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/\<label\>/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

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

A LED Group can contain zero or more LEDs and 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-openbmc-machines/meta-openpower/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 dbus interface

Yocto packaging

1. Create a tailored LED manager file

meta-openbmc-machines/meta-openpower/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 peferred provider for the led-manager in the conf file

i.e. meta-openbmc-machines/meta-openpower/meta-ibm/meta-romulus/conf/machine/romulus.conf

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

Additional Reading

D-Bus Interfaces Managing LED groups