Hardware/GX

The Wii and GameCube's GPU is known as the GX. It was created by ArtX (who was acquired by ATI prior to the GameCube's release). It was not created by ATI, and bears 0 resemblence to any ATI Radeon GPU. It's often thought that the Flipper or Hollywood chips are the GPU, but actually, they are SoCs which contain, among many other blocks, the GX GPU.

The GX of the Wii is clocked higher (243MHz) than that of the GameCube (162MHz), with nearly no other changes.

Wii-Linux sadly does not have any drivers to interface with the GX GPU on either the GameCube or the Wii.

A bit of information as to how this GPU works is available on it's WiiBrew page, as well as in YAGCD, specifically sections 5.11 and 8.