PLDM - Platform Level Data Model

Overview

PLDM (Platform Level Data Model) is a key component of the OpenBMC project, providing a standardized data model and message formats for various platform management functionalities. It defines a method to manage, monitor, and control the firmware and hardware of a system.

The OpenBMC PLDM project aims to implement the specifications defined by the Distributed Management Task Force (DMTF), allowing for interoperable management interfaces across different hardware and firmware components.

Features

• Standardized Messaging: Adheres to the DMTF's PLDM specifications, enabling consistent and interoperable communication between different components.
• Modularity: Supports multiple PLDM types, including base, FRU,Firmware update, Platform Monitoring and Control, and BIOS Control and Configuration.
• Extensibility: Easily extendable to support new PLDM types and custom OEM commands.
• Integration: Seamlessly integrates with other OpenBMC components for comprehensive system management.

Getting Started

Prerequisites

To build and run PLDM, you need the following dependencies:

• Meson
• Ninja

Alternatively, source an OpenBMC ARM/x86 SDK.

Building

To build the PLDM project, follow these steps:

meson setup build && ninja -C build

To run unit tests

The simplest way of running the tests is as described by the meson man page:

meson setup builddir && meson setup test -C builddir

Alternatively, tests can be run in the OpenBMC CI docker container using these steps.

To enable pldm verbosity

pldm daemon accepts a command line argument --verbose or --v or -v to enable the daemon to run in verbose mode. It can be done via adding this option to the environment file that pldm service consumes.

echo 'PLDMD_ARGS="--verbose"' > /etc/default/pldmd
systemctl restart pldmd

To disable pldm verbosity

rm /etc/default/pldmd
systemctl restart pldmd

Code Organization

At a high-level, code in this repository belongs to one of the following three components.

libpldmresponder

This library provides handlers for incoming PLDM request messages. It provides for a registration as well as a plug-in mechanism. The library is implemented in modern C++, and handles OpenBMC's platform specifics.

The handlers are of the form

Response handler(Request payload, size_t payloadLen)

Source files are named according to the PLDM Type, for eg base.[hpp/cpp], fru.[hpp/cpp], etc.

OEM/vendor-specific functions

This will support OEM or vendor-specific functions and semantic information. Following directory structure has to be used:

    pldm repo
     |---- oem
            |----<oem_name>
                      |----libpldmresponder
                            |---<oem based handler files>

<oem_name> - This folder must be created with the name of the OEM/vendor in lower case. Folders named libpldm and libpldmresponder must be created under the folder <oem_name>

Files having the oem functionality for the libpldmresponder library should be placed under the folder oem/<oem_name>/libpldmresponder. They must be adhering to the rules mentioned under the libpldmresponder section above.

Once the above is done a meson option has to be created in pldm/meson_options.txt with its mapped compiler flag to enable conditional compilation.

For consistency would recommend using "oem-<oem_name>".

The pldm/meson.build and the corresponding source file(s) will need to incorporate the logic of adding its mapped compiler flag to allow conditional compilation of the code.

libpldm

pldm daemon links against the libpldm library during compilation, For more information on libpldm please refer to libpldm

pldmtool

For more information on pldmtool please refer to plmdtool/README.md.

Flows

This section documents important code flow paths.

BMC as PLDM responder

a) PLDM daemon receives PLDM request message from underlying transport (MCTP).

b) PLDM daemon routes message to message handler, based on the PLDM command.

c) Message handler decodes request payload into various field(s) of the request message. It can make use of a decode_foo_req() API, and doesn't have to perform deserialization of the request payload by itself.

d) Message handler works with the request field(s) and generates response field(s).

e) Message handler prepares a response message. It can make use of an encode_foo_resp() API, and doesn't have to perform the serialization of the response field(s) by itself.

f) The PLDM daemon sends the response message prepared at step e) to the remote PLDM device.

BMC as PLDM requester

a) A BMC PLDM requester app prepares a PLDM request message. There would be several requester apps (based on functionality/PLDM remote device). Each of them needn't bother with the serialization of request field(s), and can instead make use of an encode_foo_req() API.

b) BMC requester app requests PLDM daemon to send the request message to remote PLDM device.

c) Once the PLDM daemon receives a corresponding response message, it notifies the requester app.

d) The requester app has to work with the response field(s). It can make use of a decode_foo_resp() API to deserialize the response message.

