Brightness hotkeys not working on Lenovo S740

Bug #1872311 reported by Elias Julkunen
This bug affects 9 people
Affects Status Importance Assigned to Milestone
linux (Ubuntu)

Bug Description

Brightness hotkeys (Fn + F11 for decrease and Fn + F12 for increase) do not work on Ubuntu 20.04 and Lenovo S740 laptop. The brightness hotkeys did not work on 19.10 either.

I followed the guide here:

In "Step-by-step Troubleshooting", none of the steps (1-7) did produce any reaction to brightness change key combinations. However, I am able to change the laptop screen brightness through the brightness applet.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-21-generic 5.4.0-21.25
ProcVersionSignature: Ubuntu 5.4.0-21.25-generic 5.4.27
Uname: Linux 5.4.0-21-generic x86_64
ApportVersion: 2.20.11-0ubuntu26
Architecture: amd64
 /dev/snd/controlC1: elias 1447 F.... pulseaudio
 /dev/snd/controlC0: elias 1447 F.... pulseaudio
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Sun Apr 12 16:12:01 2020
InstallationDate: Installed on 2019-11-19 (144 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
MachineType: LENOVO 81RS
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-21-generic root=UUID=101c7da4-860d-4496-ae06-d98699795f9a ro quiet splash vt.handoff=7
 linux-restricted-modules-5.4.0-21-generic N/A
 linux-backports-modules-5.4.0-21-generic N/A
 linux-firmware 1.187
SourcePackage: linux
UpgradeStatus: Upgraded to focal on 2020-04-04 (7 days ago) 03/10/2020
dmi.bios.vendor: LENOVO
dmi.bios.version: BYCN33WW
dmi.board.asset.tag: NO Asset Tag LNVNB161216
dmi.board.vendor: LENOVO
dmi.board.version: SDK0J40709 WIN
dmi.chassis.asset.tag: NO Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Lenovo Yoga S740-14IIL
dmi.modalias: dmi:bvnLENOVO:bvrBYCN33WW:bd03/10/2020:svnLENOVO:pn81RS:pvrLenovoYogaS740-14IIL:rvnLENOVO:rnLNVNB161216:rvrSDK0J40709WIN:cvnLENOVO:ct10:cvrLenovoYogaS740-14IIL: Yoga S740-14IIL 81RS
dmi.product.sku: LENOVO_MT_81RS_BU_idea_FM_Yoga S740-14IIL
dmi.product.version: Lenovo Yoga S740-14IIL
dmi.sys.vendor: LENOVO

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Elias Julkunen (eliasj) wrote :
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Elias Julkunen (eliasj) wrote :
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Elias Julkunen (eliasj) wrote :
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Ubuntu Kernel Bot (ubuntu-kernel-bot) wrote : Status changed to Confirmed

This change was made by a bot.

Changed in linux (Ubuntu):
status: New → Confirmed
Revision history for this message
Alex Hung (alexhung) wrote :

The brightness interface (/sys/class/backlight/intel_backlight) is working, so it must be the missing events that cause your problem.

Ubuntu needs keycodes (KEY_BRIGHTNESSDOWN 224 & KEY_BRIGHTNESSUP 225), and this can be from either scancode or ACPI events. Laptops usually use ACPI for brightness, and this can be confirmed by pressing hotkeys while running

   $ watch -n1 cat /proc/interrupts

Note: ACPI usually is on IRQ 9. Check whether interrupts increase with brightness up/down presses.

Revision history for this message
Alex Hung (alexhung) wrote :

If ACPI approach is used, there are also two different approaches used - ACPI standard or OEM-specific .

ACPI defines events from brightness up and down, and it is video/brightnessdown BRTDN 00000087 & video/brightnessup BRTUP 00000086. The can be checked by running "acpi_listen" and pressing brightness hotkeys.

If OEM-specific events are used, it should be handled by platform driver like "ideapad_laptop".

Would you mind sharing acpidump log (sudo acpidump > acpi.log) so more analysis can be performed?

