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mpboden
Asked: 2024-02-27 12:47:40 +0800 CST

Why is my laptop screen dim after resume from screen-lock, sleep, or suspend?

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After every resume from screen-lock, sleep, or suspend, my laptop screen is very dim. If I type Fn+F6, then the screen jumps to 100% brightness instantly. (F5 and F6 are my brightness control keys.)

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.6 LTS
Release:    20.04
Codename:   focal

$ lspci -nnk | grep -EA3 VGA
01:00.0 VGA compatible controller [0300]: NVIDIA Corporation Device [10de:25b8] (rev a1)
    Subsystem: Lenovo Device [17aa:22d8]
    Kernel driver in use: nouveau
    Kernel modules: nvidiafb, nouveau

$ sudo lshw -c video
  *-display                 
       description: VGA compatible controller
       product: NVIDIA Corporation
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       logical name: /dev/fb0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom fb
       configuration: depth=32 driver=nouveau latency=0 mode=1920x1080 visual=truecolor xres=1920 yres=1080
       resources: iomemory:400-3ff iomemory:410-40f irq:199 memory:ab000000-abffffff memory:4000000000-40ffffffff memory:4100000000-4101ffffff ioport:3000(size=128) memory:ac080000-ac0fffff

$ sudo lshw | grep -i lenovo
    product: 20YU002HUS (LENOVO_MT_20YU_BU_Think_FM_ThinkPad P17 Gen 2i)
    vendor: LENOVO
    configuration: administrator_password=disabled chassis=notebook family=ThinkPad P17 Gen 2i power-on_password=disabled sku=LENOVO_MT_20YU_BU_Think_FM_ThinkPad P17 Gen 2i uuid=4C043C28-3F2B-B211-A85C-940FFC06910B
       vendor: LENOVO
          vendor: LENOVO

Before screen-lock, sleep, or suspend:

$ cat /sys/class/backlight/nv_backlight/actual_brightness 
100

Power Settings Before Brightness Setting Before

After screen-lock, sleep, or suspend:

$ cat /sys/class/backlight/nv_backlight/actual_brightness 
33

Power Settings After Brightness Setting After

I'm entering lock mode by any of the following:

  • By inactivity
  • From command line with: xdg-screensaver lock
  • From drop-down menu by clicking: Lock

I'm entering sleep/suspend mode by any of the following:

  • From command line with: systemctl suspend
  • From drop-down menu by clicking: Power Off/Log Out > Suspend

Take note that after resume from lock/sleep/suspend, the content of /sys/class/backlight/nv_backlight/actual_brightness is 33, not 100.

To achieve full brightness again, I only have to type Fn+F6 once. I find this a bit odd, because typically, if the brightness is that low, it would take several key presses. For example, to go from 30 to 100, it would normally be seven key presses.

Also, you'll notice in the Settings/Power window that the brightness level indicates it's at 100%, both before and after lock/sleep/suspend.

Finally, you'll notice that I have the setting, Dim Screen When Inactive, disabled.

In my attempt to come up with some sort of solution, I installed xbacklight with the idea that I could use it in a script to automatically reset my brightness. But this had no affect.

I also attempted the following commands, but the brightness levels don't change, and I'm unable to write to the file. Perhaps this is the wrong approach.

$ sudo chmod 644 /sys/class/backlight/nv_backlight/actual_brightness

$ sudo tee /sys/class/backlight/nv_backlight/actual_brightness <<< 100
100
tee: /sys/class/backlight/nv_backlight/actual_brightness: Input/output error

$ sudo su

# echo 100 > /sys/class/backlight/nv_backlight/actual_brightness
bash: echo: write error: Input/output error

Why is this symptom happening, and how do I fix it? Ideally, I would prefer to not incorporate a script that runs at login. This seems like treating the symptom and not the cause.

UPDATE

I attempted the two following suggested solutions, but neither worked.

Suggestion 1 - Systemd service

  • Create file:

     $ cat /etc/systemd/system/nvidia-backlight-sleep

 [Unit]
 Description=Fix Nvidia backlight after suspend
 Before=sleep.target
 StopWhenUnneeded=yes

 [Service]
 Type=oneshot
 RemainAfterExit=yes
 ExecStart=/bin/bash -c "cat /sys/class/backlight/nv_backlight/actual_brightness > /run/previous_nv_backlight_brightness"
 ExecStop=/bin/bash -c "sleep 1; cat /run/previous_nv_backlight_brightness > /sys/class/backlight/nv_backlight/brightness"

 [Install]
 WantedBy=sleep.target

  • Reload systemd daemons: sudo systemctl daemon-reload

  • Enable service: sudo systemctl enable nvidia-backlight-sleep

Suggestion 2 - Create script in /lib/systemd/system-sleep

  • Create file:

     $ cat /lib/systemd/system-sleep/nvidia-backlight-sleep

 #!/bin/bash

 case $1 in
   post)
     sleep 1
     echo 50 > /sys/class/backlight/nv_backlight/brightness
     ;;
 esac

  • Make executable: sudo chmod 755 /lib/systemd/system-sleep/nvidia-backlight-sleep

nvidia

2 Answers

  1. Best Answer

    I was able to solve my problem by switching from the open-source nouveau driver to the proprietary nvidia-driver-535. This can be installed from either the command line or through the GUI. I chose to install it through the GUI.

