Does the MediaTek Genio 520 support NTB-style PCIe communication between two root complexes?
The G520 does not support operation as an Endpoint (EP), meaning that the G520’s PCIe controller can only exist as a Root Port (RP). In a standard PCIe tree topology, two Root Ports cannot directly physical interface and successfully establish an NTB logical link.
The lack of support for Endpoint mode also prevents the fulfillment of the crucial “deadlock avoidance” requirement in NTB communication. The specification strictly prohibits Endpoints from having receive dependencies (i.e., it cannot require that a TLP be sent before a new TLP can be received). However, Downstream Ports (such as Root Ports) are allowed to have such dependencies.