Backlight brightness buttons not working on lenovo T420

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Backlight brightness buttons not working on lenovo T420

Postby minifrindge » 2017-03-26 14:32

My brightness control buttons are not working on my lenovo T420.

This laptop is configured with an integrated and a dedicated graphics card (Nvidia Quadro).

I use just the dedicated graphics card and I've disabled Optimus OS detection from BIOS.

I get this odd message on my kernel logs:
Code: Select all
sudo dmesg | grep thinkpad
[    3.898378] thinkpad_acpi: ThinkPad ACPI Extras v0.25
[    3.898380] thinkpad_acpi: http://ibm-acpi.sf.net/
[    3.898381] thinkpad_acpi: ThinkPad BIOS 83ET78WW (1.48 ), EC unknown
[    3.898382] thinkpad_acpi: Lenovo ThinkPad T420, model 4178A2G
[    3.899763] thinkpad_acpi: radio switch found; radios are enabled
[    3.899788] thinkpad_acpi: This ThinkPad has standard ACPI backlight brightness control, supported by the ACPI video driver
[    3.899789] thinkpad_acpi: Disabling thinkpad-acpi brightness events by default...
[    3.902921] thinkpad_acpi: Standard ACPI backlight interface available, not loading native one
[    3.906025] input: ThinkPad Extra Buttons as /devices/platform/thinkpad_acpi/input/input9


These messages concerning brightness go away by blacklisting acpi_backlight module. But when I blacklist the module I can not control the brightness whatsoever.

The /sys/class/backlight/ subsystem is not working and I can not change my screen brightness through Gnome slider or the Fn keys (home+end).

However xbacklight works fine.


Part of xorg.conf:
Code: Select all
Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "NVS 4200M"
    Option         "RegistryDwords" "EnableBrightnessControl=1"
EndSection


Fn keys are working ok
Code: Select all
$ acpi_listen
video/brightnessdown BRTDN 00000087 00000000
video/brightnessup BRTUP 00000086 00000000



I 've tried booting with many different parameters and tried every other solution I read online but none of that fixed it.

How can I fix this issue to work seamlessly just like it worked with the intel graphics card? I read somewhere that Optimus configurations may demonstrate this behavior but is there a solution?
Last edited by minifrindge on 2017-03-26 16:07, edited 2 times in total.
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Re: Brightness control buttons not working on lenovo T420

Postby phenest » 2017-03-26 15:57

Both the nVidia driver and xrandr only change the brightness through software and not the actual backlight.

If blacklisting the module stopped it working, then enable it again. And don't worry about the log message.

If it ain't broke, don't fix it.
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Re: Brightness control buttons not working on lenovo T420

Postby minifrindge » 2017-03-26 16:06

You are right about the xrandr brightness.

My main problem is that gnome can not control the backlight of my screen with the hotkeys or the brightness slider and not the log messages. Maybe these messages are a sign of a conflict.
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Re: Backlight brightness buttons not working on lenovo T420

Postby stevepusser » 2017-03-26 17:49

I don't see anything wrong with the log messages--they are just letting you know that the kernel found brightness control available in the laptop's firmware, and is not going to use an alternate kernel method. That's just information--not a warning of anything going wrong.
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Re: Backlight brightness buttons not working on lenovo T420

Postby phenest » 2017-03-26 19:48

There are plenty of recent posts about lcd backlights. Try adding:
Code: Select all
acpi_backlight=video

to the kernel boot line in grub. Worked for me.
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Re: Backlight brightness buttons not working on lenovo T420

Postby minifrindge » 2017-03-27 16:16

phenest wrote:There are plenty of recent posts about lcd backlights. Try adding:
Code: Select all
acpi_backlight=video

to the kernel boot line in grub. Worked for me.



I have try this and every kernel parameter solution.

I believe that this is an X server or gnome issue because if I do
Code: Select all
$ xbacklight -set 20


my screen dims seamlessly.

But my buttons and GNOME slider are not working.
When I press the brightness hotkeys the indicator pops up and I can change the levels but nothing else happens.
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Re: Backlight brightness buttons not working on lenovo T420

Postby phenest » 2017-03-27 18:04

minifrindge wrote:
phenest wrote:There are plenty of recent posts about lcd backlights. Try adding:
Code: Select all
acpi_backlight=video

to the kernel boot line in grub. Worked for me.


I have try this and every kernel parameter solution.

