When I first superficially looked at the Nvidia TX2 card i noticed two things: a) HDMI port, and b) video encoding SDK. First though: oh cool, I can encode inbound HDMI signals. On second inspection, nope. That is an outbound HDMI port.
Hmm.. how does one get video into the unit? Well, it does have the CSI2 ports. Then the next search is: anything having to do with HDMI to CSI2 signal conversion?
One of the search results is a Raspberry Pi forum discussion of a HDMI to CSI adapter board using a TC358743 camera bridge. The 746 version.
As a side bar to that forum discussion, one salient point is that many of the initial Pi devices have only two of four possible 1 gbps lanes: "not going to work easily with a A, B, B+, or B2, particularly as they all only expose 2-lane CSI-2". Another form article about HDMI to CSI-2 via TC358743 on kernel 4.1 using more recent Pi versions and a auvidea B101 HDMI to CSI-2 bridge.
The Nvidia Jetson TX1/TX2 handle four lanes.
The Toshiba TC358840 is a follow on part to the TC358743 and able to handle 4K Ultra HD.