Arch Linux

NESO

Member

Registered: 2018-07-02

Posts: 5

[SOLVED]Cannot change brightness on Intel laptop w/Plasma 5 after boot

Hello. I've recently reinstalled Arch on my laptop, and now can't change backlight brightness after boot, neither using Fn keys nor Plasma's bright controls. I've checked several posts and the wiki, and tried suggestions like modifying kernel parameters, but none of those have worked at all. The bright level keeps at maximum. I've also checked

/sys/class/backlight

and there's only intel_backlight folder.
There's no 20-intel.conf file at xorg.conf.d folder, and this problem happens when using xf86-video-intel driver and also with modeset driver. My device is a 4th Gen Intel laptop with NVIDIA Optimus technology, and I also installed nouveau driver for using the NVIDIA graphics card with DRI_PRIMUS=1 variable before the app I want to run.
At /etc/modprobe.d/i915.conf I've only set

options i915 enable_fbc=1

and I guess nouveau is not blacklisted (but I can't remember how to check this).
lspci output:

lspci | grep 'VGA\|3D\|2D'
00:02.0 VGA compatible controller: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller (rev 06)
01:00.0 3D controller: NVIDIA Corporation GF117M [GeForce 610M/710M/810M/820M / GT 620M/625M/630M/720M] (rev a1)

Possibly relevant kernel parameters:

loglevel=3 i915.fastboot=1 rd.systemd.show_status=auto rd.udev.log_priority=3 vt.global_cursor_default=0

(Didn't posted hard drive parameters)

mkinitcpio.conf modules:

MODULES=(i915)

mkinitcpio.conf hooks:

HOOKS=(base systemd sd-plymouth autodetect keyboard sd-vconsole modconf block sd-encrypt sd-lvm2 filesystems fsck)

A curious fact about this is that, when run

$ xset dpms force off

and wake up the screen; or when wake up the device after a suspension, I can change the bright level normally.
How can I fix this?
PS: if needed, I can post more outputs.

[EDIT] This problem was solved by removing i915.fastboot=1 kernel parameter. According to Arch Wiki about Intel Graphics - Fastboot, that kernel parameter can cause problems on pre-Skylake systems, but I never expected that could conflict with backlight.
Just for reference, my laptop is MSI-CX61-2PC, with Intel Core i7-4712MQ with Intel® HD Graphics 4600 (Haswell architecture, pre-Skylake) and NVIDIA GeForce 820M.

Last edited by NESO (2019-05-03 15:47:25)

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 25,423

Re: [SOLVED]Cannot change brightness on Intel laptop w/Plasma 5 after boot

Problems like these are almost always vendor specific, which actual laptop are we talking here? FWIW check for BIOS/UEFI updates they often contain fixes for that, what happens if you remove the two intel related kernel parameters?

NESO

Member

Registered: 2018-07-02

Posts: 5

Re: [SOLVED]Cannot change brightness on Intel laptop w/Plasma 5 after boot

It seems that removing i915.fastboot=1 kernel parameter did the trick.
I've found a bug report where they get the same problem, with similar hardware: https://bugs.freedesktop.org/show_bug.cgi?id=108225.
Thank you.
Marking as solved.