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#1 2021-07-01 09:50:50

Drorago
Member
Registered: 2021-07-01
Posts: 8

unable to control the backlight

Hello,
My on my laptop, an HP omen 15-ceo47nf, I'm not able to adjust the backlight.

The computer have hybrid graphics provided by an Intel Core i5-7300HQ  and an nvidia GTX 1060 mobile 6GB.
when I start x then kill it the tty is brighter but it does not affect x servers.

I already tried to use xbacklight, light, and changing the value of '/sys/class/backlight/nvidia_0/brightness' and even if the value change it has no effect on the backlight.
I also try to add this option in the device section of '/etc/xorg.conf' but it has no effect:

Option "RegistryDwords" "EnableBrightnessControl=1"

I have this warning in the Xorg log but I have no clue of wat to do whith it:

[   827.271] (WW) VGA arbiter: cannot open kernel arbiter, no multi-card support

I don't know what did I have to look for to fix the issue so any help is welcome.
thank you in advance for your help.

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#2 2021-07-05 10:58:53

rep_movsd
Member
Registered: 2013-08-24
Posts: 84

Re: unable to control the backlight

Try adding

acpi_backlight=vendor

to your kernel boot command line

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#3 2021-07-06 04:51:24

Drorago
Member
Registered: 2021-07-01
Posts: 8

Re: unable to control the backlight

It has no effect.

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#4 2021-07-06 14:19:36

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 17,848

Re: unable to control the backlight

What is the output of  ls -l /sys/class/backlight/*/


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
---
How to Ask Questions the Smart Way

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#5 2021-07-06 14:23:06

Drorago
Member
Registered: 2021-07-01
Posts: 8

Re: unable to control the backlight

total 0
-r--r--r-- 1 root root  4096 Jul  6 16:20 actual_brightness
-rw-r--r-- 1 root root  4096 Jul  6 16:20 bl_power
-rw-rw-r-- 1 root video 4096 Jul  6 06:48 brightness
lrwxrwxrwx 1 root root     0 Jul  6 16:20 device -> ../../../0000:01:00.0
-r--r--r-- 1 root root  4096 Jul  6 16:20 max_brightness
drwxr-xr-x 2 root root     0 Jul  6 16:20 power
-r--r--r-- 1 root root  4096 Jul  6 16:20 scale
lrwxrwxrwx 1 root root     0 Jul  6 16:20 subsystem -> ../../../../../../class/backlight
-r--r--r-- 1 root root  4096 Jul  6 16:20 type
-rw-r--r-- 1 root root  4096 Jul  6 16:20 uevent

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#6 2021-07-06 14:28:04

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 17,848

Re: unable to control the backlight

Looks good.  Now the output of
ls /sys/class/backlight
cat /sys/class/backlight/*/max_brightness
and
cat /sys/class/backlight/*/*brightness


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
---
How to Ask Questions the Smart Way

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#7 2021-07-06 14:30:36

Drorago
Member
Registered: 2021-07-01
Posts: 8

Re: unable to control the backlight

ls /sys/class/backlight

nvidia_0

cat /sys/class/backlight/*/max_brightness

100

cat /sys/class/backlight/*/*brightness

100
100
100

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#8 2021-07-06 14:51:08

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 17,848

Re: unable to control the backlight

Opps, I had an extra * in there.  But, no matter, it works smile

Assuming your user is in the wheel group, lets try sudo bash -c "echo 50 > /cat/sys/class/backlight/*/brightness"

I hope that changes the brightness.  If not, post any errors from that command and cat /sys/class/backlight/*/*brightness again


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
---
How to Ask Questions the Smart Way

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#9 2021-07-06 15:02:31

Drorago
Member
Registered: 2021-07-01
Posts: 8

Re: unable to control the backlight

I tried:

sudo bash -c "echo 50 > /cat/sys/class/backlight/*/brightness"

but ther is no /cat folder
I think you wanna me to use

 sudo bash -c "echo 50 > /sys/class/backlight/*/brightness" 

and it dosen't change the brightness.

cat /sys/class/backlight/*/*brightness:

50
50
100

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#10 2021-07-06 15:03:57

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 17,848

Re: unable to control the backlight

Clearly I need more coffee this morning

sudo bash -c "echo 50 >  cat /sys/class/backlight/*/brightness"


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
---
How to Ask Questions the Smart Way

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#11 2021-07-06 15:05:50

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 17,848

Re: unable to control the backlight

Well, that shows the command was accepted.   Is this with or without the suggestion of rep_movsd for the command line option ?

Last edited by ewaller (2021-07-06 15:06:29)


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
---
How to Ask Questions the Smart Way

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#12 2021-07-06 15:18:56

Drorago
Member
Registered: 2021-07-01
Posts: 8

Re: unable to control the backlight

it was without the command line option. I reboot with and retry

 sudo bash -c "echo 50 >  cat /sys/class/backlight/*/brightness" 

but it has no effects on the brightness and doesn't change the values I get when I do

cat /sys/class/backlight/*/*brightness

100
100
100

. I retried

 sudo bash -c "echo 50 > /sys/class/backlight/*/brightness"  

and it doesn't  change the brightness but it change the values:

 cat /sys/class/backlight/*/*brightness                      
50
50
100

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#13 2021-07-06 15:52:05

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 17,848

Re: unable to control the backlight

It would appear that the backlight has some other means of controlling it on this laptop.  I am puzzled why there is no structure for intel_backlight under /sys/class/backlight

Can we try this again after rebooting with the kernel command line option acpi_backlight=native
?


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
---
How to Ask Questions the Smart Way

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#14 2021-07-06 15:58:01

Drorago
Member
Registered: 2021-07-01
Posts: 8

Re: unable to control the backlight

It is the same as with acpi_backlight=vendor.

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#15 2021-07-06 15:59:24

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 17,848

Re: unable to control the backlight

As a sanity check, what is the output of cat /proc/cmdline
?


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
---
How to Ask Questions the Smart Way

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#16 2021-07-06 16:03:50

Drorago
Member
Registered: 2021-07-01
Posts: 8

Re: unable to control the backlight

cat /proc/cmdline 

BOOT_IMAGE=/boot/vmlinuz-linux root=UUID=81c5d39f-d8ef-4677-be87-9efc8c82dba4 rw loglevel=3 quiet acpi_backlight=native

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