Since Linux Kernel 3.11, the open source AMD Radeon driver got dynamic power management (DPM) feature support. If you have already installed the Kernel 3.11 or higher and have a Radeon HD 2000 (R600) series or newer graphics card, you may wish to enable DPM feature by below steps (DRM will probably be enabled by default in Ubuntu 14.04).

1. Download the updated firmware from this directory. You need the *_smc.bin files, choose the one that matches your graphics card codename.e

The *_smc.bin files can be installed by running below command in terminal (Ctrl+Alt+T):

cd ~/Downloads/ && ./FILENAME_smc.bin

2. If you have Linux Kernel 3.11 or higher installed, now you can enable DPM by adding the radeon.dpm=1 parameter.

In terminal (Ctrl+Alt+T), run command to edit grub:

sudo gedit /etc/default/grub

Find the line that says “GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash”. Add the parameter so that it will look like:

GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash radeon.dpm=1″

3. Save the file. Update the grub:

sudo update-grub

4. You can further configure DPM by opening /etc/rc.local and adding the following line:

echo parameter > /sys/class/drm/card0/device/power_dpm_state

Where “parameter” can be:

• battery (a set of performance levels targeted for optimal operation on battery)
• balanced (a set of performance levels targeted for optimal every day use)
• performance (a set of performance levels targeted for the highest GPU performance)

via: AskUbuntu