X.org includes a driver, radeon, for recent ATI graphic chips (i.e., those branded "Radeon"). This driver supports 2D acceleration and some other chip features. In conjunction with a suitable DRI driver such as r300, it also provides 3D acceleration.
Kernel Mode setting (KMS)
KMS is new and is introduced for the ATI Radeon graphics chips in kernel 2.6.31, and is still marked as part of Staging because there is a potential local security issue with using it.
It basically means that the kernel is responsible for the initialization and setup of the video card. And removes a long standing contention between the kernel and userspace.
KMS on radeon is the default on Fedora 11 and newer
KMS on radeon has some known limitations for now, including
- Lack of Svideo output support (partly fixed in 2.6.32)
- No graphics card Power Management, see agd5f in Phoronix Forums
- Possibly multi display support being broken. Particulair on older chips (RV250 and older) you might encounter various display corruption problems, or have no acceleration (RV100). If you encounter problems, you can disable KMS by booting with the
User Mode setting (UMS)
UMS is the legacy mode setting, and is used when the kernel does not support modesetting, or if it is disabled. It basically means the radeon xorg driver does the initialization and modesetting itself.
Supported graphic chips
- ATI Mobility Radeon 7000
- ATI Mobility Radeon 7500
- ATI Mobility Radeon 9000
- ATI Mobility Radeon 9600
- ATI Mobility Radeon X300
- ATI Mobility Radeon X600