Solved Nvidia backlight control

aragats

Daemon

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Exploring a new Dell Precision 7540 with Nvidia Quadro RTX3000: I can't find any way to control the display backlight brightness other that by running x11/nvidia-settings:
Code:
nvidia-settings -a BacklightBrightness=x    # x = 0...100
This is good for desktop use with Xorg, but doesn't work for console. Moreover, if I run it from console when X server is running, it doesn't work either, although doesn't report any error ― just silently exits (obviously $DISPLAY is set).

In Linux there is a corresponding entry in /sys, thus I can easily echo values in it. In FreeBSD I would expect a possibility with sysctl, but that's not the case. Mounting linsysfs doesn't help either.

Thanks for ideas!
 
OP
aragats

aragats

Daemon

Reaction score: 709
Messages: 1,630

have you tried loading acpi_video(4)
I haven't, thanks for the idea, I forgot about it.
I haven't since am 99% sure it won't work at least because of Precision's buggy BIOS which is reported by Linux users, and I've seen a flood of messages with ACPI errors every time when brightness keys are pressed in Linux. So in Linux I had to bind those keys to a script echoing values into the /sys/.../brightness entry.
It's worth trying anyway.
 
OP
aragats

aragats

Daemon

Reaction score: 709
Messages: 1,630

Cool! After loading acpi_wmi() and acpi_video() the backlight control works with the corresponding keys!
In contrast to Linux, the ACPI errors messages appear just once ― without flooding dmesg().

Just today Dell released a BIOS update, hopefully it will have fixes. The funny thing is that the backlight control doesn't work even on the BIOS setup page with their own sliders! Although, it works when the "switchable graphics" is enabled ― the laptop has both Intel and Nvidia cards, but the BIOS page clearly states that option can be used only with latest Windows and Ubuntu.
 
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