Somewhere between kernel 4.19 and 5.6 my laptop backlight key (F5 / F6) stopped working. Backlight or screen brightness does work when using the slider in Gnome. To be completely accurate, I could also state that the issue showed up between Debian 10 and Debian Testing.
To rule out hardware issues, I installed a fresh copy of Debian 10 with the Gnome desktop, pressed F5 and the graphic showing the backlight key had been pressed, showed up. I then installed a fresh copy of Debian Testing, pressed F5, and no graphic. It's like the keypress isn't getting registered. Again, in both cases, moving the slider in the Gnome control panel does what it is supposed to do, and the backlighting is adjusted.
Details about how my backlighint work may be important, so I'll explain them here. My laptop is old, it's a 2012 Sony VPCEG Vaio. When I first installed Linux, the backlight controls, both hardware and through Gnome didn't work. I found an old bug report about something similar and used this "work around" to get things going. I created two files:
$ cat /etc/udev/rules.d/99-writeintelbacklight.rules
Code: Select all
ACTION=="change", SUBSYSTEM=="backlight", RUN+="/usr/sbin/writeintelbacklight.sh"
Code: Select all
#!/bin/bash
intelmaxbrightness=`cat /sys/class/backlight/intel_backlight/max_brightness`
acpimaxbrightness=`cat /sys/class/backlight/acpi_video0/max_brightness`
scale=`expr $intelmaxbrightness / $acpimaxbrightness`
acpibrightness=`cat /sys/class/backlight/acpi_video0/brightness`
newintelbrightness=`expr $acpibrightness \* $scale`
curintelbrightness=`cat /sys/class/backlight/intel_backlight/actual_brightness`
if [ "$newintelbrightness" -ne "$curintelbrightness" ]
then
echo $newintelbrightness > /sys/class/backlight/intel_backlight/brightness
fi
exit 0
I was reading through the Arch Wiki (https://wiki.archlinux.org/index.php/Backlight) and under the section "Unable to control eDP Panel brightness (Intel i915 only)" I read "Note: The parameter changed from bool to int in linux 5.4." When Linux boots, I see i915 all the time, so I know my system uses that module or whatever it is. Though not specific to my problem, I wonder if other changes were made in the 5.4 kernel that break my work around.
I think it is relevant to note, that even without my "work around" pressing the F5 / F6 keys always resulted in the backligh graphic displaying on the screen. It didn't do anything but the key triggered the graphic. That is no longer the case, no graphic.
If anyone can help, or point me in the right direction, I'd appreciate it! Thank you.