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Fan Presence Configuration File

Table of Contents

Overview

The phosphor-fan-presence-tach application is controlled by a configuration file (config file) to manage the Present property's state on the xyz.openbmc_project.Inventory.Item interface for fan inventory objects. The config file defines the method(s) and policy(s) to use in determining the presence of each fan within a machine.

Data Format

The config file is written using the JSON (JavaScript Object Notation) data format and can be created using a text editor.

Example

See config.json.

System Config Location

The config file name is config.json.

Supported Directory

/usr/share/phosphor-fan-presence/presence/

The supported version of the config file is installed under this read-only directory location as part of the firmware image install. This is where the config file will be loaded from when no overriding config file exists.

Default Location

Where a single config file for 1-or-more system types can be used, the config file can be located at the base of the supported directory.

i.e.) /usr/share/phosphor-fan-presence/presence/config.json

Compatible System Type Location

The config file location can also be based on a system type. This is necessary where more than one type of machine is supported in a single BMC firmware image and those system types can not share a common config file.

A system type sub-directory can be obtained from the Inventory.Decorator.Compatible D-Bus interface's Names property. The property holds a list of one or more compatible system types.

Example:

  • com.ampere.Hardware.Chassis.Model.MtJade
  • com.ampere.Hardware.Chassis.Model.MtMitchell

The phosphor-fan-presence-tach application then traverses the supported directory, appending each compatible system type entry as a sub-directory on each config file until it is found.

Example:

  1. /usr/share/phosphor-fan-presence/presence/com.ampere.Hardware.Chassis.Model.MtJade/
    • (directory/config file does not exist)
  2. /usr/share/phosphor-fan-presence/presence/com.ampere.Hardware.Chassis.Model.MtMitchell/config.json
    • (config file found)

If a config file is not found and the machine is powered on, an error is logged and phosphor-fan-presence-tach application terminates preventing the machine from successfully powering on.

Override Directory

/etc/phosphor-fan-presence/presence/

A different version of the config file can be loaded by placing it into this writable directory location. This avoids the need to build and install a new firmware image on the BMC when changing the configuration, such as for testing purposes.

The override directory may not exist on the BMC, therefore to be able to use an overriding config file it must be created using the following command:

mkdir -p /etc/phosphor-fan-presence/presence

Search Order

The phosphor-fan-presence-tach application will search for the config file at the directory locations in the following order:

  1. Override directory
  2. Supported directory
    • Default location
    • Compatible System Type location

Contents

Structure

The config file consists of an array of fan objects that define how their presence is detected and the policy used to update its present state within inventory.

[
  {
    "name": "fan0",
    "path": "/system/chassis/motherboard/fan0",
    "methods": [
      {
        "type": ...
      },
      .
      .
      .
    ],
    "rpolicy": {
        "type": ...
    }
  },
  .
  .
  .
]

Syntax

Fan object attributes: (Required unless otherwise noted)

Comments

The JSON data format does not support comments. However, an optional comments attribute name can be used to annotate any specific entry of the JSON configuration. It is suggested that the value of this comments attribute be an array of strings for comments containing line breaks. All comments objects are ignored when the JSON configuration is processed.

Note: Only 1 comments object can exist at any given 'layer' of the configuration hierarchy

Example:

[
  {
    "comments": [
      "First fan in the system",
      "Uses two methods of presence detection"
    ],
    "name": "fan0",
    "path": "/system/chassis/motherboard/fan0",
    "methods": [
      {
        "comments": "Use GPIO for presence detection",
        "type": "gpio",
        .
        .
        .
      },
      {
        "comments": "Also use the tach for presence detection",
        "type": "tach",
        .
        .
        .
      }
    ],
    "rpolicy": {
        "type": ...
    }
  },
  .
  .
  .
]

Validation

TBD

Firmware Updates

When a new firmware image is installed on the BMC, it will update the config file in the standard directory.

The override directory will not be modified by a firmware update. If a config file exists in the override directory, it will continue to be used as the fan presence configuration instead of the config file located under the appropriate location within the supported directory.

Loading and Reloading

The config file is loaded when the phosphor-fan-presence-tach application starts.

To force the application to reload the config file, use the following command on the BMC:

systemctl kill -s HUP phosphor-fan-presence-tach@0.service

To confirm which config file was loaded, use the following command on the BMC:

journalctl -u phosphor-fan-presence-tach@0.service | grep Loading