xf86-video-ati update

I used the x11-drivers/xf86-video-ati-ums to use Xorg. My laptop is a little old (but it works ;) ) and my graphics card is an ATI Radeon HD4570.
With this package I can use ClockGating and DynamicPM so my card doesn't overheat.
After xorg update I should replace the ums driver to the "normal" x11-drivers/xf86-video-ati and I can't use dynamic power management. And now the fans try to cooling (switch on about 10 seconds, switch off and switch on again). It's annoying.
Is there any solution to force low power mode?