One of the missing features if you are using a GCN 1.0 "Southern Islands" graphics card and want to use the AMDGPU DRM driver rather than Radeon DRM is that UVD video decoding is currently unsupported. But there's new patches to fix that.

Independent developer Piotr Redlewski has posted a set of seven kernel patches for wiring in UVD Southern Islands support for the AMDGPU DRM driver. These patches are based upon the UVD support in Radeon DRM and then the GCN 1.1 UVD support already within AMDGPU DRM.

This video decoding support for the original AMD GCN graphics cards in AMDGPU DRM also requires some firmware changes and there are a few other issues to tackle before it could be merged, but hopefully we'll see that happen soon so GCN 1.0 is closer to parity for using this newer Direct Rendering Manager driver.

Patches and details on amd-gfx.