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#1 2019-01-30 04:10:56

vastabo
Member
Registered: 2019-01-21
Posts: 7

Dell XPS 9370 Screen Brightness

Hello there,

I need some help figuring out why I can't adjust the screen backlight setting on my Dell XPS 9370.

I have made extensive use of the Backlight article on the Arch wiki. Here's the situation:

$ ls -l /sys/class/backlight/

lrwxrwxrwx 1 root root 0 Jan 30 03:04 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight

Unlike some other, similar posts I only have Intel graphics. Descending into that directory reveals a familiar cast of characters:

actual_brightness  bl_power  brightness  device  max_brightness  power  subsystem  type  uevent

# cat brightness

3276

# echo 1 > brightness

No effect on the backlight, though it does change the value of /sys/class/backlight/intel_backlight/brightness.

Now that "eDP-1" harkens to a section on that wiki labeled Unable to control eDP Panel brightness (Intel i915 only). Therefore:

$ cat /etc/modprobe.d/i915.conf

options i915 enable_dpcd_backlight=1

Again, no effect.

Both the Backlight  and Intel Graphics articles suggest several kernel parameters to address this problem:

  • acpi_backlight=video

  • acpi_backlight=vendor

  • acpi_backlight=native

These will variously add "acpi_video0" and "dell_backlight" to /sys/class/backlight but these also do not adjust the backlight.

  • acpi_osi=Linux

  • acpi_osi="!Windows 2012"

  • acpi_osi=

Don't seem to have any effect.

Installing xf86-video-intel will allow xbacklight to find a backlight, but it can't adjust it. It will also allow:

$ xrandr --output eDP1 --brightness .8

...to function but that's a software hack (and I want to continue using the modesetting driver if I can help it).

Some have suggested that Dell's Content Adaptive Brightness Control is interfering; I have disabled that in the firmware settings (though I did not apply the patch Dell supplies to do this; it requires Windows). Also, it does not seem matter to Ubuntu because:

The brightness adjustment works out of the box with Ubuntu, including the function keys.

I've been poking around in there to see how they got it to work (kernel params, modprobe settings, using acpid, etc.) but nothing seems to work in Arch. I tried using the linux-lts kernel as well as linux-zen to no avail.

Anyway, I'm running out of ideas. Can anyone help?

Thanks

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#2 2019-02-13 10:24:12

andym
Member
From: France
Registered: 2019-01-16
Posts: 5

Re: Dell XPS 9370 Screen Brightness

Have you checked this debug page

Andrew

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#3 2019-02-13 21:57:20

cgorichanaz
Member
Registered: 2018-03-23
Posts: 10

Re: Dell XPS 9370 Screen Brightness

I've been experiencing this issue for several days but have not pinpointed it. I've tried everything OP tried with similar results. I assumed it had something to do with my having recently installed acpid to help with some lid open/close scripting, but now that I uninstalled that, I have the same behavior. I tried rolling back the kernel to 4.20.6.arch1-1 but same results. I'll have to revisit this next week.

Last edited by cgorichanaz (2019-02-15 22:28:37)

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#4 2019-02-20 00:47:52

vastabo
Member
Registered: 2019-01-21
Posts: 7

Re: Dell XPS 9370 Screen Brightness

andym wrote:

Have you checked this debug page

Andrew

Yes, I had.

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#5 2019-02-20 00:59:08

vastabo
Member
Registered: 2019-01-21
Posts: 7

Re: Dell XPS 9370 Screen Brightness

cgorichanaz wrote:

I've been experiencing this issue for several days but have not pinpointed it. I've tried everything OP tried with similar results. I assumed it had something to do with my having recently installed acpid to help with some lid open/close scripting, but now that I uninstalled that, I have the same behavior. I tried rolling back the kernel to 4.20.6.arch1-1 but same results. I'll have to revisit this next week.

Sorry about the delay; I wasn't subscribed to this topic.

