xref: /openbmc/entity-manager/src/gpio-presence/README.md (revision b9fef4e36f512a628234f1a9b6d8241b96b38f7a) 
1# gpio-presence-sensor
2
3This program was originally implemented following the [design][].
4
5## Configuration
6
7See the full [design][] for more details.
8
9Example EM config fragments:
10
11```json
12{
13  Exposes:
14  [
15    {
16      "Name": "com.meta.Hardware.Yv4.cable0",
17      "PresencePinNames": ["presence-cable0"],
18      "PresencePinValues": [1],
19      "Type": "GPIODeviceDetect"
20    },
21    {
22      "Name": "com.meta.Hardware.Yv4.ComputeCard",
23      "PresencePinNames": ["presence-slot0a", "presence-slot0b"],
24      "PresencePinValues": [0, 1],
25      "Type": "GPIODeviceDetect"
26    },
27    {
28      "Name": "com.meta.Hardware.Yv4.SidecarExpansion",
29      "PresencePinNames": ["presence-slot0a", "presence-slot0b"],
30      "PresencePinValues": [1, 0],
31      "Type": "GPIODeviceDetect"
32    },
33    {
34      "Name": "com.meta.Hardware.Yv4.AirBlocker",
35      "PresencePinNames": ["presence-slot0a", "presence-slot0b"],
36      "PresencePinValues": [1, 1],
37      "Type": "GPIODeviceDetect"
38    },
39    {
40      "Name": "com.meta.Hardware.Yv4.fanboard0",
41      "PresencePinNames": ["presence-fanboard0"],
42      "PresencePinValues": [0],
43      "Type": "GPIODeviceDetect"
44    },
45    ...
46  ],
47  ...
48  "Name": "My Chassis",
49  "Probe": "xyz.openbmc_project.FruDevice({'BOARD_PRODUCT_NAME': 'MYBOARDPRODUCT*'})",
50  "Type": "Board",
51}
52```
53
54The above configuration can then cause a Probe match in another configuration,
55like below:
56
57```json
58{
59  Exposes:
60  [
61      {
62        "Address": "0x28",
63        "Bus": 5,
64        "EntityId": 7,
65        "EntityInstance": 0,
66        "Name": "fanboard_air_inlet",
67        "Name1": "fanboard_air_outlet",
68        "Type": "NCT7802"
69    },
70    ...
71  ],
72  ...
73  "Name": "My Fan Board 0",
74  "Probe": "xyz.openbmc_project.Inventory.Source.DevicePresence({'Name': 'com.meta.Hardware.Yv4.fanboard0'})",
75  "Type": "Board",
76}
77```
78
79Notice the **xyz.openbmc_project.Inventory.Source.DevicePresence** interface.
80This is what the gpio-presence daemon exposes on dbus when the hardware is
81detected as present. The **Name** property in the Probe statement is the same as
82configured as in the first json fragment.
83
84## Applications
85
86Applications include detecting fan boards, air blockers, cables and other simple
87components for which no standard / well-defined way exists to detect them
88otherwise.
89
90It can also be used as detection redundancy in case another detection mechanism
91like FRU eeprom is corrupted or unavailable.
92
93## References
94
95[design]:
96  https://github.com/openbmc/docs/blob/master/designs/inventory/gpio-based-hardware-inventory.md
97