The Experimental GCN 1.0 GPU Support Might Be Dropped From AMDGPU Linux Driver

By default the Linux kernel selects the aging Radeon DRM driver for GCN 1.0 "Southern Islands" and GCN 1.1 "Sea Islands" hardware (as well as all older ATI/AMD GPUs) while it's GCN 1.2 and newer that defaults to the modern AMDGPU kernel driver. But for years there has been experimental GCN 1.0/1.1 support available via kernel module options, but now for the original GCN GPUs that code is at risk of being dropped.

The GCN 1.0/1.1 support within AMDGPU has remained experimental and hidden by default even though it's generally worked well, sometimes offers better performance, and is necessary if wanting Vulkan support via RADV or AMDVLK. Enabling the support has required booting the kernel with radeon.si_support=0 radeon.cik_support=0 amdgpu.si_support=1 amdgpu.cik_support=1.

While the AMDGPU driver often works well for these early GCN graphics processors, features like UVD video decoding have not been wired up. There's also other occasional bugs for lack of testing / no official support from AMD in using this support but rather just the Radeon DRM default.

A Phoronix reader pointed out this mailing list discussion from earlier in December. The post revealed that AMD is unlikely to release updated GPU firmware to enable UVD to work with the AMDGPU driver architecture.

But more interesting is word that AMD is looking at "considering dropping SI support completely from AMDGPU." This would leave the default Radeon DRM driver with GCN 1.0 support while GCN 1.1 users could still opt for this newer driver option. Presumably the dropping of GCN 1.0 from AMDGPU is due to bugs and acknowledging that at least via their resources the AMDGPU driver will not be reaching parity to the older Radeon DRM code.