Changing DPM power state with Fedora 19

[Hamish Wilson]

I recently installed an RV630 GPU into my HTPC so that its screen could use its DVI input and because the on-board Nvidia was giving me some instability problems with Nouveau. As this computer is not being used for gaming or anything else all that intensive I hoped that I could force the card to run at its lowest and most efficient power state, but for some reason Fedora 19 is not letting me do anything at with it:

[root@localhost ~]# echo low > /sys/class/drm/card0/device/power_dpm_force_performance_level
-bash: /sys/class/drm/card0/device/power_dpm_force_performance_level: Permission denied
[root@localhost ~]# echo battery > /sys/class/drm/card0/device/power_dpm_state
-bash: /sys/class/drm/card0/device/power_dpm_state: Permission denied
[root@localhost ~]# chmod a+w /sys/class/drm/card0/device/power_dpm_force_performance_level
chmod: cannot access ?/sys/class/drm/card0/device/power_dpm_force_performance_level?: No such file or directory
[root@localhost ~]# chmod a+w /sys/class/drm/card0/device/power_dpm_state
chmod: cannot access ?/sys/class/drm/card0/device/power_dpm_state?: No such file or directory
[root@localhost ~]#

The system is using the Linux 3.14 kernel, but I have set the radeon.dpm=1 parameter regardless.