    1. In Activities, search for “driver” and click on “Additional Drivers” icon. enter image description here
    2. The “Software & Updates” window will open to the "Additional Drivers" tab. enter image description here
    3. I selected "Using NVIDIA driver metapackage from nvidia-driver-535 (proprietary)" and clicked on "Apply Changes" enter image description here
    4. I rebooted computer

    After a reboot, you can see that the Nvidia driver is in use:

    $ sudo lshw -c video
  *-display                 
       description: VGA compatible controller
       product: NVIDIA Corporation
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: iomemory:400-3ff iomemory:410-40f irq:200 memory:ab000000-abffffff memory:4000000000-40ffffffff memory:4100000000-4101ffffff ioport:3000(size=128) memory:ac080000-ac0fffff

    Additionally, along with the installation of the driver, a utility called nvidia-settings is installed. Run that with sudo nvidia-settings and the following window displays: enter image description here

    Another utility app that is installed with the Nvidia driver is System Management Interface, nvidia-sma:

    $ nvidia-smi
Tue Feb 27 21:32:15 2024       
+---------------------------------------------------------------------------------------+
| NVIDIA-SMI 535.161.07             Driver Version: 535.161.07   CUDA Version: 12.2     |
|-----------------------------------------+----------------------+----------------------+
| GPU  Name                 Persistence-M | Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp   Perf          Pwr:Usage/Cap |         Memory-Usage | GPU-Util  Compute M. |
|                                         |                      |               MIG M. |
|=========================================+======================+======================|
|   0  NVIDIA RTX A2000 Laptop GPU    Off | 00000000:01:00.0  On |                  N/A |
| N/A   38C    P8               7W /  60W |    411MiB /  4096MiB |      1%      Default |
|                                         |                      |                  N/A |
+-----------------------------------------+----------------------+----------------------+
                                                                                         
+---------------------------------------------------------------------------------------+
| Processes:                                                                            |
|  GPU   GI   CI        PID   Type   Process name                            GPU Memory |
|        ID   ID                                                             Usage      |
|=======================================================================================|
|    0   N/A  N/A      1344      G   /usr/lib/xorg/Xorg                           39MiB |
|    0   N/A  N/A      2153      G   /usr/lib/xorg/Xorg                          114MiB |
|    0   N/A  N/A      2282      G   /usr/bin/gnome-shell                         83MiB |
|    0   N/A  N/A      7710      G   /usr/lib/firefox/firefox                    153MiB |
+---------------------------------------------------------------------------------------+

    Finally, I can lock or suspend my laptop and the screen backlight brightness settings are retained. Whereas before the value was saved in /sys/class/backlight/nv_backlight/actual_brightness, the new driver saves the value in /sys/class/backlight/nvidia_0/actual_brightness:

    $ cat /sys/class/backlight/nvidia_0/actual_brightness 
100

    In conclusion, I think that there's a bug with the nouveau driver that is incorrectly saving and recalling the actual_brightness value. For some reason, it always resumed from lock or sleep/suspend with a value of 33.

    • 1

  2. It seems like your Nvidia driver isn't remembering the backlight value even though your GNOME does. Let's work around this with a sleep hook:

    1. Paste the following into /etc/systemd/system/nvidia-backlight-sleep-askubuntu-1505827-1004020.service

      [Unit]
Description=Fix Nvidia backlight after suspend
Before=sleep.target
StopWhenUnneeded=yes

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/bash -c "cat /sys/class/backlight/nv_backlight/actual_brightness > /run/previous_nv_backlight_brightness"
ExecStop=/bin/bash -c "sleep 1; cat /run/previous_nv_backlight_brightness > /sys/class/backlight/nv_backlight/brightness"

[Install]
WantedBy=sleep.target

    2. Run sudo systemctl daemon-reload

    3. Run sudo systemctl enable nvidia-backlight-sleep-askubuntu-1505827-1004020.service

    actual_brightness isn't the writable one so we need to use the brightness file. You can also adjust the sleep 1 in case it doesn't work or if you want it to be restored quicker. /lib/systemd/system/[email protected] is responsible for saving at shutdown/startup while the GPU driver itself is responsible for suspend/resume.

    Alternative solution

    If that doesn't work, we can hardcode more things:

    1. Disable and remove the other solution

    2. Paste the following into /lib/systemd/system-sleep/nvidia-backlight-sleep-askubuntu-1505827-1004020

      #!/bin/bash

case $1 in
  post)
    sleep 1
    echo 50 > /sys/class/backlight/nv_backlight/brightness
    ;;
esac

    3. sudo chmod 755 /lib/systemd/system-sleep/nvidia-backlight-sleep-askubuntu-1505827-1004020

    • 0