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#1 2016-04-22 16:12:57

davcri
Member
From: Italy
Registered: 2015-04-29
Posts: 26

[Gnome] Backlight doesn't work

I can't change backlight from Gnome, but I can do it with Cinnamon, Mate and Xfce.

I found out that changing backlight with Gnome (both with keys or the slider on the top-right corner) affects

/sys/class/backlight/nv_backlight/brightness

instead of 

/sys/class/backlight/intel_backlight/brightness
# manually echoing values to this file, changes display brightness! 

I have an Acer 5750g notebook with a Intel integrated GPU (i7 2630qm with HD graphics) and Nvidia discrete GPU (540m).
I tried, without success, all the kernel command line options from: https://wiki.archlinux.org/index.php/ba … ne_options

I found this bug report that is similar to my problem: https://bugzilla.redhat.com/show_bug.cgi?id=1268091
Is this a Gnome bug ? What I should do ? Is there a way to tell Gnome to use the correct path when changing brightness?

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#2 2016-04-23 00:46:44

JohnBobSmith
Member
From: Canada
Registered: 2014-11-29
Posts: 804

Re: [Gnome] Backlight doesn't work

If your issue is DE specific, then it may be the keybinds are incorrect. If you can, look for a keybindings file within gnome, then look for any bind with XF86 in it, as those are more likely to correspond to brightness if I remember correctly. Brightness settings in general should not be tied directly to a DE, so the following may also help: https://wiki.archlinux.org/index.php/Backlight


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#3 2016-04-23 12:13:23

davcri
Member
From: Italy
Registered: 2015-04-29
Posts: 26

Re: [Gnome] Backlight doesn't work

Wiki page didn't help much with this problem hmm
I'll search for gnome keybindings! But really I don't know where to start.

Brightness settings in general should not be tied directly to a DE

I thought the same but... Gnome is strange!  If I disable the Nvidia GPU from the bios, Gnome works fine (maybe because there is no ambiguity in '/sys/class/backlight/'

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#4 2016-04-25 16:18:20

davcri
Member
From: Italy
Registered: 2015-04-29
Posts: 26

Re: [Gnome] Backlight doesn't work

I digged in and found that both Nvidia and Intel GPU are of the same type RAW: now it's explained why changing kernel parameters doesn't have any effect!
Unfortunately the problem is still there.

○ → cat /sys/class/backlight/intel_backlight/type 
raw

○ → cat /sys/class/backlight/nv_backlight/type 
raw

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#5 2016-05-02 12:33:07

davcri
Member
From: Italy
Registered: 2015-04-29
Posts: 26

Re: [Gnome] Backlight doesn't work

In the meantime I found a couple of workarounds:
- Blacklisting the nouveau module fixes the problem (but it's similar to disable the GPU from the bios)
- Installing nvidia proprietary drivers:  "/sys/class/backlight" contains only "intel_backlight".

I'm using the first fix because I need the GPU on Windows but I don't need it on Arch.
I guess I'll have to report to Gnome developers to investigate further in the main issue.

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