[solved][Wayland] backlight control

[dark raven]

Each time I start a wayland compositor (any), the brightness seems to reset until I press brightness control keys on my laptop keyboard. I also noticed that utilities like brightnessctl are able to change backlight brightness, but it doesn't get notified of change, and stays at old brightness until you change it using keyboard controls

also, turning on/off screen resets brightness too

which also means suspend will make it reset

[azure basin]

Can you do auditctl -w /sys/class/backlight and then post the journalctl log after starting a wayland compositor?

[azure basin]

Start auditd.service before the auditctl command.

[azure basin]

Use

 journalctl -b0 -t audit | curl -F 'f:1=<-' ix.io

to upload the log

[dark raven]

-- No entries --

[azure basin]

try

journalctl -b0 --grep='audit:' | curl -F 'f:1=<-' ix.io

[dark raven]

http://ix.io/4ATy

I ran wayland compositor after the commands, ran brightnessctl, and also changed brightness using keys

clearly the logs don't have that info

[azure basin]

No, user space changes the brightness via /sys/class/backlight, and the kernel audit firmware should capture that with this particular audit rule, which basically logs any access to that path.

Maybe the rule wasn't created or deleted, or the log is somewhere else.

@dark raven
What is the output of

auditctl -l

And what is the output of

grep log_file /etc/audit/auditd.conf

[dark raven]

with sudo, right?

[azure basin]

All commands should be run as root in this context, unless otherwise specified.

[dark raven]

-w /sys/class/backlight -p rxwa
-w /sys/class/backlight/acpi_video0 -p rxwa

[azure basin]

grep log_file /etc/audit/auditd.conf

[dark raven]

max_log_file = 8
max_log_file_action = ROTATE

[azure basin]

sudo find /sys -name actual_brightness -exec  auditctl -w {} \;

[dark raven]

yeah btw there is no actual_brightness file in /sys/class/backlight/acpi_video0

[azure basin]

So what is the output of sudo find /sys -name actual_brightness

And what is in /sys/class/backlight/acpi_video0?

[azure basin]

Can you try to find audit logs in dmesg

[dark raven]

/sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/actual_brightness

[azure basin]

Your words contradict themselves

[dark raven]

wdym

[azure basin]

/sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/actual_brightness
There are actual_brightness in acpi_video0

[dark raven]

wtf

now there is

[azure basin]

Can you post the output from

ls /sys/class/backlight/acpi_video0  
findmnt /sys/class/backlight

[dark raven]

actual_brightness bl_power brightness device max_brightness power scale subsystem type uevent

second one nothing

[azure basin]

Ok, could you please try to see if there are any audit logs in dmesg?

[dark raven]

how should they look

I don't think there are

[azure basin]

Would you kindly upload them with

sudo dmesg | gzip | curl -F 'f:1=<-' ix.io

[dark raven]

http://ix.io/4ATF

So I was looking it up online and even echo $level > /sys/class/backlight/acpi_video0/brightness has no effect until I use keyboard keys

[azure basin]

Alright, there is no audit log, maybe the kernel parameters have disabled it.
What is in /sys/class/backlight?

ls /sys/class/backlight

[dark raven]

just acpi_video0

[azure basin]

lspci -k | curl -F 'f:1=<-' ix.io

[dark raven]

4ATM

[azure basin]

What is your CPU and GPU?

[dark raven]

Intel Celeron U3400

and igpu is listed as Intel Core Processor lol

[azure basin]

There has been a change in the kernel backlight stack that favours ACPI baclight management over vendor specific.

When did you first notice this problem?

[dark raven]

Ever since I installed linux on this trashtop

There's a script on archwiki

#!/bin/sh

path=/sys/class/backlight/acpi_video0

luminance() {
    read -r level < "$path"/actual_brightness
    factor=$((100 / max))
    printf '%d\n' "$((level * factor))"
}

read -r max < "$path"/max_brightness

xbacklight -set "$(luminance)"

inotifywait -me modify --format '' "$path"/actual_brightness | while read; do
    xbacklight -set "$(luminance)"
done

You think it could work?

[azure basin]

It doesn't work with modesetting, which Wayland requires.

[dark raven]

Can you explain what modesetting? I don't really understand what you're talking about

[azure basin]

a method for setting display resolution and depth in the kernel space rather than user space

[azure basin]

can you cat /proc/cmdline

[dark raven]

BOOT_IMAGE=../vmalinuz-linux root=/dev/sda3 rw resume=/dev/sda4 initrd../initramfs-linux.img

Sorry it's taking too long to respond, I'm just typing from desktop, and I can't copy text easily, and I'm also going afk to do some things at home

[azure basin]

Can you try the kernel parameter acpi_backlight=video?

sudo kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --command-line="root=/dev/sda3 rw resume=/dev/sda4 acpi_backlight=video"
sudo systemctl kexec

[dark raven]

What is this command? Can I just add kernel param to bootloader config and reboot?

[azure basin]

Well, kexec should be faster, and there are another 2 parameters that need to be tested separately.

[azure basin]

After reboot, can you find this directory /sys/class/backlight/intel_backlight?

[dark raven]

nope

still acpi_video0

[azure basin]

sudo kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --command-line="root=/dev/sda3 rw resume=/dev/sda4 acpi_backlight=vendor"
sudo systemctl kexec

• note: changed acpi_backlight from video to vendor

[dark raven]

kexec not found

what package is it in?

[azure basin]

kexec-tools

[dark raven]

yoooo

[azure basin]

First try

sudo kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --command-line="root=/dev/sda3 rw resume=/dev/sda4 acpi_backlight=video"
sudo systemctl kexec

Then

sudo kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --command-line="root=/dev/sda3 rw resume=/dev/sda4 acpi_backlight=vendor"
sudo systemctl kexec

Finaly

sudo kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --command-line="root=/dev/sda3 rw resume=/dev/sda4 acpi_backlight=native"
sudo systemctl kexec

After each reboot see if there is a path /sys/class/backlight/intel_backlight0 or anything that is not acpi_video0

[dark raven]

there's now acer-wmi

[dark raven]

that's with vendor

[azure basin]

Can you ls it

[dark raven]

yeah, contents as in acpi_video0

actual_brightness bl_power, etc

[azure basin]

Does echo some_number > /sys/class/backlight/acer-wmi/brightness change the screen brightness

[dark raven]

although changing brightness via brightnessctl has no effect now

[dark raven]

I assume brightnessctl already did that

[azure basin]

Can you try it

brightnessctl only select one backlight device if there are several.

[dark raven]

no effect with echo too

[dark raven]

there is one though, and the output did mention it's acer_wmi

[azure basin]

Can you try this?

sudo kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --command-line="root=/dev/sda3 rw resume=/dev/sda4 acpi_backlight=native"
sudo systemctl kexec

[dark raven]

intel_backlight now

It works!!!!!!!

Thank you

[solved][Wayland] backlight control

[azure basin]

Is the Wayland Composer problem also solved?

[dark raven]

yeah I tried brightnessctl within the compositor

[azure basin]

So no more

the brightness seems to reset until I press brightness control keys on my laptop keyboard
?

[dark raven]

the reset, idk, lemme try

yeah

solved too

What's funny is that I can set it to be even darker than I previously could

[azure basin]

The kernel parameter acpi_backlight=native set by kexec is not permanent. It needs to be set in a config file

[dark raven]

I understand, yeah

I will modify syslinux cfg

[azure basin]

May you kindly extend a helping hand to those in need, if and when you can.

Have a nice day