I have a Vaio S13 laptop with a Nvidia 310M graphics card. For some time now I have been having a recurring problem with the brightness controls. Besides the need to edit /etc/X11/xorg.conf and adding EnableBrightnessControl=1 to enable brightness control keys, sometimes (completely sporadically, still trying to find a way to reproduce it) brightness controls are very laggy and unresposive (needs 2 or more key strokes to respond). This really gets on my nerves as it is difficult to get a specific brightness level.
As I said, I still have not found when exactly does this happens and how to reproduce it, however it seems to have something to do with power management, as it often starts on the boot after changing from AC power to battery or vice-versa. If I keep it always on AC, brightness control keys are very responsive.
I've already tried adding a 15-nvidia.conf to /usr/share/X11/xorg.conf.d/ with the "device" settings and deleting /etc/X11/xorg.conf, but that only deteriorates the laggy behaviour when it happens. Adding acpi_backlight=vendor to the kernel parameters completely disables brightness controls.
This happens in both Ubuntu and Arch, so I am think it is somehow kernel-related. So, does anyone has a similar problem and knows a fix? Any insight on this is useful, I'm lost here...
Still can't make sense of this issue. I've realized that since Gnome shell added the brightness control daemon, I've able to control brightness through there. Additionally, after a suspend brightness controls seem to be working, though rarely ever with a cold reboot...