Lenovo Ideapad L340 screen backlight stuck at maximum brightness

[Elijah Rockers]

acpi_osi=Linux and acpi_backlight=vendor do not fix. Depending on the kernel parameters, /sys/class/backlight contains either "acpi_video0" or "ideapad". I have also tried acpi_backlight=none

ls /sys/class/backlight:
acpi_video0

grep -r . /proc/acpi
/proc/acpi/button/lid/LID/state:state: open
/proc/acpi/wakeup:Device S-state Status Sysfs node
/proc/acpi/wakeup:GPP0 S3 *disabled
/proc/acpi/wakeup:GPP1 S3 *enabled pci:0000:00:01.2
/proc/acpi/wakeup:GPP2 S3 *enabled pci:0000:00:01.3
/proc/acpi/wakeup:GPP3 S3 *disabled
/proc/acpi/wakeup:GPP4 S3 *disabled
/proc/acpi/wakeup:GPP5 S3 *disabled
/proc/acpi/wakeup:GPP6 S3 *disabled
/proc/acpi/wakeup:GP17 S3 *enabled pci:0000:00:08.1
/proc/acpi/wakeup:XHC0 S3 *enabled pci:0000:03:00.3
/proc/acpi/wakeup:XHC1 S3 *enabled pci:0000:03:00.4
/proc/acpi/wakeup:GP18 S3 *enabled pci:0000:00:08.2

iasl -d dsdt.dat
Intel ACPI Component Architecture
ASL+ Optimizing Compiler/Disassembler version 20180105
Copyright (c) 2000 - 2018 Intel Corporation

Input file dsdt.dat, Length 0x6FA5 (28581) bytes
ACPI: DSDT 0x0000000000000000 006FA5 (v01 LENOVO AMD 00001000 INTL 20120711)
Pass 1 parse of [DSDT]
Pass 2 parse of [DSDT]
Parsing Deferred Opcodes (Methods/Buffers/Packages/Regions)

Parsing completed

Found 6 external control methods, reparsing with new information
Pass 1 parse of [DSDT]
Pass 2 parse of [DSDT]
Parsing Deferred Opcodes (Methods/Buffers/Packages/Regions)

Parsing completed
Disassembly completed
ASL Output: dsdt.dsl - 318645 bytes

 iASL Warning: There were 6 external control methods found during
 disassembly, but only 0 were resolved (6 unresolved). Additional
 ACPI tables may be required to properly disassemble the code. This
 resulting disassembler output file may not compile because the
 disassembler did not know how many arguments to assign to the
 unresolved methods. Note: SSDTs can be dynamically loaded at
 runtime and may or may not be available via the host OS.

 To specify the tables needed to resolve external control method
 references, the -e option can be used to specify the filenames.
 Example iASL invocations:
     iasl -e ssdt1.aml ssdt2.aml ssdt3.aml -d dsdt.aml
     iasl -e dsdt.aml ssdt2.aml -d ssdt1.aml
     iasl -e ssdt*.aml -d dsdt.aml

 In addition, the -fe option can be used to specify a file containing
 control method external declarations with the associated method
 argument counts. Each line of the file must be of the form:
     External (<method pathname>, MethodObj, <argument count>)
 Invocation:
     iasl -fe refs.txt -d dsdt.aml

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.15.0-76-generic 4.15.0-76.86
ProcVersionSignature: Ubuntu 4.15.0-76.86-generic 4.15.18
Uname: Linux 4.15.0-76-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.9
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: eli 1603 F.... pulseaudio
 /dev/snd/controlC0: eli 1603 F.... pulseaudio
CurrentDesktop: ubuntu:GNOME
Date: Sat Feb 15 01:51:30 2020
InstallationDate: Installed on 2020-01-30 (15 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
MachineType: LENOVO 81LY
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB: 0 EFI VGA
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-76-generic root=UUID=97a5f239-2442-42e1-a2c8-b7bf4985a13a ro quiet splash vt.handoff=1
RelatedPackageVersions:
 linux-restricted-modules-4.15.0-76-generic N/A
 linux-backports-modules-4.15.0-76-generic N/A
 linux-firmware 1.173.14
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/28/2019
dmi.bios.vendor: LENOVO
dmi.bios.version: ARCN33WW
dmi.board.asset.tag: No Asset Tag
dmi.board.name: LNVNB161216
dmi.board.vendor: LENOVO
dmi.board.version: SDK0J40700WIN
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Lenovo IdeaPad L340-17API
dmi.modalias: dmi:bvnLENOVO:bvrARCN33WW:bd10/28/2019:svnLENOVO:pn81LY:pvrLenovoIdeaPadL340-17API:rvnLENOVO:rnLNVNB161216:rvrSDK0J40700WIN:cvnLENOVO:ct10:cvrLenovoIdeaPadL340-17API:
dmi.product.family: IdeaPad L340-17API
dmi.product.name: 81LY
dmi.product.version: Lenovo IdeaPad L340-17API
dmi.sys.vendor: LENOVO

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

This change was made by a bot.

[AaronMa (mapengyu)]

Could you try:

acpi_backlight=video

in kernel cmdline?

[Elijah Rockers (elijah-rockers)]

No change. /sys/class/backlist has acpi_video0 listed.

keyboard backlight controls do modify 'brightness' file, but there is no change to the backlight.

[Elijah Rockers (elijah-rockers)]

This problem is devastating my battery life, since my screen is at 100% brightness at all times .... if anyone has any ideas about how to fix this I'm all ears

[Kai-Heng Feng (kaihengfeng)]

Does this issue still happen under 20.04?

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]

[Julio Neto (julio-netu)]

This problem seems to persist on Ubuntu 20.10. The workaround is using an "external" app.
> sudo apt install brightness-controller

Probably this a nvidia related issue. Opening the Nvidia configuration app resets to max brightness.

[enygmata (heuripedes)]

This still happens in 20.04 with Ideapad L340 81TR0003BR.

The fix in my case is switching to to linux-oem-20.04b (linux-oem-20.04-edge should also work) and creating a Xorg configuration file that enables EnableBrightnessControl solved the issue, here's the full command:

cat <<EOF | sudo tee /usr/share/X11/xorg.conf.d/80-nvidia.conf
Section "Device"
    Identifier "Device0"
    Driver "nvidia"
    VendorName "NVIDIA Corporation"
    Option "RegistryDwords" "EnableBrightnessControl=1"
EndSection
EOF

nvidia.EnableBrightnessControl=1 on the kernel command line did not work for me.