Backlight/brightness controls stopped working

AmagicalFishy · 2021-02-06 10:58:26

I've tried all of the solutions I can find. This includes:

Adding "video.use_native_backlight=0" to the kernel parameters
Every option of "acpi_backlight=..."
Adding:
- video.only_lcd=0
- acpi_osi='Windows 2009'
- acpi_osi = '!Windows 2015'

... and several other kernel parameters/combination-of-parameters. My dmesg suggests:

i915 0000:00:02.0: [drm] Panel advertises DPCD backlight support, but VBT disagrees. If your backlight controls don't work try booting with i915.enable_dpcd_backlight=1. If your machine needs this, please file a _new_ bug report on drm/i915, see https://gitlab.freedesktop.org/drm/intel/-/wikis/How-to-file-i915-bugs for details.

So I've tried adding this too.
- Using "light" and "xbacklight" (both of which *seem* to work, but have no actual affect on the brightness)

I used to alter /sys/class/backlight/intel_backlight/brightness manually to control my brightness. That used to work well until a system update ~week ago.

The output of "lspci | rg VGA" is

00:02.0 VGA compatible controller: Intel Corporation UHD Graphics 630 (Mobile)
01:00.0 VGA compatible controller: NVIDIA Corporation GP106M [GeForce GTX 1060 Mobile] (rev a1)

The output of "lsmod | rg video" is

video                  53248  1 i915

And the output of "modinfo video" is

filename:       /lib/modules/5.10.11-arch1-1/kernel/drivers/acpi/video.ko.xz
license:        GPL
description:    ACPI Video Driver
author:         Bruno Ducrot
srcversion:     91BB2F5F38A38654A9225AD
alias:          acpi*:LNXVIDEO:*
depends:        
retpoline:      Y
intree:         Y
name:           video
vermagic:       5.10.11-arch1-1 SMP preempt mod_unload 
sig_id:         PKCS#7
signer:         Build time autogenerated kernel key
sig_key:        60:02:54:23:B9:E9:F0:B3:BF:0D:F4:03:96:8A:2D:A4:6D:3E:97:E6
sig_hashalgo:   sha512
signature:      1D:A8:D0:C3:41:23:DE:3D:9B:93:9F:B6:D5:54:FE:19:18:3F:FA:C7:
                E3:69:0F:C3:D8:9E:E0:E1:4E:9D:7B:93:DC:B8:96:FA:B1:65:78:A3:
                74:DC:6D:B2:26:7B:E1:A4:4D:06:6E:18:D8:19:D7:64:19:FA:80:30:
                AF:A8:D1:5E:F8:DB:0E:68:8F:66:17:75:88:0C:4F:5A:60:6D:21:76:
                E1:CE:0B:F9:4D:B1:03:DD:A4:06:72:E4:F1:13:26:8A:CC:E1:A4:39:
                51:09:E7:CA:F5:06:28:2B:8E:87:01:30:85:84:A7:AD:52:17:16:2E:
                A7:31:B7:50:6C:16:00:CF:DD:85:25:27:FC:A9:54:24:CC:C0:6E:B6:
                68:76:A6:DE:9D:7A:B4:BD:AF:EF:65:FC:57:52:A4:D5:ED:49:E3:FA:
                02:DA:B2:0E:41:5B:96:9B:89:32:95:D1:38:E8:2B:F3:19:5E:F1:B0:
                D7:38:09:5E:28:54:BE:06:77:42:CB:CC:33:28:71:9E:C9:FA:4B:57:
                28:6C:A5:5B:B4:BE:75:B0:E9:DA:8C:90:CA:38:8C:7F:CE:61:EF:57:
                D3:D5:DE:4D:DD:80:C9:DB:28:32:1E:DF:57:8A:F8:53:28:0D:38:56:
                7B:49:72:DF:43:BF:26:51:51:5A:A5:27:FE:D3:E4:EE:5D:5E:80:C0:
                0C:EF:01:BE:C9:EA:2F:08:28:4B:FA:01:21:FC:09:29:8C:09:E5:95:
                EA:C6:15:0D:FC:92:66:CD:38:0F:DE:19:C9:B0:1C:DC:FD:A9:A5:0D:
                34:D6:C2:28:EF:8D:66:06:54:BD:C5:96:68:9F:A9:8D:24:DF:A4:4F:
                D0:D7:4F:56:BB:53:62:70:CB:3A:CE:A1:92:15:D2:89:A5:33:05:ED:
                13:1F:8D:0C:8F:D5:3A:0F:BC:1E:72:D7:F4:7F:D2:7E:22:CD:1F:79:
                98:6F:5B:EB:1A:E7:B8:10:24:F2:6F:8B:4C:10:A6:37:6C:63:CA:46:
                75:4B:37:08:28:5A:CD:FA:40:B1:EF:7F:18:4B:E3:62:4D:E2:26:A0:
                68:27:8F:60:06:00:E0:C5:8E:23:71:35:C1:0A:44:0E:D1:3B:2C:54:
                39:C1:1D:7D:26:9F:EA:FE:79:25:E3:99:E0:7E:12:90:43:0A:2D:85:
                1F:7C:E4:B0:B8:94:94:26:64:C8:02:D5:B4:03:C4:74:91:C1:38:5B:
                68:F1:DA:9D:FB:F4:12:1C:8D:27:EC:52:6E:6E:4D:0F:4C:C7:98:18:
                5A:A7:6A:13:D5:BA:EF:17:E6:58:71:1D:30:3B:A7:58:D8:E5:4E:2F:
                CB:8F:69:E0:BD:96:8F:C5:C5:03:E1:45
parm:           brightness_switch_enabled:bool
parm:           allow_duplicates:bool
parm:           disable_backlight_sysfs_if:int
parm:           report_key_events:0: none, 1: output changes, 2: brightness changes, 3: all (int)
parm:           hw_changes_brightness:Set this to 1 on buggy hw which changes the brightness itself when a hotkey is pressed: -1: auto, 0: normal 1: hw-changes-brightness (int)
parm:           device_id_scheme:bool
parm:           only_lcd:int

