Acer Aspire 5742g backlight brightness level is not saved on shutdown

[unti1x]

Initial state: backlight brightness is at normal value. Booting to ubuntu, it's still fine. Reboot. Brightness level is set to the lowest possible value. Meanwhile /sys/class/backlight/radeon_bl0/brightness shows 255 as usual. Using keyboard controls or brightness widget fixes it until the next reboot.

The problem appears since 13.04, every release before it including 12.10 and 12.04.2 with kernels up to 3.5.*. Moreover these releases automatically fix the wrong state.

Kernels from 3.8 don't work. I couldn't find any kernels between these versions, they are just disappeared from the wild. The problem also appears in other systems released after 2012 including FreeBSD, OpenBSD, Gentoo, CRUX and HaikuOS. Windows 7 works fine.

It's probably not the problem with radeon driver because I have the same issue with fglrx or without both.

When booting with acpi_backlight=vendor new backlight device named acer-wmi appears. Running the following command changes the actual brightness:
echo 8 > /sys/class/backlight/acer-wmi/brightness

Booting with video.use_bios_initial_backlight=0 doesn't do anything, brightness controls work fine.

Booting with "acpi_osi=" partially fixes the issue: backlight is being restored to the maximal value but not saved on shutdown. Brightness controls work fine but MATE's widget doesn't display the level, only message "No External Display" (acpi_osi=Linux doesn't have this issue).

Booting with video.use_native_backlight=1 doesn't change anything, the controls work fine.

Files from https://wiki.kubuntu.org/Kernel/Debugging/Backlight are attached (I can't attach more than one file so I had to pack them)

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-59-generic 5.4.0-59.65
ProcVersionSignature: Ubuntu 5.4.0-59.65-generic 5.4.78
Uname: Linux 5.4.0-59-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.14
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: unti1x 1121 F.... pulseaudio
 /dev/snd/controlC1: unti1x 1121 F.... pulseaudio
CasperMD5CheckResult: skip
CurrentDesktop: MATE
Date: Sat Jan 23 12:26:04 2021
InstallationDate: Installed on 2021-01-04 (18 days ago)
InstallationMedia: Ubuntu-MATE 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
MachineType: Acer Aspire 5742G
ProcFB: 0 radeondrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-59-generic root=UUID=b0baea2a-cc5b-4ee6-88e7-cce32fd6d019 ro acpi_osi=Linux quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-5.4.0-59-generic N/A
 linux-backports-modules-5.4.0-59-generic N/A
 linux-firmware 1.187.7
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 08/13/2012
dmi.bios.vendor: Acer
dmi.bios.version: V1.30
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: Aspire 5742G
dmi.board.vendor: Acer
dmi.board.version: V1.30
dmi.chassis.type: 10
dmi.chassis.vendor: Acer
dmi.chassis.version: V1.30
dmi.modalias: dmi:bvnAcer:bvrV1.30:bd08/13/2012:svnAcer:pnAspire5742G:pvrV1.30:rvnAcer:rnAspire5742G:rvrV1.30:cvnAcer:ct10:cvrV1.30:
dmi.product.family: Intel_Mobile
dmi.product.name: Aspire 5742G
dmi.product.sku: Calpella_CRB
dmi.product.version: V1.30
dmi.sys.vendor: Acer

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This change was made by a bot.

[Kai-Heng Feng (kaihengfeng)]

Please test latest mainline kernel without "acpi_osi=Linux":
https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.11-rc4/amd64/

[unti1x (unti1x)]

The problem still appears in the latest mainline kernel.

Linux unti1x-laptop 5.11.0-051100rc4-generic #202101180234 SMP Mon Jan 18 02:36:59 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

[Kai-Heng Feng (kaihengfeng)]

Please file a bug against AMD graphics:
https://gitlab.freedesktop.org/drm/amd/issues

[unti1x (unti1x)]

I don't think this is radeon or drm bug: the problem appears with legacy fglrx driver, in custom kernel built without radeon and drm support in rescue mode, and in systems that don't use any of them.

[Kai-Heng Feng (kaihengfeng)]

I think it is, because changing "/sys/class/backlight/radeon_bl0/brightness" by systemd-backlight doesn't work.

So it can be 1) brightness won't be change for first time, or 2) brightness can't be changed early. Either way, it's a driver bug.

[unti1x (unti1x)]

I made a couple more tests and here is what I've found out.

When the backlight is managed by radeon, writing to /sys/class/backlight/radeon_bl0/brightness doesn't do anything. Although changing brightness with Fn+Left/Fn+Right works but the value in /sys/class/backlight/radeon_bl0/brightness doesn't match the actual brightness at all: it can be 250 but the screen would be really dim and vice versa.

When I use the kernel without radeon and drm so the backlight is managed by acpi_video, writing to "/sys/class/backlight/acpi_video0/brightness" works fine, the value is saved and restored properly unless it was set to the maximum.

In both cases the brightness is reset on shutdown to the lowest possible value and it's always the same on the bios boot screen.