Keyboard backlight doesn't work on Samsung laptop

rdflores · Post by **rdflores** » Sun Jun 13, 2021 7:09 pm

Hi.
The keyboard backlight control (Fn+F9) doesn't work on Mint, but it works on Windows 10 (both OS installed on my Samsung laptop). Does anyone know how to fix this? Or at least help me keep the keyboard backlight always on?
PS: the Fn+F2/F3 works fine to control the screen brightness. Fn+F7/F8 works fine to control the volume too.

When the keyboard backlight is ON (because I turned it on from Windows) I see:

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xxd -p /sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
0700000003

But when it is OFF I see:

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xxd -p /sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
0700000000

I was able to write 0700000003 to KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852 but nothing happened. And after rebooting the laptop the value returned to 0700000000.

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lsattr /sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
chattr -i /sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
lsattr /sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
echo 0700000003 | xxd -p -r > /sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
chattr +i /sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
xxd -p /sys/firmware/efi/efivars/KBDBacklitLvl-5af56f53-985c-47d5-920c-f1c531d06852
0700000003

More info about my laptop:

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inxi -Fxxxza
System:    Kernel: 5.4.0-74-generic x86_64 bits: 64 compiler: gcc v: 9.3.0 
           parameters: BOOT_IMAGE=/boot/vmlinuz-5.4.0-74-generic root=UUID=c37c02ce-9aee-42e9-975c-460560e9a166 ro quiet splash 
           Desktop: Cinnamon 4.6.7 wm: muffin 4.6.3 dm: LightDM 1.30.0 Distro: Linux Mint 20 Ulyana base: Ubuntu 20.04 focal 
Machine:   Type: Laptop System: SAMSUNG product: 750XBE/730XBE v: P03REY serial: <filter> Chassis: type: 10 serial: <filter> 
           Mobo: SAMSUNG model: NP730XBE-KP1BR v: SGLA207A06-C01-G002-S0001+10.0.18362 serial: <filter> 
           UEFI: American Megatrends v: P03REY.055.200422.ZW date: 04/22/2020 
Battery:   ID-1: BAT1 charge: 34.9 Wh condition: 52.9/55.2 Wh (96%) volts: 11.7/11.5 
           model: SAMSUNG Electronics SR Real Battery type: Li-ion serial: <filter> status: Discharging cycles: 63 
CPU:       Topology: Dual Core model: Intel Core i3-8145U bits: 64 type: MT MCP arch: Kaby Lake family: 6 model-id: 8E (142) 
           stepping: B (11) microcode: EA L1 cache: 128 KiB L2 cache: 4096 KiB L3 cache: 4096 KiB 
           flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 18399 
           Speed: 754 MHz min/max: 400/3900 MHz Core speeds (MHz): 1: 700 2: 700 3: 700 4: 700 
           Vulnerabilities: Type: itlb_multihit status: KVM: Split huge pages 
           Type: l1tf status: Not affected 
           Type: mds mitigation: Clear CPU buffers; SMT vulnerable 
           Type: meltdown status: Not affected 
           Type: spec_store_bypass mitigation: Speculative Store Bypass disabled via prctl and seccomp 
           Type: spectre_v1 mitigation: usercopy/swapgs barriers and __user pointer sanitization 
           Type: spectre_v2 mitigation: Full generic retpoline, IBPB: conditional, IBRS_FW, STIBP: conditional, RSB filling 
           Type: srbds mitigation: Microcode 
           Type: tsx_async_abort status: Not affected 
Graphics:  Device-1: Intel UHD Graphics 620 vendor: Samsung Co driver: i915 v: kernel bus ID: 00:02.0 chip ID: 8086:3ea0 
           Display: server: X.Org 1.20.9 driver: modesetting unloaded: fbdev,vesa resolution: 1600x900~60Hz 
           OpenGL: renderer: Mesa Intel UHD Graphics 620 (WHL GT2) v: 4.6 Mesa 20.2.6 direct render: Yes 
Audio:     Device-1: Intel Cannon Point-LP High Definition Audio vendor: Samsung Co driver: snd_hda_intel v: kernel 
           bus ID: 00:1f.3 chip ID: 8086:9dc8 
           Sound Server: ALSA v: k5.4.0-74-generic 
Network:   Device-1: Intel Cannon Point-LP CNVi [Wireless-AC] driver: iwlwifi v: kernel port: 3000 bus ID: 00:14.3 
           chip ID: 8086:9df0 
           IF: wlo1 state: up mac: <filter> 
Drives:    Local Storage: total: 238.47 GiB used: 84.15 GiB (35.3%) 
           SMART Message: Required tool smartctl not installed. Check --recommends 
           ID-1: /dev/sda vendor: LITE-ON model: CV8-8E256 size: 238.47 GiB block size: physical: 512 B logical: 512 B 
           speed: 6.0 Gb/s serial: <filter> rev: 002 scheme: GPT 
RAID:      Hardware-1: Intel 82801 Mobile SATA Controller [RAID mode] driver: ahci v: 3.0 port: 3060 bus ID: 00:17.0 
           chip ID: 8086.282a rev: 11 
Partition: ID-1: / raw size: 22.35 GiB size: 21.88 GiB (97.87%) used: 15.08 GiB (68.9%) fs: ext4 block size: 4096 B 
           dev: /dev/sda7 
           ID-2: /home raw size: 98.05 GiB size: 96.01 GiB (97.92%) used: 69.01 GiB (71.9%) fs: ext4 block size: 4096 B 
           dev: /dev/sda9 
           ID-3: swap-1 size: 3.82 GiB used: 13.0 MiB (0.3%) fs: swap swappiness: 60 (default) cache pressure: 100 (default) 
           dev: /dev/sda8 
Sensors:   System Temperatures: cpu: 46.0 C mobo: 46.0 C 
           Fan Speeds (RPM): N/A 
Info:      Processes: 243 Uptime: 40m Memory: 3.74 GiB used: 2.34 GiB (62.7%) Init: systemd v: 245 runlevel: 5 Compilers: 
           gcc: 9.3.0 alt: 9 Shell: bash (sudo) v: 5.0.17 running in: gnome-terminal inxi: 3.0.38

Thanks.