/dev/backlight/backlight0: No such file or directory

teto91 · Monday at 9:49 PM

Hello, I am normally a Linux user, but I have an old Acer Aspire One which is an i386 and I found among the few OS that still supports it FreeBSD so I gave it a go.
I was able to make a dual boot FreeBSD/Windows XP.
I am currently running FeeBSD 13.5 with IceWM. Basically everything runs fine aside the brightness regulation which I really want to fix to save battery (and my eyes). Also the Fn keys do not work but I don't care I want to change brightness via command line.

This is the output of hw-probe: https://bsd-hardware.info/?probe=39030d3f23

I have installed the drm-kms and loaded the intel drivers, and I have read on the forum to try to load also the acpi_driver which I did but did not work.

My /boot/loader.conf:

Code:

acpi_asus_load="YES"
hw.i915kms.enable_dpcd_backlight=1
acpi_video_load="YES"
ubtbcmfw_load="YES"

and my /etc/rc.conf:

Code:

clear_tmp_enable="YES"
hostname="stefano-freebsd"
keymap="it.kbd"
wlans_ath0="wlan0"
ifconfig_wlan0="WPA DHCP"
sshd_enable="YES"
moused_enable="YES"
ntpdate_enable="YES"
ntpd_enable="YES"
powerd_enable="YES"
# Set dumpdev to "AUTO" to enable crash dumps, "NO" to disable
dumpdev="AUTO"
kld_list="i915kms cuse acpi_video"
lightdm_enable="NO"
ifconfig_re0="DHCP"
dbus_enable="YES"
slim_enable="YES"
webcamd_enable="YES"
webcamd_0_flags="-d ugen3.2"
wpa_gui_enable="YES"

However if I use backlight I get the following error:

Code:

backlight: cannot open /dev/backlight/backlight0: No such file or directory

(and it is true it does not exists at all the folder backlight).

This is the output of xrandr --verbose

Code:

Screen 0: minimum 1024 x 768, current 1024 x 768, maximum 1024 x 768
default connected 1024x768+0+0 (0x3ff) normal (normal) 0mm x 0mm
        Identifier: 0x3fe
        Timestamp:  120041
        Subpixel:   horizontal rgb
        Gamma:      1.0:1.0:1.0
        Brightness: 0.0
        Clones:  
        CRTC:       0
        CRTCs:      0
        Transform:  1.000000 0.000000 0.000000
                    0.000000 1.000000 0.000000
                    0.000000 0.000000 1.000000
                   filter:
        non-desktop: 0
                supported: 0, 1
  1024x768 (0x3ff)  0.000MHz *current
        h: width  1024 start    0 end    0 total 1024 skew    0 clock   0.00KHz
        v: height  768 start    0 end    0 total  768           clock   0.00Hz

As you can see the brightness is stuck to zero.

Of note on winXP I have no problem in changing the brightness with the Fn+left/right arrows key, so the hw is capable of it and it is working fine.

So I have a few questions:

why is backlight0 missing?
When is it supposed to be created?
During installation or at boot?
And why is it not created?
Is it an unsupported HW problem? A driver problem? A config problem?

/dev/backlight/backlight0: No such file or directory

teto91