I managed to workaround it by enabling "Legacy Boot" in the firmware and then reinstalling GRUB on the MBR (BIOS Mode).

Furthermore, I had to install the xf86-video-intel driver to allow xbacklight function correctly.

I have not yet fixed the function keys to control the backlight but I can echo integers into /sys/class/backlight/intel_backlight/brightness to the same effect.

This solution seems very hack-y to me so I'm reluctant to marked it "solved".

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#6 2019-02-21 05:57:40

cgorichanaz
Member
Registered: 2018-03-23
Posts: 10

Re: Dell XPS 9370 Screen Brightness

I spent much of this past weekend troubleshooting to no avail. In that process I realized I did not need xf86-video-intel in general, so I removed that. I haven't changed anything in the BIOS but have CABC disabled and legacy boot disabled, and I use systemd-boot. I decided to boot the Arch installer from USB to see if it was somehow a hardware problem (even though within the BIOS the brightness can be demonstrably changed, although frustratingly the values never seemed to save). Within the installer, my backlight keys worked fine. I booted back into my normal installation and noted the backlight keys again did not work. So I decided to give up again. And then some point in the next few hours, I accidentally hit the backlight keys and noticed they worked! I do not think I changed any configuration between when they did not work and when they worked. It makes me fear there is some state interfering, similar to have the Bluetooth sometimes stops working until you do a cold reboot. I'm very exhausted of this, but, if I get some time, I will try to backtrack and see if I can identify any changes that might trigger.

So, apparently I have no problem using xbacklight (from acpilight package) or echoing to /sys/class/backlight/intel_backlight/brightness WITHOUT xf86-video-intel installed (and my X config is simpler now, using only mesa package).

In case anyone has infinite time and determination or know what he or she is looking for, I put some data about my system and config at https://github.com/CNG/dotfiles/tree/ma … brightness

Last edited by cgorichanaz (2019-02-21 06:00:13)

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#7 2019-03-03 18:19:53

cgorichanaz
Member
Registered: 2018-03-23
Posts: 10

Re: Dell XPS 9370 Screen Brightness

Shortly after my last message, the problem recurred and I have not been able to fix it yet. For now I have settled on rebooting the computer and quickly setting my desired brightness level while the DELL logo shows, and any time I want to change the brightness, reboot the computer...

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#8 2019-03-03 19:02:21

CarbonChauvinist
Member
Registered: 2012-06-16
Posts: 141

Re: Dell XPS 9370 Screen Brightness

vastabo wrote:

I have not yet fixed the function keys to control the backlight but I can echo integers into /sys/class/backlight/intel_backlight/brightness to the same effect.

@cgorichanaz & vastabo - are you sure this isn't simply the function lock that's available on Dell keyboards? If you press the Fn+ESC keys at the same time that can toggle on or off the function lock. With the function lock on -- the F{1-12} keys pressed on their own act as the media keys. If the function lock is off -- you'll need to press the Fn + F{1-12} to engage the media player or screen controls etc.


"the wind-blown way, wanna win? don't play"

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#9 2019-03-08 02:03:42

cgorichanaz
Member
Registered: 2018-03-23
Posts: 10

Re: Dell XPS 9370 Screen Brightness

Hi @CarbonChauvinist, for my reports at least, the echoing to the brightness sys file has never had an effect when my backlight keys were not working (including now, sadly), aside from setting to 0 turns off the backlight. Just to be sure, I tried your suggestion. Further evidence the keys are working is when I use the brightness down key repeatedly, the screen eventually turns off. At that point, hitting the brightness up button turns the screen back on, but repeating does not change the brightness from what it was at the time the system booted past the Dell logo.

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#10 2019-03-09 00:48:57

vastabo
Member
Registered: 2019-01-21
Posts: 7

Re: Dell XPS 9370 Screen Brightness

@CarbonChauvinist  No, I thought of that; FnLock does not allow the hardware keys to work. I haven't devoted any time to fixing them, however.

