Bug#942219: systemd-backlight at backlight:dell_backlight.service fails at boot for dell d600, d620, d820

[Michael Biebl]

On 15.10.19 03:03, Rado S wrote:
> =- Michael Biebl wrote on Mon 14.Oct'19 at 23:20:57 +0200 -=
> 
>> Am 14.10.19 um 23:13 schrieb Rado S:
>>> dell_backlight: Failed to write system 'brightness' attribute: No such device or address
>>
>> Looks like a kernel or firmware/bios problem to me.
>>
>> Since you didn't use reportbug there is no information about your used
>> kernel.
> 
> It is in the journalctl output;
> Linux version 4.19.0-6-686-pae (debian-kernel at lists.debian.org) (gcc version 8.3.0 (Debian 8.3.0-6)) #1 SMP Debian 4.19.67-2 (2019-08-28)
> 
> The dell d600 (also failing) uses the non-pae version of it.
> The functioning vostro uses the same pae-version.
> 
> What more information can I provide?
> 

It appears you have backlight device without a brightness attribute.
Here this look like this

> # ls -la /sys/class/backlight/intel_backlight/
> insgesamt 0
> drwxr-xr-x 3 root root    0 Okt 15 13:29 ./
> drwxr-xr-x 4 root root    0 Okt 15 01:15 ../
> -r--r--r-- 1 root root 4096 Okt 15 13:27 actual_brightness
> -rw-r--r-- 1 root root 4096 Okt 15 13:27 bl_power
> -rw-r--r-- 1 root root 4096 Okt 15 13:28 brightness
> lrwxrwxrwx 1 root root    0 Okt 15 13:27 device -> ../../card0-LVDS-1/
> -r--r--r-- 1 root root 4096 Okt 15 01:15 max_brightness
> drwxr-xr-x 2 root root    0 Okt 15 13:27 power/
> lrwxrwxrwx 1 root root    0 Okt 15 01:15 subsystem -> ../../../../../../../class/backlight/
> -r--r--r-- 1 root root 4096 Okt 15 01:15 type
> -rw-r--r-- 1 root root 4096 Okt 15 01:15 uevent

I can get the current brightness via
> # cat /sys/class/backlight/intel_backlight/brightness
> 1500

and change it via
> # echo 2000 > /sys/class/backlight/intel_backlight/brightness

What's the output you get for your dell_backlight?

-- 
Why is it that all of the instruments seeking intelligent life in the
universe are pointed away from Earth?

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