On Tue, 5 Apr 2022 davidson wrote:
On Mon, 4 Apr 2022 Juan R.D. Silva wrote:On 2022-04-04 5:17 a.m., davidson wrote:On Sun, 3 Apr 2022 Juan R.D. Silva wrote:Hi folks,Debian 11 on Dell M4800 Mobile Workstation with Nvidia Quadro K2100M card.I've been using the system with full (100%) screen brightness for rather long time. Today I wanted to reduce it and to my astonishment found that GNOME "progressed" to the point when even this basic feature has gone.The function keys work, the sliders move. Everything is dandy, except it has no effect on the actual brightness, which stack at 100%. Even setting the brightness in BIOS to 50% instead of 100% has no effect.
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I'll show you what I do. I don't use GNOME, but maybe it will work. Four steps: 1. Confirm this directory has expected contents: $ ls -p /sys/class/backlight/acpi_video0/actual_brightness bl_power brightness device max_brightness power/ subsystem type ueventIt has "brightness" and "max_brightness" files. So far so good. 2. Find out what counts as maximum brightness. (I think I have seen this vary from laptop to laptop): $ cat /sys/class/backlight/acpi_video0/max_brightness 7 3. Find out what value current brightness is: $ cat /sys/class/backlight/acpi_video0/brightness 5 4. As root, write some value less-than-or-equal-to maximum brightness (found in step 2) into "brightness" file. For example, when 5 is too bright, I might try replacing that with 4. # echo -n 4 > /sys/class/backlight/acpi_video0/brightness
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All 4 steps are correct. And I most certainly can happily change the value in the /sys/class/backlight/acpi_video0/brightness file to whatever I want. The problem is it does not have any effect on the actual/physical screen brightness.
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In the mean time, out of curiosity I searched for terms /sys/class/backlight/acpi_video0/brightness ineffective and got some results that were informative to me (in my infinite ignorance). The question in this one was interesting, https://askubuntu.com/questions/1045624/how-to-switch-between-options-in-sys-class-backlight-to-solve-brightness-prob ...because it looks to me that the questioner has the same symptoms as you, but *can* manipulate screen brightness using /sys/class/backlight/nv_backlight/* files instead. This made me wonder if you have a directory /sys/class/backlight/nv_backlight/
What does... $ ls -l /sys/class/backlight/ ... say?
If you do, you could try the same four ineffective steps as before, except replace "acpi_video0" with "nv_backlight".