No brightness control after sleep

Hello all.

Does somebody know how to fix the “no brightness control after sleep” issue?

Any time after booting the system, I can control the screen backlight with the Fn keys; but if I put the computer to sleep and I wake it up, then the Fn+brightness keys don’t work any more. I see the pop-up brightness indicator moving up and down, but the backlight remains with no change. However, I still can control it issuing a command of the type “echo 500 > /sys/class/intel_backlight/brightness”. It’s only the Fn+bright keys which don’t work after resuming from suspend.

I’ve tried with kernels 3.5.3 and 3.6.7, to no avail. I don’t think it’s a desktop-manager related problem, because I’ve tried with KDE and with XFCE, but same results. I’ve also tried using the kernel boot option “acpi_backlight=vendor”, which used to be the “known fix” for this issue (and actually works with my parallel Kubuntu 12.05), but it doesn’t work with CL. I’ve tried installing laptop-mode-tools, but to no avail either.

Any clue? Some hint? How can I try to debug? When I check /var/log, I can’t see any system log from where to gather some useful information…

My system has an Intel Sandy Bridge chip / graphics card. The driver is i915.

In the evening i’ll check and try to find a solution to this problem on my laptop with intel graphic card.

Thx! If I can help with some information, I’ll be glad to.