MCTP D-Bus interfaces are implemented by the MCTP control process daemon alias mcptd and aids in the discovery of MCTP enabled devices by application layer protocols (like PLDM, SPDM) which are implemented in the userspace. Application layer protocols will rely on the discovery of xyz.openbmc_project.MCTP.Endpoint D-Bus interface to discover MCTP endpoints. The supported MCTP message types in an endpoint are exposed by the SupportedMessageTypes property in the xyz.openbmc_project.MCTP.Endpoint interface. For example, if the endpoint supports PLDM then pldm daemon will complete the PLDM discovery flow with the MCTP endpoint. Also mctpd discovers the removal of the MCTP endpoints and removes the D-Bus objects corresponding to those endpoints. MCTP bridges are not modelled in the D-Bus.
The root D-Bus object path for the mctpd is /xyz/openbmc_project/mctp. There will be a D-Bus object for every endpoint that is discovered by the mctpd. The lifetime of the D-Bus object is the lifetime of the connected MCTP device.
The D-Bus object path for MCTP endpoints are named xyz/openbmc_project/mctp/<NetworkId>/<EID> where NetworkId is the locally defined network identfier the endpoint is part of and EID is the endpoint ID. This aids in the enumeration of the endpoints belonging to an MCTP network. The D-Bus object implements the xyz.openbmc_project.MCTP.Endpoint interface. The object may also optionally implement xyz.openbmc_project.Common.UUID interface to address the requirement for devices with multiple endpoints and for hot-plug devices.
An MCTP Network may provide an optional MCTP Network ID that can be used to differentiate different MCTP Networks when more than one MCTP Network can be accessed by an entity . The Network ID is also used when an entity has more than one point of access to the MCTP Network. The MCTP Network ID enables the entity to tell whether the access points provide access to the same MCTP Network or to different MCTP Networks. If the implementation supports the optional MCTP network ID then it is exposed on the D-Bus. The D-Bus object path is xyz/openbmc_project/mctp/<NetworkId> where NetworkId is the locally defined network identfier and implements the xyz.openbmc_project.Common.UUID interface and the UUID property is the MCTP network ID.