Some two years ago, I was able to set a very dim backlight brightness by writing a non-integer value to /sys/class/backlight/intel_backlight/brightness.
$ echo 0.3 > /sys/class/backlight/intel_backlight/brightness
But now, it seems that there is some sanity check... so, the system complains:
bash: echo: write error: Invalid argument
Is there anyway I can bypass such sanity check? Is there a way to pass values directly to the driver? I believe the relevant driver is i915.
Linux debiel 5.4.0-4-amd64 #1 SMP Debian 5.4.19-1 (2020-02-13) x86_64 GNU/Linux
Please, let me know if I should have given you any useful information. I do not really know how to properly report the problem.