This repo aims to implement MCTP and PLDM protocols from the PMCI specifications. This provides platform management functionality in the BMCs managing the server platforms.

Management Component Transport Protocol (MCTP) provides a common transport layer protocol for the application layer protocols providing platform manageability solutions. The physical layer protocols like I2C, PCIe etc are abstracted out of management protocols. MCTP specification also defines how management controllers can be connected in a network and defines commands for formation and maintainence of MCTP network.

PLDM defines data structures and commands that abstract platform management subsystem components. PLDM supports a Type field to distinguish various types of messages and group them together based on the functions(Ex: FRU, Monitoring & Control, Firmware Update etc.)

MCTP Base Specification

MCTP SMBus Binding Specification

MCTP PCIe Binding Specification

PLDM over MCTP binding Specification

PLDM Base Specification

PLDM IDs and Codes specification

PLDM Monitoring and Control Specification

PLDM State Set Specification

PLDM FRU Specification

PLDM Firmware Update Specification

Note: Each of these components are organised in a separate directory, and a README is added for each of these for more information.

Entity Manager advertises MCTP configurations specific to the platform. This is used by pmci-launcher service, which starts multiple instances of MCTP Service. The same service can be used to start upper layer protocols (PLDM/SPDM etc.) based on the platform configurations.

The MCTP service instance can either start in Endpoint mode or in Bus Owner mode. When the MCTP service instance comes up in endpoint mode, BMC comes up with the special EID 0; the bus owner in that physical medium needs to assign EID to BMC. When the MCTP service instance comes up in Bus Owner mode, BMC discovers MCTP capable devices on the physical medium and assign EIDs from a pre-configured EID pool (provided by Entity Manager).

MCTP Service will expose interfaces to enable upper layer protocols to discover, send and receive the MCTP messages.

Note: In current architecture, MCTP Bridging is not supported. Each physical bus forms a separate MCTP network.

Upper layer protocols can use mctpwplus library to interact with the MCTP layer. The mctpwplus library provides the following:

1. Abstraction from IPC mechansim of the MCTP transport layer.

2. APIs to discover newly added/removed device in MCTP network.

3. APIs to send and receive MCTP payloads.

The current mctpwplus library works in conjuction with the IntelBMC mctp implementation (i.e. using D-Bus), however the design goal is to incorporate other implementations too (i.e. socket based MCTP transport).

A sample upper layer protocol like PLDM is represented in the figure above. PLDM is transport layer agnostic and will be able to send out PLDM packets over various MCTP bindings like SMBus, PCIe etc.

This particular repo depends on the following:

1. libmctp : This library provides the MCTP core functionality (MCTP message assembly/dissassembly, binding specific TX and RX methods).This can be picked up from Intel fork of libmctp: Intel-BMC libmctp

This library supports the SMBus and PCIe bindings out of the box (for Aspeed 26xx controllers). If you need custom bindings to be supported, please feel free to add code for custom bindings.

2. kernel drivers : The libmctp in turn works with Kernel drivers. For the SMBus binding, a custom driver called slave-mqueue and patches for handling I2C muxes are required. The PCIe binding requires the driver that controlls mctp-pcie controller (in AST26xx SoCs). The reference implementation is available in: Intel-BMC linux

3. OpenBMC dependencies : This repo aligns with concepts used in OpenBMC project (D-Bus based IPC mechanisms, usage of boost library for async operations, etc.). These dependencies are required for the code to build.

To integrate the features into your BMC, the following recipes can be used as a reference in your Yocto build: PMCI recipes