Can't change backlight brightness since linux kernel 4.7

jf25 · 2016-08-13 10:03:30

Hello,
I was wondering if I'm the only one with this problem? Since yesterday's updates, I can no longer adjust the brightness of my laptop display. I usually use either the keys Fn+arrows on my keyboard or the energy settings gui of Cinnamon. None of them work any more. I also installed xorg-xbacklight and tried to set the brightness through xbacklight, but that doesn't work either (it does affect Cinnamon's brightness slider though).
Edit: /sys/class/backlight/intel_backlight does exist.

The following packages got an update:

2016-08-12 09:17:24 evince
2016-08-12 09:17:25 gd
2016-08-12 09:17:25 gvfs
2016-08-12 09:17:25 gvfs-nfs
2016-08-12 09:17:25 gvfs-smb
2016-08-12 09:17:25 iproute2
2016-08-12 09:17:33 linux
2016-08-12 09:17:50 linux-headers
2016-08-12 09:17:50 python2-pyparsing
2016-08-12 09:17:50 python-pyparsing

I think all of that gnome and python stuff is unrelated. So the only real suspect here is the linux kernel which got upgraded from 4.6.4-1 to 4.7-1. Unfortunately I couldn't find anything suspicious in the system logs (journalctl, dmesg). I can post them anyway, if somebody is interested.

So is there anybody else with this problem or does someone know a solution approach?

Thank you in advance!

Last edited by jf25 (2016-08-13 10:15:43)

Head_on_a_Stick · 2016-08-13 10:15:12

Does your backlight work again if you downgrade the kernel?

If it does, you may have suffered a kernel regression -- you can use a git bisect to find the cause and fix it:
https://wiki.archlinux.org/index.php/Bisecting_bugs

Alternatively, try the LTS kernel and see if that works:
https://www.archlinux.org/packages/core … linux-lts/

jf25 · 2016-08-13 10:38:06

Yep, downgrading linux (and linux-headers) to 4.6.4-1, "fixes" the issue. I think bisecting the kernel would be too time-consuming though. I have a thesis to write.

Head_on_a_Stick · 2016-08-13 10:39:07

Switch to the LTS kernel then, you shouldn't use an outdated kernel.

mrDoctorWho · 2016-08-13 15:39:32

Hello,

I'm actually having the same problems.

First, after the linux 4.7 update the laptop screen could go off by a timer and then it was not possible to power it on again (though, I found that if I change the tty then the screen powers on again).

Then, after the kernel was updated to 4.7-1, the backlight became broken too.

Head_on_a_Stick · 2016-08-13 17:00:00

@mrDoctorWho -- have you filed a bug report?

Does the LTS kernel work?

mrDoctorWho · 2016-08-14 02:49:02

@Head_on_a_Stick, no I actually didn't fill a bug report yet.

The LTS kernel works just fine.

Update: the screen on-off problem still exists with the LTS kernel, so I guess it's not about the kernel.

Last edited by mrDoctorWho (2016-08-14 04:28:51)

linuxchr1s · 2016-08-14 10:20:05

I got the same issue. After upgrading from 4.6 to 4.7 I found out that changing the backlight brightness doesn’t work anymore. However, the values are set correctly:

$ cat /sys/class/backlight/intel_backlight/max_brightness
4882
$ cat /sys/class/backlight/intel_backlight/brightness    
4882

jf25 · 2016-08-14 14:18:09

That's interesting. With kernel 4.7, I have the same file paths and values as linuxchr1s. With kernel 4.6 however:

$ ls /sys/class/backlight
acpi_video0    acpi_video1
$ cat /sys/class/backlight/acpi_video0/max_brightness
8
$ cat /sys/class/backlight/acpi_video0/brightness
8
$ cat /sys/class/backlight/acpi_video1/max_brightness
8
$ cat /sys/class/backlight/acpi_video1/brightness
(depends on the actual brightness)

Could it be, that this has something to do with dual gpu? I have both an Nvidia (running with open-source drivers and PRIME) and Intel GPU in my system.

By the way, switching the display on and off works like a charm for me with any kernel. So this is indeed a separate issue.

Head_on_a_Stick · 2016-08-14 16:00:55

Have any of you tried the various parameters listed in the ArchWiki?

https://wiki.archlinux.org/index.php/Ba … ne_options

jf25 · 2016-08-14 16:41:58

Great tip! I tried acpi_backlight=video and everything works again. Now I have:

$ ls /sys/class/backlight/
acpi_video0  acpi_video1  intel_backlight

Again, only the values in acpi_video1 seem to have any effect.