I doubt that. If "video" didn't work then try "vendor".
Code: Select all
acpi_backlight=vendor


minifrindge wrote:I believe that this is an X server or gnome issue because if I do
Code: Select all
$ xbacklight -set 20


my screen dims seamlessly.

The xserver and Gnome can only change brightness using software. And xbacklight may be using xrandr.
minifrindge wrote:But my buttons and GNOME slider are not working.
When I press the brightness hotkeys the indicator pops up and I can change the levels but nothing else happens.

This is because the hardware backlight needs to be enabled via the kernel.
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Re: Backlight brightness buttons not working on lenovo T420

Postby minifrindge » 2017-03-28 06:16

Code: Select all
acpi_backlight=vendor

This parameter makes my hotkey screen indicator unchangeable. The brightness does not change. xbacklight still works.
This could work but given the kernel thinkpad_acpi messages I mentioned in my initial post I believe it is a race condition between acpi and thinkpad_acpi modules .
Code: Select all
$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.9.0-2-amd64 root=UUID=b5342255-b92b-468e-abe0-4c1276ec373a ro acpi_backlight=vendor

In my /sys/class/backlight there is a thinkpad_screen folder
Code: Select all
/sys/class/backlight/thinkpad_screen $ ls
actual_brightness  bl_power  brightness  max_brightness  power  subsystem  type  uevent


Code: Select all
acpi_backlight=video

this keeps the subsystem exactly the same as it was with no acpi_backlight parameter.
Code: Select all
~ $ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.9.0-2-amd64 root=UUID=b5342255-b92b-468e-abe0-4c1276ec373a ro acpi_backlight=video
$ ls /sys/class/backlight/acpi_video0/
actual_brightness  bl_power  brightness  device  max_brightness  power  subsystem  type  uevent


So no, these kernel parameters do not bind a brightness event in my Gnome shell. Do you have any other idea what might be causing this problem?
Maybe this is a bug but I am not sure.

I forgot to mention that my system runs Debian testing (Stretch).

Code: Select all
$ uname -a
Linux t420 4.9.0-2-amd64 #1 SMP Debian 4.9.13-1 (2017-02-27) x86_64 GNU/Linux
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Re: Backlight brightness buttons not working on lenovo T420

Postby phenest » 2017-03-28 18:01

minifrindge wrote:My brightness control buttons are not working on my lenovo T420.

I get this odd message on my kernel logs:
Code: Select all
sudo dmesg | grep thinkpad
[    3.899789] thinkpad_acpi: Disabling thinkpad-acpi brightness events by default...
[    3.902921] thinkpad_acpi: Standard ACPI backlight interface available, not loading native one


These messages concerning brightness go away by blacklisting acpi_backlight module. But when I blacklist the module I can not control the brightness whatsoever.

phenest wrote:If blacklisting the module stopped it working, then enable it again. And don't worry about the log message.

So, the module is blacklisted? Did it work before you blacklisted it?
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Re: Backlight brightness buttons not working on lenovo T420

Postby minifrindge » 2017-03-29 14:22

phenest wrote:
minifrindge wrote:My brightness control buttons are not working on my lenovo T420.

I get this odd message on my kernel logs:
Code: Select all
sudo dmesg | grep thinkpad
[    3.899789] thinkpad_acpi: Disabling thinkpad-acpi brightness events by default...
[    3.902921] thinkpad_acpi: Standard ACPI backlight interface available, not loading native one


These messages concerning brightness go away by blacklisting acpi_backlight module. But when I blacklist the module I can not control the brightness whatsoever.

phenest wrote:If blacklisting the module stopped it working, then enable it again. And don't worry about the log message.

So, the module is blacklisted? Did it work before you blacklisted it?


I blacklisted acpi_backlight to see if thinkpad_acpi will take over control to have a working backlight control. But that did not happened. Instead my backlight was unchangeable even with the xbacklight utility that previously worked. However thinkpad-acpi stopped complaining in the kernel log about acpi backlight.
Now it is not blacklisted because I need working backlight even if the hotkeys are not working.
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Re: Backlight brightness buttons not working on lenovo T420

Postby vlitzer » 2017-04-08 19:14

I have the same issue, but with a different thinkpad (P50).
By default, noveau seemed to be working perfectly, but when I switched to the nvidia drivers, it stopped.
xbacklight command works, and I tried every suggestion in this thread, to no avail (including the xorg nvidia section, and the grub parameters)
Also /sys/class/backlight/ has nothing on it.
Any suggestions / guidance will be appreciated.
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Re: Backlight brightness buttons not working on lenovo T420

Postby stevepusser » 2017-04-08 22:26

You should start a new thread about your particular laptop, and not hijack one about different hardware.

