After following https://wiki.ubuntu.com/Kernel/Debugging/Backlight I have these results regarding when backlight controls (on laptop AND on an external keybaord) operate in either GDM (login screen) and/or XFCE logged in session:
With GRUB_CMDLINE_LINUX set to:
* no options: GDM but not in XFCE session
* acpi_backlight=vendor : neither
* video.use_bios_initial_backlight=0 : GDM but not session (system seems slower)
* acpi_osi= : works in both (sometimes doesn't after reboot, possibly if not plugged in)
* video.use_native_backlight=1 : gdm but not session
* /usr/share/X11/xorg.conf.d/80-backlight.conf : works in both. Default XFCE background image looks funny (vertical stripes).
XFCE power manager's backlight brightness level indicator appears and changes with all of the above (but actual backlight brightness only changes with some of the settings as mentioned above)
`echo 8 > /sys/class/backlight/intel_backlight/brightness` seems to always work.
ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: linux-image-5.15.0-69-generic 5.15.0-69.76
ProcVersionSignature: Ubuntu 5.15.0-69.76-generic 5.15.87
Uname: Linux 5.15.0-69-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.4
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: akom 2728 F.... pulseaudio
/dev/snd/controlC1: akom 2728 F.... pulseaudio
CasperMD5CheckResult: unknown
CurrentDesktop: XFCE
Date: Sun Apr 16 10:10:54 2023
InstallationDate: Installed on 2017-05-10 (2166 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
MachineType: Dell Inc. Precision 7510
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.15.0-69-generic root=UUID=fd5209d3-739b-4fdb-a117-4bd62009cd34 ro
RelatedPackageVersions:
linux-restricted-modules-5.15.0-69-generic N/A
linux-backports-modules-5.15.0-69-generic N/A
linux-firmware 20220329.git681281e4-0ubuntu3.12
SourcePackage: linux
UpgradeStatus: Upgraded to jammy on 2022-08-19 (240 days ago)
dmi.bios.date: 11/17/2022
dmi.bios.release: 1.30
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.30.3
dmi.board.name: 0M1YNP
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.asset.tag: 204286
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr1.30.3:bd11/17/2022:br1.30:svnDellInc.:pnPrecision7510:pvr:rvnDellInc.:rn0M1YNP:rvrA00:cvnDellInc.:ct9:cvr:sku06D9:
dmi.product.family: Precision
dmi.product.name: Precision 7510
dmi.product.sku: 06D9
dmi.sys.vendor: Dell Inc.
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