Translations:Xorg/Guide/31/en
From Gentoo Wiki
The first variable is VIDEO_CARDS. This is used to set the video drivers that intended to be used, and is usually based on the kind of video card present. The most common settings are nouveau for NVIDIA cards or radeon for AMD cards. Both have actively developed, well-supported open-source drivers. For newer AMD video cards (Southern Islands and up), there is also the open-source amdgpu driver. See the AMDGPU article for more details.