And those're just the solutions I can remember off the top of my head. >.<

The brightness of my monitor is not responding to *anything* unless the value in /sys/.../backlight is 0, in which case it turns off.

Anyone have any ideas?

Maniaxx · 2021-02-06 21:40:56

Just a wild shot... there is 'ddcutil' that is able to control brightness of LCD panels. Not sure if that might help in any way.

adomol · 2021-02-07 00:16:42

Did you add your user to group video for the light package?

AmagicalFishy · 2021-02-07 12:40:15

My user is in the video group, yeah.

I tried "ddcutil" too and that didn't work.

It's just totally unresponsive.

Maniaxx · 2021-02-07 17:53:30

It might help to enable debug mode for the corresponding kernel modules. Which ones and how needs to be determined.

brandon.arnold · 2021-02-27 23:09:38

I'm in the same situation as op. I was a little late updating my kernel until a few days ago, and the brightness controls have stopped working.

When it worked, I followed the ACPI approach in the Backlight Archwiki. I made things easier using the light package as well as kernel parameter i915.enable_dpcd_backlight=1, required by my system.

Expected behavior is that the value of /sys/class/backlight/intel_backlight/brightness, between 0 and 255, corresponds with the brightness of my display. The actual behavior, however, is I get the same brightness when this file is set to integers from 1-255, and the display is turned off when it is a value of 0. Another interesting thing I've noticed is that when I reboot, the display does not stay the same brightness. I haven't investigated this enough, but I suspect it may be something to do with the systemd-backlight service as outlined in the Save and restore functionality section of the Backlight Archwiki.

So SOMETHING is setting my brightness at boot, and it may be something that systemd-backlight succeeds at doing, and it precedes ACPI or Xorg because it is able to change the backlight when the system boots.

Here are some other notes about my system:

My display is LCD, not OLED, the 500-nit display for a Dell XPS 17 (9700). So this isn't a PWM thing.
My laptop graphics card is NVIDIA, with NVIDIA Optimus available configurations. There are a couple of configs I use, and both have the same behavior:
- This xorg.conf, with Optimus mode, putting X in the modesetting configuration using the low power Intel hardware
- This xorg.conf, with NVIDIA mode uses the nvidia driver and full-featured NVIDIA hardware.
I use systemd-boot in order to be able to add kernel parameters easily. Here's my /boot/loader/entries/arch.conf.

I've done quite a bit of fiddling, including methods of troubleshooting in the Backlight Archwiki and grepping on i915 and NVIDIA Optimus. There are lots of leads, and lots of references to systemd-backlight. I haven't actually run any systemd-backlight script because it doesn't seem clear to me that this is required, but I also don't quite understand it. If someone has a perspective or knowledge or really any feedback, please help me move forward!

Last edited by brandon.arnold (2021-02-27 23:59:31)

brandon.arnold · 2021-02-28 23:48:21

Due to no comments, I went ahead and reported the bug to kernel.org. Here's my bug report.

brandon.arnold · 2021-03-08 02:24:49

Update on this bug: I did a git bisect on the kernel, and found it was an i915 driver regression introduced by the intel-drm project. I posted my findings on a similar bug report here. Should get patched soon.

Maniaxx · 2021-03-08 15:47:46

nice.. thank you!

brandon.arnold · 2021-03-08 15:51:45

For my case (Dell XPS 17 9700), I was able to workaround by removing the kernel parameter `i915.enable_dpcd_backlight=1`. Keep track of the issue here, for Dell XPS 17 users.

Last edited by brandon.arnold (2021-03-08 23:44:27)

Arch Linux

#1 2021-02-06 10:58:26

Backlight/brightness controls stopped working

#2 2021-02-06 21:40:56

Re: Backlight/brightness controls stopped working

#3 2021-02-07 00:16:42

Re: Backlight/brightness controls stopped working

#4 2021-02-07 12:40:15

Re: Backlight/brightness controls stopped working

#5 2021-02-07 17:53:30

Re: Backlight/brightness controls stopped working

#6 2021-02-27 23:09:38

Re: Backlight/brightness controls stopped working

#7 2021-02-28 23:48:21

Re: Backlight/brightness controls stopped working

#8 2021-03-08 02:24:49

Re: Backlight/brightness controls stopped working

#9 2021-03-08 15:47:46

Re: Backlight/brightness controls stopped working

#10 2021-03-08 15:51:45

Re: Backlight/brightness controls stopped working

Board footer