Also, some information about the hardware in your machine is probably very useful. A simple method is to install inxi and give us the results of "inxi -F" in a code box.
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Re: Backlight brightness buttons not working on lenovo T420

Postby minifrindge » 2017-04-09 07:57

stevepusser wrote:Also, some information about the hardware in your machine is probably very useful. A simple method is to install inxi and give us the results of "inxi -F" in a code box.


Code: Select all
$ inxi -F
System:    Host: t420 Kernel: 4.9.0-2-amd64 x86_64 (64 bit) Desktop: Gnome 3.22.3
           Distro: Debian GNU/Linux 9 (stretch)
Machine:   Device: laptop System: LENOVO product: 4178A2G v: ThinkPad T420
           Mobo: LENOVO model: 4178A2G UEFI [Legacy]: LENOVO v: 83ET78WW (1.48 ) date: 01/21/2016
Battery    BAT0: charge: 38.3 Wh 99.5% condition: 38.5/47.5 Wh (81%)
CPU:       Dual core Intel Core i5-2410M (-HT-MCP-) cache: 3072 KB
           clock speeds: max: 2900 MHz 1: 800 MHz 2: 804 MHz 3: 840 MHz 4: 890 MHz
Graphics:  Card: NVIDIA GF119M [Quadro NVS 4200M]
           Display Server: X.Org 1.19.2 driver: nvidia Resolution: 1366x768@60.10hz, 1920x1080@60.00hz
           GLX Renderer: NVS 4200M/PCIe/SSE2 GLX Version: 4.5.0 NVIDIA 375.39
Audio:     Card-1 NVIDIA GF119 HDMI Audio Controller driver: snd_hda_intel Sound: ALSA v: k4.9.0-2-amd64
           Card-2 Intel 6 Series/C200 Series Family High Definition Audio Controller driver: snd_hda_intel
Network:   Card-1: Intel 82579LM Gigabit Network Connection driver: e1000e
           IF: eth0 state: up speed: 100 Mbps duplex: full mac: <>
           Card-2: Intel Centrino Advanced-N 6205 [Taylor Peak] driver: iwlwifi
           IF: wlan0 state: up mac: <>
Drives:    HDD Total Size: 120.0GB (42.2% used)
           ID-1: /dev/sda model: INTEL_SSDSC2BW12 size: 120.0GB
Partition: ID-1: / size: 32G used: 17G (54%) fs: ext4 dev: /dev/sda1
           ID-2: /home size: 74G used: 27G (38%) fs: ext4 dev: /dev/sda6
           ID-3: swap-1 size: 5.00GB used: 0.00GB (0%) fs: swap dev: /dev/sda5
Sensors:   System Temperatures: cpu: 65.0C mobo: N/A gpu: 72C
           Fan Speeds (in rpm): cpu: 3536
Info:      Processes: 261 Uptime: 2 min Memory: 2204.5/7940.9MB Client: Shell (bash) inxi: 2.3.5


My laptop also features an integrated graphics.
My bios settings is set to use discrete graphics and nvidia Optimus OS detection is disabled.
If I do something else my boot process blocks (is it because I have blacklisted nouveau).
I sense that intel_backlight needs to be loaded.

Here https://wiki.archlinux.org/index.php/backlight#Kernel_command-line_options refers that this is an issue with Nvidia Optimus laptops like this one.


vlitzer wrote:I have the same issue, but with a different thinkpad (P50).
By default, noveau seemed to be working perfectly, but when I switched to the nvidia drivers, it stopped.
xbacklight command works, and I tried every suggestion in this thread, to no avail (including the xorg nvidia section, and the grub parameters)
Also /sys/class/backlight/ has nothing on it.
Any suggestions / guidance will be appreciated.


Does your laptop also have an nvidia Optimus?
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Re: Backlight brightness buttons not working on lenovo T420

Postby vlitzer » 2017-04-09 15:02

it was not my intention to hijack the thread. I think I have the same issue and I am posting to see if minifrindge gets it solved. Happy to create a different thread.
I do have optimus, and I also had to disable the hybrid graphics since my X session was crashing after I got nvidia video card installed.
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