When brightness hotkeys are operated at a normal rate of multiple key presses per second, the brightness control snaps to 0 on second or third keypress. The brightness OSD suddenly displays 0 value and the screen dims. When waiting for 2 or more seconds between key presses, the brightness control appears to operate normally. The actual brightness of the screen lags behind the setting and changes brightness gradually within about a second, which is normal and expected on this machine and has been seen on other DE and other OS. However it seems that when brightness not fully changed yet, the XFCE power manager or something down the line misbehaves and forces zero brightness instead. $ xfce4-power-manager -V Xfce Power Manager 1.4.4 $ uname -a Linux xxxxxx 4.4.0-66-generic #87-Ubuntu SMP Fri Mar 3 15:29:05 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux /sys/class/backlight/ideapad $ cat max_brightness 16 Distribution: Linux Mint 18.1 featuring XFCE 4.12
Reproduced the issue by compiling git 755a515. Immediately after new brightness is set with xrandr, xfpm_brightness_xrandr_get_level occasionally returns *current=0! No warning is output, ret=TRUE. How do i proceed troubleshooting the issue? It looks approximately like this, debug statements added by me: ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_up: max_level=16, set_level=14 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_set_level: level=14 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_get_level: ret=1, current=14, actual_type=19, nitems=1, actual_format=32 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_get_level: ret=1, current=14, actual_type=19, nitems=1, actual_format=32 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_up: max_level=16, set_level=15 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_set_level: level=15 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_get_level: ret=1, current=0, actual_type=19, nitems=1, actual_format=32 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_get_level: ret=1, current=0, actual_type=19, nitems=1, actual_format=32 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_up: max_level=16, set_level=1 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_set_level: level=1 ** (xfce4-power-manager:22116): DEBUG: xfpm_brightness_xrandr_get_level: ret=1, current=1, actual_type=19, nitems=1, actual_format=32
Hello? Anybody there? I think i'm speaking into the void. It appears my issue is two different things, broken XrandR backlight, which goes away with intel to modeset transition that is happening now in xorg anyway, and helper priority routines which have already been fixed by git 36b2c96.
It is not a bug in xfce power manager, your driver is sending back 0 as brightness for some reason...