Bug 455347

SUMMARY

After updating to KDE Plasma 5.25 the screen brightness control is showing some very erratic behavior. As I am increasing brightness it goes up and down and then up again until I reach 100% with as much as 20% effective brightness.

My `/sys/class/backlight/intel_backlight/max_brightness` shows `120000`. But monitoring `/sys/class/backlight/intel_backlight/brightness` shows it doesn't go upper than 17000.

Interestingly, as I go on and on trying to increase brightness, the value in `/sys/class/backlight/intel_backlight/brightness` increases and decreases with not apparent pattern.

I checked the journal to see if there were any errors and found this:

```
Jun 15 10:01:13 hypernova kernel: ACPI BIOS Error (bug): Could not resolve symbol [\_SB.PCI0.PEG0.PEGP.BRT6.LCD], AE_NOT_FOUND (20210331/psargs-330)
Jun 15 10:01:13 hypernova kernel:
Jun 15 10:01:13 hypernova kernel: No Local Variables are initialized for Method [BRT6]
Jun 15 10:01:13 hypernova kernel:
Jun 15 10:01:13 hypernova kernel: Initialized Arguments for Method [BRT6]:  (2 arguments defined for method invocation)
Jun 15 10:01:13 hypernova kernel:   Arg0:   000000000a60e3c0 <Obj>           Integer 0000000000000001
Jun 15 10:01:13 hypernova kernel:   Arg1:   000000001176d691 <Obj>           Integer 0000000000000000
Jun 15 10:01:13 hypernova kernel:
Jun 15 10:01:13 hypernova kernel: ACPI Error: Aborting method \_SB.PCI0.PEG0.PEGP.BRT6 due to previous error (AE_NOT_FOUND) (20210331/psparse-529)
Jun 15 10:01:13 hypernova kernel: ACPI Error: Aborting method \EV5 due to previous error (AE_NOT_FOUND) (20210331/psparse-529)
Jun 15 10:01:13 hypernova kernel: ACPI Error: Aborting method \SMEE due to previous error (AE_NOT_FOUND) (20210331/psparse-529)
Jun 15 10:01:13 hypernova kernel: ACPI Error: Aborting method \SMIE due to previous error (AE_NOT_FOUND) (20210331/psparse-529)
Jun 15 10:01:13 hypernova kernel: ACPI Error: Aborting method \NEVT due to previous error (AE_NOT_FOUND) (20210331/psparse-529)
Jun 15 10:01:13 hypernova kernel: ACPI Error: Aborting method \_SB.PCI0.LPCB.ECDV._Q66 due to previous error (AE_NOT_FOUND) (20210331/psparse-529)
```

Which indicates some hardware-related issue, which is weird because I haven updated my laptop's firmware recently. Besides, echoing to `/sys/class/backlight/intel_backlight/brightness` works as expected.

Also, a think I am not alone in this one, see this reddit thread: https://www.reddit.com/r/kdeneon/comments/vcpx9c/cant_adjust_brightness/

STEPS TO REPRODUCE

1. Try to increase/decrease screen brightness

OBSERVED RESULT

Screen brightness shows erratic behavior.

EXPECTED RESULT

Screen brightness should increase or decrease accordingly.


SOFTWARE/OS VERSIONS

Linux/KDE Plasma: 5.25.0
(available in About System)
KDE Plasma Version:  5.25.0
KDE Frameworks Version: 5.95.0
Qt Version: 5.15.4

ADDITIONAL INFORMATION

Laptop model: Dell XPS 15 (7590).
Graphics platform: X11
Graphics processor: Mesa Intel UHD Graphics 630