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LED Support for OpenBMC

This document describes how to add LED support for your machine based upon the OpenBMC LED Architecture document. LED group management is done automatically for machines that support the use of the MRW and is beyond the scope of this document.

D-Bus

Service     xyx.openbmc_project.LED.GroupManager
Path        /xyz/openbmc_project/led/groups/<label>
Interfaces  xyz.openbmc_project.Led.Group

Signals: none
Attribute: Asserted (boolean)

REST

PUT /xyz/openbmc_project/led/groups/<group>/attr/Asserted

The LED group state can be changed by setting the Asserted value to boolean 0 or 1. In the following example, the lamp_test group is being asserted...

 curl -b cjar -k -X PUT -H "Content-Type: application/json" -d '{"data":  1}' \
  https://${bmc}/xyz/openbmc_project/led/groups/lamp_test/attr/Asserted

REDFISH

Resource identify Operation

Starting with Redfish v2020.3, Redfish resources have LocationIndicatorActive property, which is used to identify a particular resource. This is for LED Identify operation only.

All applicable Inventory D-Bus objects would have a forward association mapping to LED Group D-Bus object, namely:

 - identify_led_group

All applicable LED Group D-Bus objects would have an association mapping to inventory D-Bus object, namely:

 - identify_inventory_object

When a LocationIndicatorActive GET operation is performed on the resource, bmcweb does below operations:

  • Look for an association identify_led_group on the Inventory D-Bus object
  • If found, read the asserted property from the D-Bus object that is pointed to by identify_led_group

When a LocationIndicatorActive PATCH operation is performed on the resource, bmcweb does below operations:

  • Look for an association identify_led_group on the Inventory D-Bus object
  • If found, set the asserted property on the D-Bus object that is pointed to by identify_led_group

Representing resource faults

For representing the fault status of a resource, Redfish Health property is used. All applicable Inventory D-Bus objects would have a forward association mapping to LED Group D-Bus object, namely;

 - fault_led_group

All applicable LED Group D-Bus objects would have an association mapping to inventory D-Bus object, namely:

 - fault_inventory_object

When a component fault is detected, the responsible code sets the Functional property of xyz.openbmc_project.State.Decorator.OperationalStatus to false on the Inventory D-Bus object.

When LED manager gets PropertyChanged signal, it does the following:

  • Look for an association fault_led_group on the Inventory D-Bus object

  • Turn on/off the fault LED group depending on the value of Functional false would mean turn ON the LED group true would mean turn OFF the LED group

  • bmcweb already has a design to look for Functional property and set the Health property.

Development Details

There are two significant layers for LED operations. The physical and the logical. The LED Group Manager communicates with the physical LED Manager to drive the physical LEDs. The logical groups are defined in the machine's led.yaml file. LED Group manager consumes this and creates D-Bus/REST interfaces for the individual LEDs that are part of the group.

Defining the physical LED

Physical LED wiring is defined in the leds section of the machine's device tree. See the Palmetto DTS as an example.

Add a fault LED to the device tree with a corresponding gpio pin...

  leds {
    compatible = "gpio-leds";

    fault {
      gpios = <&gpio ASPEED_GPIO(N, 2) GPIO_ACTIVE_LOW>;
    };
  }

The kernel will then create...

 ls -l /sys/class/leds/fault/
total 0
-rw-r--r--    1 root     root          4096 Jun 21 20:04 brightness
lrwxrwxrwx    1 root     root             0 Jun 21 20:29 device -> ../../../leds
-r--r--r--    1 root     root          4096 Jun 21 20:29 max_brightness
drwxr-xr-x    2 root     root             0 Jun 21 20:29 power
lrwxrwxrwx    1 root     root             0 Jun 21 20:04 subsystem -> ../../../../../class/leds
-rw-r--r--    1 root     root          4096 Jun 21 20:04 trigger
-rw-r--r--    1 root     root          4096 Jun 21 20:04 uevent

Defining Groups

An LED Group can contain zero or more LEDs and is defined in the machines led.yaml. The default one will likely need to be tailored to your machines layout. Customized yaml files are placed into the machines specific Yocto location. As an example:

meta-ibm/meta-palmetto/recipes-phosphor/leds/palmetto-led-manager-config/led.yaml

The parent properties in the yaml file will be created below /xyz/openbmc_project/led/groups/. The children properties need to map to an LED name in /sys/class/leds.

In the example, below two URIs would be created: /xyz/openbmc_project/led/groups/enclosure_fault and /xyz/openbmc_project/led/groups/lamp_test. Both act on the same physical LED fault but do so differently. The lamp_test would also drive a blink signal to the physical power LED if one was created.

EnclosureFault:
    fault:
        Action: 'On'
        DutyOn: 50
        Period: 0
lamp_test:
    fault:
        Action: 'Blink'
        DutyOn: 20
        Period: 100
    power:
        Action: 'Blink'
        DutyOn: 20
        Period: 100

Required Groups

OpenBMC Architecture requires specific LED Groups to be created and are documented in the D-Bus interface.

Yocto packaging

  1. Create a tailored LED manager file

    E.g. meta-ibm/meta-romulus/recipes-phosphor/leds/romulus-led-manager-config-native.bb

    SUMMARY = "Phosphor LED Group Management for Romulus"
PR = "r1"

inherit native
inherit obmc-phosphor-utils
inherit obmc-phosphor-license

PROVIDES += "virtual/phosphor-led-manager-config-native"

SRC_URI += "file://led.yaml"
S = "${WORKDIR}"

# Overwrites the default led.yaml
do_install() {
    SRC=${S}
    DEST=${D}${datadir}/phosphor-led-manager
    install -D ${SRC}/led.yaml ${DEST}/led.yaml
}

  2. Change your machine's preferred provider for the led-manager in the conf file

    E.g. meta-ibm/meta-romulus/conf/machine/romulus.conf

    PREFERRED_PROVIDER_virtual/phosphor-led-manager-config-native = "romulus-led-manager-config-native"