nvidia - Can't set screen brightness in Gentoo system

My system:

Linux gentoo 3.10.7-gentoo-r1
VGA compatible controller: NVIDIA Corporation GT216M [GeForce GT 240M] (rev a2)

output of xbacklight: No outputs have backlight property

output of xrandr:

xrandr: Failed to get size of gamma for output default
Screen 0: minimum 640 x 480, current 1280 x 720, maximum 1280 x 768
default connected 1280x720+0+0 0mm x 0mm
   1280x720        0.0* 
   1024x768       61.0  
   800x600        61.0  
   640x480        60.0  
   1280x768        0.0 

output of ls /proc/acpi:

button/ event

When I'm in kernel 3.8.13, I can change my brightness using xbacklight. I compiled 3.10.7-r1 using genkernel all. Before the upgrade I did get a notice of "compatible issues for Nvdia users" from emerge but I still don't know the details.

It there anyway to let me set the brightness?

Then i found a ebuild app-laptop/nvdiabl-0.81 and tried to emerege nvidabl, I got this message:

Your kernel does not support FB_BACKLIGHT. To enable you it you can enable any frame buffer with backlight control or nouveau. Note that you cannot use FB_NVIDIA with nvidia's proprietary driver Please check to make sure these options are set correctly. Failure to do so may cause unexpected problems. Once you have satisfied these options, please try merging this package again. ERROR: app-laptop/nvidiabl-0.81::gentoo failed (pretend phase): Incorrect kernel configuration options

Call stack: ebuild.sh, line 93: Called pkg_pretend nvidiabl-0.81.ebuild, line 31: Called linux-mod_pkg_setup linux-mod.eclass, line 559: Called linux-info_pkg_setup linux-info.eclass, line 911: Called check_extra_config linux-info.eclass, line 805: Called die The specific snippet of code: die "Incorrect kernel configuration options"

[SOLVED] I enter the menuconfig again and check the Device Drivers -> Graphics support -> Support for frame buffer devices, then i found this:

<*> nVidia Framebuffer Support
[*] Support for backlight control (NEW)

What can i say. Recompiling...