PDR Implementation

While PLDM Platform Descriptor Records (PDRs) are mostly static information, they can vary across platforms and systems. For this reason, platform specific PDR information is encoded in platform specific JSON files. JSON files must be named based on the PDR type number. For example a state effecter PDR JSON file will be named 11.json. The JSON files may also include information to enable additional processing (apart from PDR creation) for specific PDR types, for eg mapping an effecter id to a D-Bus object.

The PLDM responder implementation finds and parses PDR JSON files to create the PDR repository. Platform specific PDR modifications would likely just result in JSON updates. New PDR type support would require JSON updates as well as PDR generation code. The PDR generator is a map of PDR Type -> C++ lambda to create PDR entries for that type based on the JSON, and to update the central PDR repo.

BIOS Support

Redfish supports the BIOS Attribute Registry, which provides users with a list of BIOS attributes supported in the BIOS configuration. To incorporate BIOS attribute registry support in openBMC, BmcWeb is designed to read data from the Base BIOS Table. PLDM populates the Base BIOS Table for the BIOS Config Manager based on BIOS JSON files. BIOS functionality is integrated into PLDM according to the guidelines in the PLDM BIOS Specification. BIOS attributes, also referred to as BIOS parameters or configuration settings, are structured within JSON files. Each attribute is defined by its name, type, and type-specific metadata. PLDM parses BIOS JSON file and creates the Base BIOS Table hosted by BIOS Config Manager. The design is documented in DesignDoc. Redfish supports BIOS Attribute registry, which provides users with the list of BIOS attributes supported in the BIOS configuration. The BIOS Attribute registry data is supposed to be derived from Base BIOS Table. PLDM populates the Base BIOS Table for BIOS Config Manager based on BIOS Json files.

After the JSON files are parsed, pldm would also create the string table, attribute table, and attribute value table as per Section7 in PLDM BIOS Specification. Those BIOS tables are exchanged with remote PLDM terminus using the GetBiosTable command as defined in DSP0247_1.0.0.pdf Section 8.1. All the bios attribute json files are kept under OEM Path. BIOS json configuration is provided in bios_attr.json file which contains attributes of type enum, integer and string.

Integer Attribute details as documented at Table9 of PLDM BIOS Specification:

{
  "entries": [
    {
      "attribute_type": "integer",
      "attribute_name": "Attribute Name",
      "lower_bound": "The lower bound on the integer value",
      "upper_bound": "The upper bound on the integer value",
      "scalar_increment": "The scalar value that is used for the increments to this integer ",
      "default_value": "The default value of the integer",
      "help_text": "Help text about attribute usage",
      "display_name": "Attribute Display Name",
      "read_only": "Read only Attribute"
    }
  ]
}

Enum Attribute details as documented at Table6 of PLDM BIOS Specification:

{
  "entries": [
    {
      "attribute_type": "enum",
      "attribute_name": "Attribute Name",
      "possible_values": [
        "An array of character strings of variable to indicate the possible values of the BIOS attribute"
      ],
      "default_values": "Default value",
      "help_text": "Help text about attribute usage",
      "display_name": "Display Name",
      "read_only": "Read only Attribute"
    }
  ]
}

String Attribute details as documented at Table7 of PLDM BIOS Specification:

{
  "entries": [
    {
      "attribute_type": "string",
      "attribute_name": "Attribute Name",
      "string_type": "It specifies the character encoding format, which can be ASCII, Hex, UTF-8, UTF-16LE, or UTF-16BE. Currently, only ASCII is supported",
      "minimum_string_length": "The minimum length of the string in bytes",
      "maximum_string_length": "The maximum length of the string in bytes",
      "default_string": "The default string itself",
      "help_text": "Help text about attribute usage",
      "display_name": "Attribute Display Name",
      "read_only": "Read only Attribute"
    }
  ]
}

As PLDM BIOS Attributes may differ across platforms and systems, supporting system-specific BIOS attributes is crucial. To achieve this, BIOS JSON files are organized under folders named after the system type. System type information is retrieved from the Entity Manager service, which hosts the Compatible Interface.

This interface dynamically populates the Names property with system type information. However, determining the system type in the application space may take some time since the compatible interface and the Names property are dynamically created by the Entity Manager. Consequently, BIOS tables are lazily constructed upon receiving the system type.

To enable system-specific BIOS attribute support within PLDM, the meson option system-specific-bios-json can be utilized. With system-specific-bios-json option enabled BIOS JSON files specific to the system type are fetched during runtime.