Skip to main content

PlatformManager Presence Detection

PlatformManager supports detecting whether a PmUnit (FRU) is physically present in a slot. This enables hot-plug detection and proper handling of optional components.

Overview​

Presence detection determines if a PmUnit is plugged into a slot before attempting to explore it. This prevents errors when accessing empty slots and enables reporting of which slots are populated.

Detection Methods​

GPIO Line Handle​

Uses a GPIO line from a gpio chip to detect presence:

{
  "presenceDetection": {
    "gpioLineHandle": {
      "devicePath": "/[SCM_CPLD_GPIO]",
      "lineIndex": 5,
      "desiredValue": 1
    }
  }
}
  • devicePath: DevicePath to the gpio chip device
  • lineIndex: GPIO line number (0-indexed)
  • desiredValue: Value indicating presence (typically 0 or 1)

Sysfs File Handle​

Uses a sysfs file to detect presence:

{
  "presenceDetection": {
    "sysfsFileHandle": {
      "devicePath": "/[SMB_CPLD]",
      "presenceFileName": "pim1_present",
      "desiredValue": 1
    }
  }
}
  • devicePath: DevicePath to the device exposing the sysfs file
  • presenceFileName: Name of the sysfs file containing presence status
  • desiredValue: Value indicating presence

Configuration​

Presence detection is configured per-slot in SlotConfig:

{
  "outgoingSlotConfigs": {
    "PIM_SLOT@0": {
      "slotType": "PIM_SLOT",
      "presenceDetection": {
        "gpioLineHandle": {
          "devicePath": "/[IOB_GPIO]",
          "lineIndex": 0,
          "desiredValue": 1
        }
      },
      "outgoingI2cBusNames": ["IOB_I2C_0@0"]
    }
  }
}

Presence Info Response​

When querying PmUnit info via the Thrift API, presence information is included:

PmUnitInfo {
  name: "PIM8DD",
  presenceInfo: {
    presenceDetection: { ... },
    actualValue: 1,
    isPresent: true
  },
  successfullyExplored: true
}
  • actualValue: The raw value read from the GPIO or sysfs file
  • isPresent: Whether the actual value matches the desired value

Exploration Behavior​

  1. If presenceDetection field is configured for a slot:

    • PlatformManager checks presence before exploring
    • If FRU is absent: the slot is skipped and a SLOT_PM_UNIT_ABSENCE error is recorded
    • If FRU is present: normal exploration proceeds

  2. If presenceDetection field is NOT configured:

    • The slot is assumed to always be populated
    • Exploration proceeds directly

Expected Empty Slots​

Some slots may be expected to be empty. These are tracked separately from unexpected failures. When a slot is expected to be empty, its absence is reported as SUCCEEDED_WITH_EXPECTED_ERRORS rather than FAILED. Currently, only PSU_SLOT types are treated as expected-to-be-empty.

Hardware Requirements​

For GPIO-based presence detection:

  • The GPIO chip must be created before checking presence
  • Parent PmUnit must be explored first

For sysfs-based presence detection:

  • The device exposing the sysfs file must be created first
  • The sysfs file must be readable