# phosphor-led-manager

This project manages LED groups on dbus. Sometimes many LEDs must be driven
together to indicate some system state.

For example, there can be multiple identify LEDs. When the user wants to
identify the system, they should all light up together.

## Configuration

The configuration can happen via json or yaml.

### Configuration: LED Priority

Each LED can have "Priority" as "Blink" or "On". If this property is defined, it
should be defined on each instance of the LED in the config.

When multiple LED groups are asserted and contain the same LED, "Priority"
determines the state of the LED.

For example, Group 1 says LED1 should be "Blink", and Group 2 says it should be
"On". LED1 will then have the state declared in "Priority".

### Configuration Example (JSON)

This is our configuration file. It describes 2 LEDs for the
'_enclosure_identify_' group, with their respective states and duty cycles.

```json
{
  "leds": [
    {
      "group": "enclosure_identify",
      "members": [
        {
          "Name": "pca955x_front_sys_id0",
          "Action": "On",
          "DutyOn": 50,
          "Period": 0,
          "Priority": "Blink"
        },
        {
          "Name": "led_rear_enc_id0",
          "Action": "On",
          "DutyOn": 50,
          "Period": 0,
          "Priority": "Blink"
        }
      ]
    }
  ]
}
```

Then start the program with

```text
~# ./phosphor-led-manager --config example.json
```

## Dbus interface

When starting the program, our LED group shows up on dbus. Usually there will be
many more groups.

```text
$ busctl tree xyz.openbmc_project.LED.GroupManager
`- /xyz
  `- /xyz/openbmc_project
    `- /xyz/openbmc_project/led
      `- /xyz/openbmc_project/led/groups
        `- /xyz/openbmc_project/led/groups/enclosure_identify


$ busctl introspect xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/enclosure_identify
NAME                                TYPE      SIGNATURE RESULT/VALUE FLAGS
...
xyz.openbmc_project.Led.Group       interface -         -            -
.Asserted                           property  b         false        emits-change writable
```

In the above output, the usual org.freedesktop.\* interfaces have been removed
to keep it readable.

We can now drive the entire group by setting it's 'Asserted' property on dbus.

```text
$ busctl set-property \
xyz.openbmc_project.LED.GroupManager \
/xyz/openbmc_project/led/groups/enclosure_identify \
xyz.openbmc_project.Led.Group Asserted b true
```

The program can then use the _xyz.openbmc_project.Led.Physical_ dbus interface
exposed by _phosphor-led-sysfs_ to set each LED state.

## How to Build

```text
meson setup build
cd build
ninja
```