Thank you so much!

lviggiani · 2016-08-18 12:25:33

Head_on_a_Stick wrote:

Have any of you tried the various parameters listed in the ArchWiki?
https://wiki.archlinux.org/index.php/Ba … ne_options

I have similar issue here. Since I've upgraded to 4.7, if I set the screen brightness to any value other than 100% it starts flashing from the brightness level I've set to 100% and back.
I've tried with the kernel parameters suggested in the wiki above and with acpi_backlight = video or vendor the backlifght control does not work, whereas with acpi_backlight = native I have the same behavior as described above (flashing).
Any ideas?
This happens on a Dell XPS 13 (old ivybridge model).

Head_on_a_Stick · 2016-08-19 16:27:25

lviggiani wrote:

Any ideas?

LTS kernel, perhaps?

Does `xbacklight` work?

I set keybinds for that with my HD4600

kjslag · 2016-08-20 06:18:29

I had the same issue. Adding acpi_backlight=video to the kernel parameters solved the issue for me also.

carbohydrates · 2016-09-12 21:14:00

I am having the same problem. ThinkPad x230.

With 4.4.6, the backlight 'just works', absolutely perfectly. There's an acpi0 and intel_backlight present in /sys/class/backlight.

With 4.7.3, it doesn't. The only device present is an intel_backlight. xbacklight works, barely. The numbers are off - there are crazy floating point errors. It's impossible to inc or dec in good, round numbers. Same with acpi_backlight=video. It gives me an acpi0 device again, but it takes dozens of button presses to change the brightness even one step.

I'll take a crack at bisecting the changes to figure out what caused this regression.

Does anyone know if a bug was ever filed? It's way less usable like this...

Last edited by carbohydrates (2016-09-12 21:26:08)

lviggiani · 2016-09-12 21:38:12

Hi, I've reported the issue here
https://bugzilla.kernel.org/show_bug.cgi?id=153401
I'm currently trying to help find the commit that broken the thing.
On my Dell, as a workaround I've disabled the "Load legacy boot ROM" option from the BIOS boot menu and the backlight can now be adjusted in 4.7.2

carbohydrates · 2016-09-13 01:17:29

So setting your system to be EFI-only changes the behavior? Interesting, I'll have to try that after this enormous git repo finshes cloning

lviggiani · 2016-09-13 06:01:58

Yes... I'll check the patch mentioned in the bug report discussion and see if recompiling without it restores the old behaviour

carbohydrates · 2016-09-13 07:00:30

Sounds good - and I have a patch that works for me now

Hopefully it'll get committed so it can help everyone!

Arch Linux

#1 2016-08-13 10:03:30

Can't change backlight brightness since linux kernel 4.7

#2 2016-08-13 10:15:12

Re: Can't change backlight brightness since linux kernel 4.7

#3 2016-08-13 10:38:06

Re: Can't change backlight brightness since linux kernel 4.7

#4 2016-08-13 10:39:07

Re: Can't change backlight brightness since linux kernel 4.7

#5 2016-08-13 15:39:32

Re: Can't change backlight brightness since linux kernel 4.7

#6 2016-08-13 17:00:00

Re: Can't change backlight brightness since linux kernel 4.7

#7 2016-08-14 02:49:02

Re: Can't change backlight brightness since linux kernel 4.7

#8 2016-08-14 10:20:05

Re: Can't change backlight brightness since linux kernel 4.7

#9 2016-08-14 14:18:09

Re: Can't change backlight brightness since linux kernel 4.7

#10 2016-08-14 16:00:55

Re: Can't change backlight brightness since linux kernel 4.7

#11 2016-08-14 16:41:58

Re: Can't change backlight brightness since linux kernel 4.7

#12 2016-08-18 12:25:33

Re: Can't change backlight brightness since linux kernel 4.7

#13 2016-08-19 16:27:25

Re: Can't change backlight brightness since linux kernel 4.7

#14 2016-08-20 06:18:29

Re: Can't change backlight brightness since linux kernel 4.7

#15 2016-09-12 21:14:00

Re: Can't change backlight brightness since linux kernel 4.7

#16 2016-09-12 21:38:12

Re: Can't change backlight brightness since linux kernel 4.7

#17 2016-09-13 01:17:29

Re: Can't change backlight brightness since linux kernel 4.7

#18 2016-09-13 06:01:58

Re: Can't change backlight brightness since linux kernel 4.7

#19 2016-09-13 07:00:30

Re: Can't change backlight brightness since linux kernel 4.7

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