I've spent many hours trying to find a solution but nothing seems to work. I've successfully installed Ubuntu 18.04 on Lenovo G505S laptop in UEFI mode with just nomodeset flag added to grub. Everything seems to work but except screen brightness which is always at 100%. Here's what I've found out until now:

  • No matter what I do screen is always at its maximum brightness
  • I either have acpi_video0 and acpi_video1 or ideapad in /sys/class/backlight depending on acpi_backlight grub option
  • Changing brightness with keys changes "brightness" file in acpi_video0 or ideapad
  • Changing brightness with keys shows BRTUP and BRTDN on acpi_listen
  • Laptop has two amd cards, but changing bios settings from switchable to integrated doesn't help
  • Grub options doesn't make much difference, except making the system unable to start from time to time. The ones I tried are: acpi_osi acpi_backlight radeon.modeset and some more
  • I've tried making changes to /usr/share/X11/xorg.conf.d by changing existing files (10-radeon.conf 10-amdgpu.conf) and adding 80-backlight.conf but that doesn't help either. Most of the info on the web seems to be for intel cards so this one was just a guess.
  • xbacklight, setpci, gdbus and external programs also can't change brightness
  • blacklisting ideapad_laptop doesn't help
  • updating kernel did nothing (I've tried 4.19 and 4.17)
  • not sure if connected but system seems to have problems waking up from hibernation

Any help will be greatly appreciated and will help me retain my sanity.

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