Debian 9: Backlight Brightness

5,767

Solution 1

Your system seems to have two interfaces for backlight control: backlight:acpi_video0 and backlight:radeon_bl0. And apparently the ACPI interface does not work, and/or causes problems when used together with the Radeon-specific interface.

Since the Radeon-specific interface seems to work fine, I'd try telling systemd to stop using the ACPI backlight interface first:

systemctl mask systemd-backlight@backlight:acpi_video0.service

If necessary, this can be undone with:

systemctl unmask systemd-backlight@backlight:acpi_video0.service

If this does not help, further investigation is needed.

With journalctl -xb you should be able to see a quite verbose version of messages for the current boot only. By default, persistent storage of systemd journal is not enabled in Debian 9, but it's quite easy to enable: just run mkdir /var/log/journal as root. Then, starting from next boot, the journal will be stored persistently and you will be able to e.g. view the log of the previous boot from startup to shutdown with journalctl -xb -1. The oldest logs will eventually be automatically purged, controlled by journald's configurable criteria for available disk space.

Solution 2

Open file /etc/default/grub and update the line:

GRUB_CMDLINE_LINUX_DEFAULT="quiet"

To line:

GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_backlight=video"

Then run:

update-grub
reboot

Possible alternative parameters case this one doesn't work (complete discussion at Kernel command-line options):

acpi_backlight=video
acpi_backlight=vendor
acpi_backlight=native
acpi_backlight=none

In my case, acpi_backlight=video seems to have solved both issues:

  • backlight brightness is no longer resetting to max during boot (question 1)
  • [Fn] + ←/→ was set as shortcut for decrease/increase backlight brightness (question 2)

After that there was a conflict with the shortcut [Fn] + ←, which was decreasing the backlight brightness but also opening the Display Settings window. Just opened Preferences > Setup Hot Keys and changed the 'obscure' Hotkey XF86Display to something else.

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Mark Messa
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Mark Messa

I have no special talent. I am only passionately curious.

Updated on September 18, 2022

Comments

  • Mark Messa
    Mark Messa over 1 year

    I've just installed a fresh new Debian 9 with LXDE into an ACER AMD Notebook and everything seems to be working fine, except for the backlight brightness. During the boot, it happens the following:

    • several messages and errors appear

      [FAILED] Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0.
      See 'systemctl status systemd-backlight@backlight:acpi_video0.service' for details.
      Starting Load/Save Screen Backlight Brightness of backlight:radeon_bl0
      ...
      [ OK ] Started Load/Save Screen Backlight Brightness of backlight:radeon_bl0
      
    • often backlight brightness is reset to max

    In order to set the backlight brightness to an acceptable level, the best solution so far seems to be opening a terminal and typing the command line below as soon as Debian initialize:

    • tee /sys/class/backlight/radeon_bl0/brightness <<< 15

     

    Questions

    1. How to avoid the backlight brightness being reset to max during the boot?
    2. How to set shortcuts to the backlight brightness (ex: [Fn] + ←/→)?

     


    Debug

    root@debian:~# dmesg | grep -i "error\|firmware\|backlight"
    [    1.049855] pci 0000:01:00.0: [Firmware Bug]: disabling VPD access (can't determine size of non-standard VPD format)
    [    7.729996] EXT4-fs (sda1): re-mounted. Opts: errors=remount-ro
    [   12.960474] radeon 0000:00:01.0: firmware: direct-loading firmware radeon/PALM_pfp.bin
    [   13.017938] radeon 0000:00:01.0: firmware: direct-loading firmware radeon/PALM_me.bin
    [   13.043827] radeon 0000:00:01.0: firmware: direct-loading firmware radeon/SUMO_rlc.bin
    [   13.161157] radeon 0000:00:01.0: firmware: direct-loading firmware radeon/SUMO_uvd.bin
    [   13.897112] [drm] radeon atom DIG backlight initialized
    

     

    root@debian:~# systemctl status systemd-backlight@backlight:acpi_video0.service
    ● systemd-backlight@backlight:acpi_video0.service - Load/Save Screen Backlight Brightness of backlight:acpi_video0
       Loaded: loaded (/lib/systemd/system/[email protected]; static; vendor preset: enabled)
       Active: failed (Result: exit-code) since Sat 2018-06-16 06:37:19 -03; 29min ago
         Docs: man:[email protected](8)
      Process: 411 ExecStart=/lib/systemd/systemd-backlight load backlight:acpi_video0 (code=exited, status=1/FAILURE)
     Main PID: 411 (code=exited, status=1/FAILURE)
    
    Jun 16 06:37:19 debian systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:acpi_video0...
    Jun 16 06:37:19 debian systemd[1]: systemd-backlight@backlight:acpi_video0.service: Main process exited, code=exited, status=1/FAILURE
    Jun 16 06:37:19 debian systemd[1]: Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video0.
    Jun 16 06:37:19 debian systemd[1]: systemd-backlight@backlight:acpi_video0.service: Unit entered failed state.
    Jun 16 06:37:19 debian systemd[1]: systemd-backlight@backlight:acpi_video0.service: Failed with result 'exit-code'.
    

    Hardware Specifications
    Notebook Aspire E1-421-0622 | product details

    • AMD 2 Core™ Processor E1-1200 (1.4 GHz) 1MB Cache 64-bit Processing
    • AMD Radeon HD 7310 Graphics Controller
    • 2Gb DDR3 SDRAM Memory
    • 256MB shared video memory

     

    Debian Strech
    debian-9.4.0-amd64-netinst.iso

    • Small CDs
    • AMD64 processor architecture
    • Non-free package firmware-amd-graphics installed
      radeon kernel modesetting for R600 or later requires firmware-amd-graphics
    • Software selection
      (  ) Debian desktop environment
      (  ) ... GNOME
      (  ) ... Xfce
      (  ) ... KDE
      (  ) ... Cinnamon
      (  ) ... MATE
      (X) ... LXDE
      (  ) web server
      (X) print server
      (  ) SSH server
      (X) standard system utilities
  • Mark Messa
    Mark Messa almost 6 years
    I've also posted a partial solution. Let me know your comments.
  • Mark Messa
    Mark Messa almost 6 years
    Just tested journalctl -xb and, indeed, there is a lot of verbose in it. However, it is not in a 'friendly' manner compared to messages and errors. It seems awkward to me having to take a picture of the screen in order to capture the messages and errors during boot.
  • Ombrophile
    Ombrophile almost 4 years
    It is good if setting acpi_backlight=video worked, but this option means that acpi will use its default driver, ie, video.ko [Ref.: kernel.org/doc/Documentation/admin-guide/kernel-parameters.t‌​xt]. As @telecoM rightly said, having both acpi_video0 and radeon_bl0 in /sys/class/backlight means that there are two interfaces for backlight control and one needs to be turned off. Since I too was facing the same issue, I went on with acpi_backlight=native option to let only radeon control backlight. And sure enough the brightness reset issue was gone.