Arch Linux

pixelbook

Member

Registered: 2026-07-08

Posts: 3

2017 Pixelbook backlight control doesn’t work with 7.1.x kernel

I tried to get help in reddit /r/linux questions and also mrchromebox forums, but I don't think anyone in those forums have any idea what changed in Linux 7.1.x kernel changes this and how to fix. I've gone ahead and reported a regression to the kernel bug tracker for linux.

**System Details**

Device: 2017 Google Pixelbook i5 (Google's own chromebook from 2017)
Backlight: intel_backlight
OS: Arch using KDE Plasma 6.7.2 (Wayland via Kwin)
Firmware Type: RW_LEGACY firmware from MrChromeBox, updated to most recent version
Internal storage type: SSD

**Summary of the Issue**

The Pixelbook has pretty much full functionality with linux, except for two needed tweaks. Once is a chromebook audio script to run, and the other is backlight.

Adjusting the backlight (using the slider in KDE) does not work without editing your GRUB file and putting in this line: GRUB_CMDLINE_LINUX=“i915.enable_dpcd_backlight=1”

This “fix” has worked with any flavor of linux. I have personally tested in Kubuntu, MX Linux, CachyOS, and now Arch.

The problem now is, something changed with the Linux 7.1 kernel where this doesn’t work anymore. Still works perfectly on 7.0.x kernel and below, but any 7.1 (or 7.2rc kernel) does not work and I’ve tried a million fixes, and nothing works. The million fixes include removing that line, changing the value to 0, 2, or 3.

Tried this, didn’t work: GRUB_CMDLINE_LINUX=“i915.enable_dpcd_backlight=1 i915.enable_psr=0 i915.enable_fbc=0” Also tried GRUB_CMDLINE_LINUX=“acpi_backlight=native”

I have tried the software brightnessctl, making changes with it has no effect. Also tried the software gammastep, doesn’t work. And other ones like “colord” (I think that’s what it is called).

I've read the backlight section in arch wiki, nothing there that works to fix this.

NOTHING changes the brightness if using 7.1.x or newer kernel. This includes 7.2rc kernels.

**Steps to Reproduce**

1.) Install RW_LEGACY MrChromebox firmware on Pixelbook and any flavor of Linux with kernel 7.1 or higher.

2.) Edit GRUB_CMDLINE_LINUX=“i915.enable_dpcd_backlight=1” and update grub. This is the fix for backlight controls that works for kernel 7.0.x and lower.

3.) With 7.1 kernel or higher, this fix does not work, neither do any other known fixes for controlling backlight.

**Expected Behavior**

I should be able to use the slider in KDE for backlight/brightness and adjust the brightness, just as I can do with any kernel 7.0.x or lower. I have reached the conclusion that something changed in the 7.1 kernel, but have no idea on how to get this fixed. Or if it is even possible. Perhaps I am stuck just using 7.0.x and below on this device until EOL.

Thank you!!

Last edited by pixelbook (2026-07-08 20:33:49)

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 25,285

Re: 2017 Pixelbook backlight control doesn’t work with 7.1.x kernel

try setting that enable_dpcd_backlight to 2 (or 3) instead of 1. FWIW there was quite a bit of work on this part of the kernel code so potentially some regression or so, so even if this might be fixable with adjustments to this params value, you probably want to report this here: https://gitlab.freedesktop.org/drm/i915 … work_items

Last edited by V1del (2026-07-08 21:48:37)

pixelbook

Member

Registered: 2026-07-08

Posts: 3

Re: 2017 Pixelbook backlight control doesn’t work with 7.1.x kernel

Thanks for responding. As mentioned in my post, I did try setting it to 2 and 3, neither worked. I also reported a regression to the linux devs as mentioned above, so maybe it will get fixed in the future. I keep linux-mainline installed for this particular testing purpose, and as of yet, it's not fixed.

I mentioned being "stuck" on 7.0.x kernel, but shouldn't do that because of lack of security updates. For now, I'm running the LTS kernel.

Last edited by pixelbook (2026-07-09 02:14:11)

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 25,285

Re: 2017 Pixelbook backlight control doesn’t work with 7.1.x kernel

Ah whoops, sorry read over that, how this code behaves has been changed quite a bit in this version range so likely some regression in the detection logic there

pixelbook

Member

Registered: 2026-07-08

Posts: 3

Re: 2017 Pixelbook backlight control doesn’t work with 7.1.x kernel

After reporting the regression, the linux devs asked me to do a git bisect. I did it and found the offending commit and reported it:

b3793af3277f65d256d67f9949e760b434ff66dd is the first 'bad' commit
commit b3793af3277f65d256d67f9949e760b434ff66dd
Merge: 51cc1c427461 88919bedabb8
Author: Jiri Kosina <jikos@kernel.org>
Date:   Thu Apr 16 21:08:14 2026 +0200

   Merge branch 'for-7.1/intel-thc' into for-linus

   - power management improvements to intel-thc-hid driver (Even Xu)

drivers/hid/intel-thc-hid/intel-quickspi/pci-quickspi.c | 16 ++++++++++------
drivers/hid/intel-thc-hid/intel-thc/intel-thc-dev.c     | 47
+++++++++++++++++++++++++++++++++++++++++++++++
drivers/hid/intel-thc-hid/intel-thc/intel-thc-hw.h      |  4 ++++
3 files changed, 61 insertions(+), 6 deletions(-)

They asked me to do further things, but it is beyond my ability. Honestly, sounded like they don't believe the result of my git bisect as being the culprit. You'd think they would run with the offending commit and see what they can do on their end, but I guess not.

seth

Member

From: Won't reply 2 private help req

Registered: 2012-09-03

Posts: 76,886

Re: 2017 Pixelbook backlight control doesn’t work with 7.1.x kernel

They asked me to do further things, but it is beyond my ability. Honestly, sounded like

Link?
What "further things"?

You'd think they would run with the offending commit and see

… whether they also have a pixelbook from 2017…?

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