doesn't work on 4.4, but works on 3.10.32

[imz]

I have a problem on linux 4.4.119, but not on linux 3.10.32:

smbios-lcd-brightness --value=1

has a visible effect on linux 3.10.32, but not on linux 4.4.119, though the saved value is modified indeed.

Do you have some ideas?

python-module-smbios-2.3.3-alt1.0.g4fec2ad.noarch
libsmbios-2.3.3-alt1.0.g4fec2ad.x86_64
smbios-utils-2.3.3-alt1.0.g4fec2ad.x86_64

Dell Latitude 6430u

[imz]

See also https://bugs.launchpad.net/altlinux/+source/libsmbios/+bug/331357

[imz]

The situation was the same with older libsmbios-2.2.28-alt1.1

[imz]

It runs like this (but there is no effect):

[root@ovicaa ~]# smbios-lcd-brightness --value=15
Reading current Battery mode setting
    current: 1
        min: 0
        max: 15
Write new Battery mode setting
Reading current Battery mode setting
    current: 15
        min: 0
        max: 15
[root@ovicaa ~]# smbios-lcd-brightness --value=1
Reading current Battery mode setting
    current: 15
        min: 0
        max: 15
Write new Battery mode setting
Reading current Battery mode setting
    current: 1
        min: 0
        max: 15
[root@ovicaa ~]# 

[superm1]

I would suspect it's related to:

1. The built-in handling from the dell-laptop kernel driver.
   or
2. A move to intel graphics driver handling brightness instead

[imz]

Yes, thanks for the ideas. Perhaps, it's the video driver which can control this now. (Whose "move" has this been? Doesn't dcdbas and smbios work on its own?)

 cat /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/max_brightness > /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness

now makes it bright, and

 echo 0 > /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness

makes it non-bright.

[superm1]

I would definitely recommend using that interface instead. It means that there doesn't have to be a SMI invoked in order to accomplish changing the backlight. You'll have better performance this way.

[imz]

On 3.10.32, there were 3 interfaces and all worked. (Now, I could remember that I tried them all a long time ago and selected smbios as my choice.)

They all work, i.e., have a visible effect. Their values are in different units. Their values affect each other, but in a funny way:

• Setting through smbios-lcd-brightness affects /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness, but not /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness:

[root@ovicaa ~]# cat /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness; cat /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness; smbios-lcd-brightness 
976
100
Reading current Battery mode setting
    current: 15
        min: 0
        max: 15
[root@ovicaa ~]# smbios-lcd-brightness --value=1
Reading current Battery mode setting
    current: 15
        min: 0
        max: 15
Write new Battery mode setting
Reading current Battery mode setting
    current: 1
        min: 0
        max: 15
[root@ovicaa ~]# cat /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness; cat /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness; smbios-lcd-brightness 
168
100
Reading current Battery mode setting
    current: 1
        min: 0
        max: 15
[root@ovicaa ~]# 

• Setting /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness affects /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness and the value reported by smbios-lcd-brightness:

[root@ovicaa ~]# cat /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness; cat /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness; smbios-lcd-brightness 
976
100
Reading current Battery mode setting
    current: 15
        min: 0
        max: 15
[root@ovicaa ~]# echo 0 > /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness
[root@ovicaa ~]# cat /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness; cat /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness; smbios-lcd-brightness 
168
0
Reading current Battery mode setting
    current: 1
        min: 0
        max: 15
[root@ovicaa ~]# 

• Setting /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness doesn't affect other values:

[root@ovicaa ~]# cat /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness; cat /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness; smbios-lcd-brightness 
976
100
Reading current Battery mode setting
    current: 15
        min: 0
        max: 15
[root@ovicaa ~]# echo 168 > /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness
[root@ovicaa ~]# cat /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness; cat /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness; smbios-lcd-brightness 
168
100
Reading current Battery mode setting
    current: 15
        min: 0
        max: 15
[root@ovicaa ~]# 

So, it seems for /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness to have been the best place to set the value so that all reported values are consistent.

However, in linux 4.4, there is no /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness.

[superm1]

That's a pretty peculiar combination. I would recommend to just stick with the intel one.