Radeon Video

The following instructions are for modern AMD GPU chipsets covered by the radeon and amdgpu drivers.

Firmware

For Vega and later, the linux-firmware-amdgpu package is required. Otherwise, the linux-firmware-radeon should be used.

See the relevant section on the Gentoo Wiki for a more granular list of product names and microarchitecture names.

To enable KMS at boot:

Add the radeon or amdgpu and fbcon modules to /etc/modules:
$ echo radeon >> /etc/modules
$ echo fbcon >> /etc/modules
or
$ echo amdgpu >> /etc/modules
$ echo fbcon >> /etc/modules
Install mkinitfs:
apk add mkinitfs
Enable the kms feature in the mkinitfs configuration by adding it to the features variable, e.g.,
Contents of /etc/mkinitfs/mkinitfs.conf
features="keymap cryptsetup kms ata base ide scsi usb virtio ext4"
Run mkinitfs.
Reboot to test the configuration.

Install the following packages as needed:

mesa-dri-gallium: necessary Mesa drivers.
mesa-va-gallium: VA-API drivers, for hardware accelerated video encoding and decoding

If driver auto-selection does not work, e.g. no mouse cursor under Sway, manual driver selection might be needed:

export MESA_LOADER_DRIVER_OVERRIDE=r300: for AMD's Radeon R300, R400, and R500 GPUs.
export MESA_LOADER_DRIVER_OVERRIDE=r600: for AMD's Radeon R600 GPUs up to Northern Islands. Officially supported by AMD.
export MESA_LOADER_DRIVER_OVERRIDE=radeonsi: for AMD's Southern Island GPUs and later. Officially supported by AMD.

For VA-API:

Install either the Free Software driver xf86-video-ati or the proprietary amdgpu firmware linux-firmware-amdgpu.

modprobe fbcon might be needed to avoid black screen when leaving Xorg.