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Tasklist

FS#77848 - Acer laptop screen brightness cannot be changed after 6.1.4 kernel upgrade

Attached to Project: Arch Linux
Opened by Brock York (yaspoon) - Tuesday, 14 March 2023, 09:49 GMT
Last edited by Toolybird (Toolybird) - Monday, 27 March 2023, 19:03 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 0
Private No

Details

Description:
Cannot adjust laptop screen brightness using the function key shortcuts OR via echoing values into /sys/class/backlight/acpi0_backlight/brightness when the kernel is 6.1.4 or newer but works perfectly fine with 6.1.3. On a broken kernel Gnome does not even show the brightness bar, as if it is not detected that it is able to be changed.

The laptop in question is an Acer Aspire 4750g with Intel i7-2630qm, Intel HD 3000 gfx and Nvidia 540m.
The nvidia card is disabled in the bios.

I feel like this is an upstream bug but the kernel bug tracker says not to report bugs there unless I've built my own kernel...
Once I get time I'll try and do a git bisect on the kernel versions.


Additional info:
* package version(s)
Kernel versions tried:
6.1.3 - works as intended
6.1.4 - does not work
6.2.2 - does not work
6.2.5 - does not work

Gnome 43.2-1
* config and/or log files etc.
/etc/default/grub has been modified:
GRUB_CMDLINE_LINUX="acpi_backlight=none video=VGA-2:d" - This works on 6.1.3 but not on the other kernel versions

I have also tried the following with the "broken" kernel versions after reading the backlight wiki page:
GRUB_CMDLINE_LINUX="acpi_backlight=vendor"
GRUB_CMDLINE_LINUX="acpi_backlight=native"
GRUB_CMDLINE_LINUX="acpi_backlight=video"

* link to upstream bug report, if any

Steps to reproduce:

Boot laptop with 6.1.4 kernel or newer, attempt to adjust screen brightness using shortcut keys, nothing happens.
This task depends upon

Closed by  Toolybird (Toolybird)
Monday, 27 March 2023, 19:03 GMT
Reason for closing:  Not a bug
Additional comments about closing:  See comments
Comment by Toolybird (Toolybird) - Tuesday, 14 March 2023, 20:24 GMT
> kernel is 6.1.4 or newer but works perfectly fine with 6.1.3

Therefore it's a kernel regression [1]. Also worth checking recent related tickets  FS#77467   FS#77103   FS#77056   FS#73385 

> kernel bug tracker says not to report bugs there

As long as you've done your due diligence then contacting upstream is fine.

[1] https://wiki.archlinux.org/title/Kernel#Debugging_regressions
Comment by Brock York (yaspoon) - Monday, 27 March 2023, 07:22 GMT
Awesome thank you very much for the feedback. I'll checkout the linked wiki and add a link to the upstream bug when I create one.
Comment by Brock York (yaspoon) - Monday, 27 March 2023, 07:49 GMT
Upgrading to kernel 6.2.8 and changing /etc/default/grub
from
GRUB_CMDLINE_LINUX="acpi_backlight=none
to
GRUB_CMDLINE_LINUX="acpi_backlight=native"

Solved the problem! I can adjust the backlight again.
Thank you

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