Revision history for this message
Elias Julkunen (eliasj) wrote :

Thanks for the comments. Please find attached the requested file (sudo acpidump > acpi.log).

However, "watch -n1 cat /proc/interrupts" did not increase when I used the Fn + F10/F11 (brightness) button. Contrast to that, the (working) volume hotkeys increased the interrupts. I also ran "acpi_listen" and same thing - nothing when brightness hotkeys were pressed, and the correct input with volume hotkeys.

Revision history for this message
Alex Hung (alexhung) wrote :

No ACPI interrupts means either BIOS is broken or system is using other mechanism like scancode from KBC/EC.

Checking scancode is easy: sudo showkey -s
Also checking interrupts: watch -n1 cat /proc/interrupts <-- usually IRQ 1

If there aren't events from KBC/EC, this is a BIOS or a KBC/EC bug.

Revision history for this message
Elias Julkunen (eliasj) wrote :

Thanks, "sudo showkey -s" does not show anything for the brightness key combination. Neither do the interrupts increase when the brightness key combination is pressed. So I assume this cannot be fixed from the software side.

The brightness keys are working on Windows. However, the laptop is quite new so maybe the support just isn't there yet.

Revision history for this message
Alex Hung (alexhung) wrote :

It may worth a shot to ask on Lenovo's forum ( Perhaps they will forward this to developers who can take a look and release a fix for everybody.

Revision history for this message
Elias Julkunen (eliasj) wrote :

Hi, I posted about this here:

Let's hope someone picks up on this - so far no one has.

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Kai-Heng Feng (kaihengfeng) wrote :

Is the panel OLED?

Revision history for this message
Alexander Wong (udia) wrote :

I discovered this exact same issue, but with a slightly different environment.
Perhaps it's not an Ubuntu bug but an issue with the kernel?

The brightness keys work in Windows.
In linux, I can still adjust the brightness using the power manager slider despite the keyboard hotkeys not working.

I am using the Lenovo Yoga C740, with my primary OS as Debian Buster.
The brightness up and down keys (F11, F12) do not emit keycodes when pressed, even though holding down Fn and pressing F11 I am able to emit the function key behavior.
These issues persist when using Ubuntu 20.04 through a live usb.

I wrote a summary of my issues here:

Revision history for this message
Jaromir Obr (jaromir-obr) wrote :

I had similar issue with Lenovo Yoga Slim 7 AMD Ryzen 4700U, in Ubuntu 20.04.1.
Solved by upgrade of kernel to latest upstream (5.8). Another solution for me was installation of AMDGPU proprietary drivers.

Revision history for this message
Andrea Stevanato (thymbahutymba) wrote :

I have the same problem with the Lenovo S740. Brightness hotkeys not
working at all. I've tried several options as stated in
Using acpi_backlight=vendor totally break the backlight, it cannot be
changed even from the gnome panel.

Moreover, with showkey I've tested the hotkeys that are not working
which are:
F4: disable mic
F6: disable touchpad
F7: airplane mode
F8: disable camera
F11-F12: brightness

Revision history for this message
akash rayhan (akashrayhan) wrote :

Elias Julkunen. Did you find any solution? Currently i am facing the same problem. My hardware is Lenovo Ideapad-5-15ITL05. If you found the solution can you please share it with me?

Revision history for this message
Elias Julkunen (eliasj) wrote :

Hi, unfortunately not. Maybe it will get fixed sometime.

Revision history for this message
Kai-Heng Feng (kaihengfeng) wrote :

Please test latest drm-tip kernel:

Headers are not needed.

Changed in linux (Ubuntu):
status: Confirmed → Incomplete
Revision history for this message
Elias Julkunen (eliasj) wrote :

Thanks for the suggestion. However, this does not make any difference. I ran also "watch -n1 cat /proc/interrupts", "acpi_listen" and "sudo showkey -s" and no reaction to brightness hotkeys whereas volume hotkeys work and that also shows up when running these commands.

Revision history for this message
Launchpad Janitor (janitor) wrote :

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

Changed in linux (Ubuntu):
status: Incomplete → Expired
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