I've been having this problem lately:
My Fedora 20 would freeze; after a while, while using the <em>xorg-x11-drv-ati</em> driver.
Another thing I noticed, was the fan of the card going up and up like crazy.
First thing I did, was install <em>lm_sensors</em>:
yum -y install lm_sensors
And ran the <em>sensors</em> command:
# sensors
radeon-pci-0100
Adapter: PCI adapter
temp1: +85.5°C (crit = +120.0°C, hyst = +90.0°C)
k10temp-pci-00c3
Adapter: PCI adapter
temp1: +38.6°C (high = +70.0°C)
(crit = +90.0°C, hyst = +85.0°C)
Wow! 75.5 ºC on my AMD/Ati card! I know why the freezes happen now! It overheats and crashes!
So, I'll do what you need to do when you have problems: RTFM!
http://xorg.freedesktop.org/wiki/RadeonFeature/#index3h2
Now, there is a hint right there. You can try and control the power profile; but that is not exactly it. You want the system to do it for you.
To immediately lower the temperature on my video card, I recurred to the following commands:
echo profile > /sys/class/drm/card0/device/power_method
echo low > /sys/class/drm/card0/device/power_profile
My answer was enabling dpm; by adding <em>radeon.dpm=1</em> to the kernel line at <em>/etc/grub2-efi.conf</em> (in my case).
So, it looks something like this:
linuxefi /vmlinuz-3.12.9-301.fc20.x86_64 root=UUID=6c9b3ffd-c911-4dcb-9425-e44841ab379d ro rootflags=subvol=root vconsole.font=latarcyrheb-sun16 rhgb quiet LANG=en_US.UTF-8 radeon.dpm=1
initrdefi /initramfs-3.12.9-301.fc20.x86_64.img
Update 2014-07-11: It seems that the <em>radeon.dpm</em> solution is preventing 3d acceleration on my vanilla Fedora 20 installation; preventing gdm (all but LightDm) from working. I have to confirm this later by changing this statement.
Ok, now, the next thing is to rebuild my initrd image with dracut; which proved to be really easy:
su -
dracut --force
Basically, if you don't do that, you will be dropped to a shell when booting; just exit that and you're good.