As of the 3.9 kernel, the gma500 driver now properly supports setting the screen brightness, and the brightness keys work as intended, with one exception: The brightness is maxed out at 80. I can set the brightness to 100 (The actual maximum) by writing to sys/class/backlight/psb-bl/brightness, as normal, but the actual brightness+ key won't raise it over 80. In a possibly unrelated issue, disconnecting or connecting the AC adapter causes the brightness level to reset to 80, if it is higher than 80.
Hi Bruno Since changing screen brightness now "works" it has made other problems visible. This is something I'm gonna look into. I also have issues with setting the backlight from things like Unity and getting the wrong level after DPMS off/on and after suspend/resume. I'll get back to you when I've had a chance to look at it. Thanks Patrik
Thanks for the response, Patrik To keep you up to date - I am now on kernel version 3.9.4 and this problem persists, and I've also been noticing brightness levels being wrong after suspend/resume. I'm curious about you mentioning Unity - have you been able to get Unity to a usable state under the gma500_gfx driver at all? Anything that leans heavily on OpenGL acceleration (Gnome shell 3 and Cinnamon for example) is unusably slow for me with this driver. Thanks again, Bruno
As for Unity, it's totally useless for me as well, but I include it in my testings. I almost have a working DDX with EXA so hopefully there will be the possibility for 2D accelerated X in 3.11 or 3.12. It might not be enough for compositing WM's but will help LXDE and friends.
FYI, if the hotkeys work through acpi, they respect the brightness levels from BIOS. This means there's a fixed set of levels, the lowest of which may not be 0%, and the highest may not be 100%. Disclaimer: I don't know how any of this works in gma500.
Then that is probably the reason for the 80% cap. It looks to me that the brightness is set twice (BIOS and driver) so that could be the problem for the other issues that I'm getting. Still on the todo-list though.