Debian Jessie 8 issues with brightness not working.
Debian Jessie 8 issues with brightness not working.
I encountered the same problem on my Acer laptop with an Intel processor. The solution was simple: open /etc/default/grub with gedit (or another editor), locate the line GRUB_CMDLINE_LINUX_DEFAULT and change it to quiet splash acpi_backlight=vendor. Save the file and close the editor. Next, run the update-grub command in the terminal and reboot your system. Let me know if it works!
I now possess this updated linked directory /sys/class/backlight/asus-nb-wmi. To create an xorg.conf file and test functionality. The section "Device" Identifier is set to "0x17a", with the driver labeled "asus-nb-wmi". The option "Backlight" points to "asus-nb-wmi". EndSection The driver was uncertain about what to include since existing information online didn't meet expectations, though it had previously worked with a Radeon setup which led to issues with the Light Display Module.
The update led to the desktop failing to load and redirected me to the console. I undid the change by removing the xorg.conf file I created. Still, adjusting brightness remains impossible. The system reported a default gamma size of zero, and attempts to set brightness via various commands either failed or reset to zero. Further details were found in the backlight directory and a recent edit log.
Avoid any X.org related actions. Ignore other Xorg configurations. Test ACPI methods as well, using acpi_backlight=native as an option. You can also try the following steps: update-grub and reboot to ensure the driver is loaded. Checking lsmod | grep amdgpu and lsmod | grep radeon helps confirm the setup.
I think you mentioned reading from the ArchWiki article already, right? Here are the findings, as requested: acpi_backlight=vendor was set in my previous reply, which created a new symlink to the asus-nb-wmi folder. Then acpi_backlight=native removed it without altering anything else. acpi_backlight=none just performed a native operation. Each time I rebooted, I adjusted brightness using xrandr commands with different values and also tried xbacklight -set 10, pressing fn + f5/f6 manually, plus changing the file in /sys/class/backlight/. Regarding the kernel module, I double-checked it appears in lsmod for both "asus-wmi" and "asus-nb-wmi". I've been using Linux since 2010 and know enough to navigate the system effectively. The Udev rule didn't help because my brightness max is 0, while the current level is -19. Changing it doesn't affect it unless you use udev, which still leaves it at -19. I've tried restarting multiple times (up to 8) without success, adjusting values from -20 to -42, but none fixed it. The lsmod and radeon entries in the kernel list returned nothing. I also installed xserver-xorg-video-amdgpu and followed a guide on the Debian Wiki, yet I still don't understand what's malfunctioning or where to look.
This might be the problem. Avoid modifying udev rules—they aren't required on Debian and won't help with this issue. Stick to modprobe instead of insmoding drivers. Make sure you're not encountering "unknown symbol" errors. Try adding "contrib non-free" to sources.list to see if the packages appear. After that, rerun lsmod as before. What GPU model is it?
I previously installed linux-firmware-nonfree, choosing non-free packages during Debian installation and adding it manually to the repos. A9 AMD appears on ASUS's store listing as AMD R5 M420. I deleted the udev rule, and lsmod doesn't include amdgpu or radeon.
Work is finished now that the required Debian 8 is installed. I can resume adjusting settings to address the brightness problem. The command failed to display the radeon driver, but lsmod | grep radeon returned several entries. Restarting should trigger the driver update process. After rebooting, I checked the module list and confirmed the radeon module was removed, which explains why modprobe didn't persist it. The xorg log was saved after reboot and shows no changes in brightness settings.
It might actually be newer than I realized... Especially for Debian, an unupdated kernel could be the real problem. You're likely using a fallback VESA driver, and your current Radeon driver probably isn't compatible. It's unclear if there are straightforward ways to upgrade the kernel, but as a last option, you could try the latest release or boot from a live USB distribution like Manjaro, which offers modern software for testing drivers.
If the Radeon driver fails after rebooting, it suggests the support is missing. You might need to manually add Radeon to /etc/modules-load.d/modules.conf, though this could cause issues.
Edited January 15, 2019 by Guest