over embedded Display Port.

If you have a vesa interface (acpi_video0) try setting i915.enable_dpcd_backlight to 2 to force i915 to use that interface, maybe that works.

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#7 2024-08-23 11:53:43

V1del
Forum Moderator
Registered: 2012-10-16
Posts: 23,319

Re: [Solved] Backlight control on Optimus Laptop

Also note that this post is 6 years old, a LOT will have changed  between that time.

Please don't necrobump old threads: https://wiki.archlinux.org/title/Genera … bumping%22

Make a new one and include those outputs asked for

Closing this old thread.

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