Can you try each of the following kernel parameters, one at a time, and check:
- the number of backlight interfaces in /sys/class/backlight
- whether echoing any value in the brightness file for any of the interfaces affects brightness
Code:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""
Code:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX="acpi_backlight=vendor"
Code:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX="acpi_osi=Linux"
Code:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX="acpi_osi=Linux acpi_backlight=vendor"
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Can you also try the following methods to see if either changes the brightness:
Code:
sudo setpci -s 01:00.0 F4.B=7f
sudo setpci -s 01:00.0 F4.B=ff
sudo setpci -s 01:00.0 F4.B=00
...and...
Code:
xrandr --output <outputname> --brightness 0.8
...where <outputname> can be retrieved via:
Code:
xrandr | grep " connected"
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