FS#77467 - Backlight on Dell AMD/Nvidia laptop doesn't work with linux-6.1 kernels

Attached to Project: Arch Linux
Opened by Bruce Guenter (bruceg) - Sunday, 12 February 2023, 00:50 GMT
Last edited by Toolybird (Toolybird) - Thursday, 16 February 2023, 03:32 GMT
Task Type Bug Report
Category Kernel
Status Closed
Assigned To No-one
Architecture x86_64
Severity Low
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 2
Private No

Details

Description:

I have a Dell 5515 AMD laptop, which has both an integrated and an Nvidia GPU. The linux-6.1 kernel series appears to have regressed the backlight control.

On the linux-6.0 kernel series, two backlights appear in /sys/class/backlight: amdgpu_bl0 and nvidia_wmi_ec_backlight. The former appears to be a dummy device present on the iGPU but not actually attached to anything. It is the latter that controls the display panel backlight.

On the linux-6.1 kernel series, I have been unable to get the nvidia backlight control to appear. The nvidia_wmi_ec_backlight module loads, prints nothing, but the control doesn't work.

With acpi_backlight=native or no acpi_backlight option, only amdgpu_bl0 appears
With acpi_backlight=video, only acpi_video0 appears
With acpi_backlight=vendor, no backlight controls are present at all.

Additional info:
* package version(s) linux-6.1 through linux-6.1.1
* I have not yet filed a bug upstream, as they have directed me to report it here first
* This happens both with or without the proprietary nvidia module loaded, or even installed, so it's not an issue with that code.

Steps to reproduce:
* Boot affected kernel
* Log in to desktop environment
* Attempt to use backlight controls
This task depends upon

Closed by  Toolybird (Toolybird)
Thursday, 16 February 2023, 03:32 GMT
Reason for closing:  Upstream
Additional comments about closing:  Reporter says "Found an adequate workaround"
Comment by Bruce Guenter (bruceg) - Sunday, 12 February 2023, 00:51 GMT
I mistyped, that should read a Dell G15 5515 laptop.

The related forum thread is here: https://bbs.archlinux.org/viewtopic.php?pid=2081999
Comment by Bruce Guenter (bruceg) - Tuesday, 14 February 2023, 03:24 GMT
I mistyped, that should read a Dell G15 5515 laptop.

The related forum thread is here: https://bbs.archlinux.org/viewtopic.php?pid=2081999
Comment by Bruce Guenter (bruceg) - Tuesday, 14 February 2023, 05:16 GMT
Reported upstream: https://bugzilla.kernel.org/show_bug.cgi?id=216138
Comment by Bruce Guenter (bruceg) - Wednesday, 15 February 2023, 04:41 GMT
Adding acpi_backlight=nvidia_wmi_ec to the kernel command line is a functional workaround for me, so this can be closed.

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