Valve might need some not yet upstreamed kernel features for Steam Deck, but what is the ustpream kernel missing otherwise for gaming? I use it without any issu

Valve might need some not yet upstreamed kernel features for Steam Deck, but what is the ustpream kernel missing otherwise for gaming? I use it without any issues. As far as I know they also prefer to upstream things in general. I think AMD's amd-pstate / amd-pstate-epp and related work was kicked off becasue of Steam Deck, but it all went upstream.