Hardware/GX

The Wii and GameCube's GPU is known as the GX. The Wii U's Latte SoC also has GX for compatibility with Wii software, active only in vWii mode, disabled in native mode. 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 does not yet have fully-featured graphics acceleration using GX, however recent mainline kernels do use GX for framebuffer color conversion; RGB (which Linux expects) to YUYV (which VI expects). There is also experimental work to have full 3D rendering on GX through a DRM driver, though it is not yet in any release.

NetBSD also lacks full graphics acceleration using GX, but it also uses it for framebuffer color conversion, albeit in a more CPU-hungry way (using the CPU to copy data into the EFB, then using GX to do the final convert/copy into the XFB) than Linux does (rendering the framebuffer as a texture, through an indirect texture, into the EFB, then using GX to do the final convert/copy into the XFB)

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.