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<2020-12-09> by Lorenzo Bolla

Backlight control on XPS

This post is more of a reminder for myself on how I fixed an issue with Dell XPS 15.

The issue is that the Fn key to control screen brightness (using F11 and F12) doesn't work and results in this error in the logs:

[42134.228185] ACPI BIOS Error (bug): Could not resolve symbol [\_SB.PCI0.PEG0.PEGP.BRT6.LCD], AE_NOT_FOUND (20190816/psargs-330)
[42134.228216] No Local Variables are initialized for Method [BRT6]
[42134.228220] Initialized Arguments for Method [BRT6]:  (2 arguments defined for method invocation)
[42134.228222]   Arg0:   000000008e36102a <Obj>           Integer 0000000000000002
[42134.228232]   Arg1:   00000000cd43b166 <Obj>           Integer 0000000000000000
[42134.228247] ACPI Error: Aborting method \_SB.PCI0.PEG0.PEGP.BRT6 due to previous error (AE_NOT_FOUND) (20190816/psparse-529)
[42134.228692] ACPI Error: Aborting method \EV5 due to previous error (AE_NOT_FOUND) (20190816/psparse-529)
[42134.229069] ACPI Error: Aborting method \SMEE due to previous error (AE_NOT_FOUND) (20190816/psparse-529)
[42134.229455] ACPI Error: Aborting method \SMIE due to previous error (AE_NOT_FOUND) (20190816/psparse-529)
[42134.229734] ACPI Error: Aborting method \NEVT due to previous error (AE_NOT_FOUND) (20190816/psparse-529)
[42134.229999] ACPI Error: Aborting method \_SB.PCI0.LPCB.ECDV._Q66 due to previous error (AE_NOT_FOUND) (20190816/psparse-529)

The error has been reported many times in the last year.

The only thing that worked for me was using this: icc-brightness. It is basically a workaround the BIOS/Kernel issue, but it works very well.