AMD Posts Code Enabling "Cyan Skillfish" Display Support Due To Different DCN2 Variant

Since July we've seen AMD open-source driver engineers posting code for "Cyan Skillfish" as an APU with Navi 1x graphics. While initial support for Cyan Skillfish was merged for Linux 5.15, it turns out the display code isn't yet wired up due to being a different DCN2 variant for its display block.

Cyan Skillfish is in a bit of an odd position since its a Navi 1x RDNA APU where as other leaks/rumors showed AMD moving straight from the existing Vega-based APUs over to Navi 2x / RDNA2 and not matching with other road-map expectations... Especially with the AMDGPU Linux driver stack already busy preparing for Yellow Carp / Rembrandt and Van Gogh. Possibly pointing to Cyan Skillfish being more of a custom APU design is that it has slightly different display IP compared to existing RDNA/RDNA2 hardware.

The patches posted for enabling Cyan Skillfish display support add Display Core Next 2.01 "DCN201" display engine support. This DCN 2.01 support comes while existing AMD graphics processors already have Display Core Next 2.1, 3.0. 3,01, and 3.02 variants.

AMD Renoir APUs with Vega graphics utilizing DCN 2.1 IP so it's a bit awkward that Cyan Skillfish with Navi 1x would seemingly step back a bit to DCN "2.01" at least as far as conventional versioning is concerned. It's with RDNA2 where there is the DCN3 display engine.

In any case, these patches adding some 34k lines of new code due to the new DCN2 variant gets display output working for Cyan Skillfish. As usual, much of the high line count is due to automated header files.

Given the timing and assuming no major defects in this Cyan Skillfish display code, it should be merged later this year for Linux 5.16.