[Bug 198907] Backlight control missing with /sys/class/backlight/ empty

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=198907

Manuel (m.linsmayer at expersite.com) changed:

           What    |Removed                     |Added
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                 CC|                            |m.linsmayer at expersite.com

--- Comment #6 from Manuel (m.linsmayer at expersite.com) ---
Hello!

I have a very similar situation, in my opinion. I'm running kernel 4.15.0-20,
my distro is Kubuntu 18.04, my hardware is a Dell XPS 15 9560 running with
latest firmware (1.9.4) in UEFI mode.

/sys/class/backlight is also empty for me. I have an Intel 591B as well as an
discrete NVIDIA GeForce GTX 1050. Situation is the same, no matter whether I'm
using Intel or NVIDIA graphics.

I'm also getting ACPI errors at startup.

[    0.000000] ACPI: Core revision 20170831
[    0.000000] ACPI Error: [\_SB_.PCI0.XHC_.RHUB.HS11] Namespace lookup
failure, AE_NOT_FOUND (20170831/dswload-210)
[    0.000000] ACPI Exception: AE_NOT_FOUND, During name lookup/catalog
(20170831/psobject-252)
[    0.000000] ACPI Exception: AE_NOT_FOUND, (SSDT:xh_rvp11) while loading
table (20170831/tbxfload-228)
[    0.000000] ACPI Error: 1 table load failures, 12 successful
(20170831/tbxfload-246)

I'm able to see ACPI events when pressing brightness down/up buttons:

 9DBB5994-A997-11� 000000d0 00000000
video/brightnessdown BRTDN 00000087 00000000 K
 9DBB5994-A997-11� 000000d0 00000000
video/brightnessup BRTUP 00000086 00000000 K

I played around with acpi_osi and acpi_backlight, but this doesn't change
anything.

Manuel

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