@jeder yeah I've looked into it on some AMD bioses and it's kinda funny
all the support is in AGESA, so the firmware setup only has to expose the option, but of course vendors tend to do segmentation based on this and also don't advertise support properly ​:char_nachoneko_baa:​ but at least this is easily modded
there's a bit of a complication though because not all CPUs support the same bifurcation options and eg most ryzen APUs only have x8 lanes out of the CPU anyway