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#1 2023-01-12 14:29:09

evybongers
Member
Registered: 2021-04-07
Posts: 4

[SOLVED] Amdgpu backlight missing from sysfs on 6.1.4-arch1-1

Creating this forum post, because I don't know how to best report this issue.

Since I upgraded my kernel to 6.1.4-arch1-1, I found I can no longer adjust the brightness on my laptop and closer inspection shows that there's no longer any amdgpu_bl* listed in /sys/class/backlight.

$ uname -r
6.1.4-arch1-1
$ brightnessctl --class=backlight --list
Available devices:
Device 'thinkpad_screen' of class 'backlight':
	Current brightness: 0 (0%)
	Max brightness: 15

$ ls -1 /sys/class/backlight/
thinkpad_screen

Downgrading to kernel version 6.1.3-arch1-1 makes it available again.

$ uname -r
6.1.3-arch1-1
$ brightnessctl --class=backlight --list
Available devices:
Device 'thinkpad_screen' of class 'backlight':
	Current brightness: 0 (0%)
	Max brightness: 15

Device 'amdgpu_bl0' of class 'backlight':
	Current brightness: 12 (5%)
	Max brightness: 255

$ ls -1 /sys/class/backlight
amdgpu_bl0
thinkpad_screen

Is this an issue/bug with kernel 6.1.4? If so, where should I report this?

# cat /proc/cmdline
root="LABEL=Arch" resume="LABEL=Swap" rw quiet splash acpi_backlight=vendor
# lshw -class display
  *-display
       description: VGA compatible controller
       product: Picasso/Raven 2 [Radeon Vega Series / Radeon Vega Mobile Series]
       vendor: Advanced Micro Devices, Inc. [AMD/ATI]
       physical id: 0
       bus info: pci@0000:05:00.0
       version: c2
       width: 64 bits
       clock: 33MHz
       capabilities: pm pciexpress msi msix vga_controller bus_master cap_list rom
       configuration: driver=amdgpu latency=0
       resources: irq:46 memory:c0000000-cfffffff memory:d0000000-d01fffff ioport:1000(size=256) memory:d0600000-d067ffff memory:c0000-dffff

Last edited by evybongers (2023-01-13 10:43:32)

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#2 2023-01-12 17:17:20

V1del
Forum Moderator
Registered: 2012-10-16
Posts: 22,093

Re: [SOLVED] Amdgpu backlight missing from sysfs on 6.1.4-arch1-1

Try https://bbs.archlinux.org/viewtopic.php … 8#p2079038 if neither helps you'd want to make a regression report on the kernel bugzilla

Last edited by V1del (2023-01-12 17:17:51)

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#3 2023-01-13 10:42:39

evybongers
Member
Registered: 2021-04-07
Posts: 4

Re: [SOLVED] Amdgpu backlight missing from sysfs on 6.1.4-arch1-1

So, it seems removing acpi_backlight=vendor from the kernel command line did the trick. Now I wonder why I ever added that in the first place roll

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#4 2023-01-13 16:33:32

icar
Member
From: Catalunya
Registered: 2020-07-31
Posts: 469

Re: [SOLVED] Amdgpu backlight missing from sysfs on 6.1.4-arch1-1

I had "acpi_backlight=video" for more than a year because I wouldn't be able to control my screen brightness otherwise. After the kernel update mentioned, I wasn't able to control it anymore. Removing that line fixed it. One more thing that works ootb ;-)

Last edited by icar (2023-01-13 16:34:09)

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