@cgorichanaz The only reason I installed (and still have) xf86-video-intel is to allow the xbacklight utility to correctly report brightness levels to Polybar's backlight module; the video driver is a red herring.

Installing Arch in legacy/BIOS mode is what allowed `echo 500 > /sys/class/backlight/intel_backlight/brightness` to work. I honestly have no idea how or why the backlight interface works except that it's handled by the kernel. I briefly looked at the source tree but don't understand what it's doing.

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#11 2019-04-23 06:00:40

cgorichanaz
Member
Registered: 2018-03-23
Posts: 10

Re: Dell XPS 9370 Screen Brightness

Well I'm still plagued by this issue. For the last 6 weeks I have been unable to change screen brightness except upon restarting... so I have been restarting very frequently. wink

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#12 2019-04-23 16:23:48

vastabo
Member
Registered: 2019-01-21
Posts: 7

Re: Dell XPS 9370 Screen Brightness

I don't know if you've tried this already, but...

1) Burn a USB stick with Arch
2) Reboot. Enter the XPS 13's "BIOS Setup" (F2 key at startup, I think). Enable "Legacy Boot Mode". You might also disable Adaptive Brightness while you're there.
3) Boot off the USB stick. You'll know if you're in BIOS mode if Arch's boot menu is fairly graphical (I can't describe it better than that; try it both ways and you'll see a difference)
4) You'll be at a root shell. Run `echo 500 > /sys/class/backlight/intel_backlight/brightness`.

It worked for me.

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#13 2019-04-29 05:23:03

cgorichanaz
Member
Registered: 2018-03-23
Posts: 10

Re: Dell XPS 9370 Screen Brightness

Are you saying running that command at root shell when booted from Arch on USB has restored your ability to change the brightness with the brightness up/down keys once booted back into your regular Arch installation?

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#14 2019-04-29 16:16:27

vastabo
Member
Registered: 2019-01-21
Posts: 7

Re: Dell XPS 9370 Screen Brightness

No, it was just a fast way of testing if BIOS/UEFI boot was a factor affecting this screen brightness problem.

It is.

My regular Arch installation (that I'm typing this on) is booted in legacy (BIOS) mode so I can adjust the brightness. I'm sure you'll agree that this is sub-optimal but I haven't made time to revisit this problem.

I'm kind of hoping someone who knows more than me will visit this thread with a better solution.

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#15 2019-08-12 06:43:21

cgorichanaz
Member
Registered: 2018-03-23
Posts: 10

Re: Dell XPS 9370 Screen Brightness

I had somehow solved the issue for a few weeks, and before I got to narrow it down for a writeup, I unsolved it... and now I can't figure out what changed, but I am back to no control after booting. I'll try to post back here more promptly if I figure it out again.

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#16 2019-08-13 01:10:17

vastabo
Member
Registered: 2019-01-21
Posts: 7

Re: Dell XPS 9370 Screen Brightness

I would appreciate it. Thanks!

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#17 2019-08-23 07:56:31

cgorichanaz
Member
Registered: 2018-03-23
Posts: 10

Re: Dell XPS 9370 Screen Brightness

All right, the way I currently fixed this was by removing enable_dpcd_backlight from my /etc/modprobe.d/i915.conf. That file now contains this line only:

options i915 modeset=1 enable_psr=2 enable_fbc=1 enable_guc=2 fastboot=1

Then the other thing I had to do previously (which I thought was the only thing till I accidentally reverted the i915.conf change above) is remove i915 from the MODULES=() block in my /etc/mkinitcpio.conf file and regenerate the boot image (which I had done by reinstalling the linux package to be sure I didn't accidentally use the wrong syntax calling the utility directly).

It does not seem to matter what dynamic backlight setting I have in the BIOS.

Full disclosure: I have not reviewed everything above in this thread for months, so if there's more detail about other parts of my setup you need, let me know. I do hope to reassess all parts of my install sometime.

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