https://bugs.freedesktop.org/show_bug.cgi?id=106228
Bug ID: 106228 Summary: amdgpu reads back brightness 0 (which is not true) if checked before a brightness has been explicitly set Product: DRI Version: unspecified Hardware: Other OS: Linux (All) Status: NEW Severity: normal Priority: medium Component: DRM/AMDgpu Assignee: dri-devel@lists.freedesktop.org Reporter: jian-hong@endlessm.com
Created attachment 139091 --> https://bugs.freedesktop.org/attachment.cgi?id=139091&action=edit The full dmesg
I have tried to install Linux OS on ASUS laptop which is equipped with AMD Ryzen 5 2500U with Radeon Vega Mobile Gfx.
When the Linux installation completed and entered to the OS, the brightness of display looks normal but the brightness bar is shown as the lowest level within the display's brightness GUI setting.
Also check "cat /sys/class/backlight/amdgpu_bl0/brightness" and it is 0.
After a system reboot, Brightness is dimmed to the lowest level. Check "cat /sys/class/backlight/amdgpu_bl0/brightness" again and it is 12.
To make sure it is the problem that "system always reads back brightness 0 if checked before a brightness has been explicitly set". I disable all of the brightness setting applications, including masking systemd-backlight service and than reboot. "cat /sys/class/backlight/amdgpu_bl0/brightness" before set brightness manually again and it reads back 0, but the brightness of display looks normal actually. Then, if I drag the brightness bar in GUI, the actual brightness changes and the "/sys/class/backlight/amdgpu_bl0/brightness" goes to the right value. And, I reboot again, then the same things happen again.
I also tried this with kernel v4.17.0-rc2. It still has the same problem.