Defaulting Radeon GCN 1.0/1.1 GPUs To Better Linux Driver Is Held Up By Analog Outputs

Switching from the "Radeon" to "AMDGPU" kernel driver on Linux is possible for Radeon GCN 1.0/1.1 era graphics cards and doing so can mean slight performance benefits, the ability to run the AMDVLK or RADV Vulkan drivers, and simply making use of this better maintained driver. But having these original GCN graphics cards default to the modern AMDGPU driver appears held up by the lack of analog video output support with that driver.

In recent months there was work on GCN 1.0 UVD video decode for AMDGPU as what was one of the main blockers and reasons why some Radeon users want to use that driver in place of AMDGPU. But that's been fixed in the latest Linux kernel builds and work on DC display support as well as GPU reset support, among other minor lingering features for AMDGPU that were unsupported for these older Graphics Core Next GPUs.

So while AMDGPU is in very good shape for GCN 1.0/1.1, one of the main features that appears to be blocking the driver from using it by default is for lacking analog video output support within AMDGPU's "DC" display core. The Radeon DRM driver meanwhile supports those remaining graphics cards with analog outputs fine.

The lack of analog output support was brought up in this mailing list thread started by RADV co-founder Bas Nieuwenhuizen.

He was inquiring about making AMDGPU the default for these Southern Islands and Sea Islands GPUs, but in response was the lack of analog connector support within DC and also HDMI/DP audio support when running without DC enabled. The HDMI/DP audio support could be cleared up more easily than the lack of analog support. DC (formerly DAL) is designed for modern AMD graphics cards needs and really past the point of analog video outputs, thus leading to an awkward situation now. It doesn't appear there is anyone at AMD or external community/third-party developers working on said support.

While it may not be the default, those on these older graphics cards wanting to use the AMDGPU driver can boot with the kernel options of radeon.si_support=0 radeon.cik_support=0 amdgpu.si_support=1 amdgpu.cik_support=1. Hopefully some Linux distribution vendors will decide to make that call themselves as well especially given analog connectors on GCN 1.0/1.1 hardware being not too common and then users actually relying upon said connectors with these graphics cards being even more rare.