AMD GPU support requires the linux-firmware-amd package. If you have installed
the linux or linux-lts packages, it will be installed as a dependency. If
you installed a version-specific kernel package (e.g., linux5.4), it may be
necessary to manually install linux-firmware-amd.
Install the Mesa DRI package, mesa-dri. This is already included in the xorg
meta-package, but it is needed when installing Xorg via xorg-minimal or for
running a Wayland compositor.
Install vulkan-loader, the Khronos Vulkan Loader. Then install one or both of
the Mesa AMD Vulkan driver, mesa-vulkan-radeon; or the GPUOpen AMD Vulkan
driver, amdvlk.
Installing the xorg meta-package will pull in both xf86-video-amdgpu and,
for older hardware, xf86-video-ati. If you install xorg-minimal, choose one
of these Xorg driver packages to match your hardware. The amdgpu driver should
support cards built on AMD's "Graphics Core Next 1.2" architecture, introduced
circa 2012.
For VA-API, install the mesa-vaapi package. To ensure the AMD VA-API driver is
used, set the environment variable LIBVA_DRIVER_NAME to radeonsi.
For VDPAU, install libvdpau-va-gl. Set the environment variable VDPAU_DRIVER
to va_gl.