The linux-tegra mailing list is the canonical communication channel when it comes to upstream Linux kernel development.
I should add here that both Alex and I focus almost exclusively on upstream development, which may or may not be what you're looking for. On one hand, upstream is where most of the new technologies are developed, so it's the "bleeding edge" from that point of view. On the other hand the amount of manpower that goes into upstream development is limited, so the upstream kernel might lack a bunch of features that you might be interested in. That said, we are working very hard on getting upstream closer to L4T/Android from a feature perspective and would very much welcome contributors.
We also have an IRC channel (#tegra on Freenode) that we use for realtime communication. If you're interested in chatting with us, feel free to drop by.
I should add here that both Alex and I focus almost exclusively on upstream development, which may or may not be what you're looking for. On one hand, upstream is where most of the new technologies are developed, so it's the "bleeding edge" from that point of view. On the other hand the amount of manpower that goes into upstream development is limited, so the upstream kernel might lack a bunch of features that you might be interested in. That said, we are working very hard on getting upstream closer to L4T/Android from a feature perspective and would very much welcome contributors.
We also have an IRC channel (#tegra on Freenode) that we use for realtime communication. If you're interested in chatting with us, feel free to drop by.