A system needs two groups of configurations: zones and sensors.
They can come either from a dedicated config file or via D-Bus from e.g. entity-manager.
If config file does not exist the configuration is obtained from a set of D-Bus interfaces. When using entity-manager to provide them refer to Pid, Pid.Zone and Stepwise schemas. The key names are not identical to JSON but similar enough to see the correspondence.
Default config file path /usr/share/swampd/config.json can be overridden by using --conf command line option.
The JSON object should be a dictionary with two keys, sensors and zones. sensors is a list of the sensor dictionaries, whereas zones is a list of zones.
"sensors" : [
{
"name": "fan1",
"type": "fan",
"readPath": "/xyz/openbmc_project/sensors/fan_tach/fan1",
"writePath": "/sys/devices/platform/ahb/ahb:apb/1e786000.pwm-tacho-controller/hwmon/**/pwm1",
"min": 0,
"max": 255,
"ignoreDbusMinMax": true
"unavailableAsFailed": true
},
{
"name": "fan2",
"type": "fan",
"readPath": "/xyz/openbmc_project/sensors/fan_tach/fan2",
"writePath": "/sys/devices/platform/ahb/ahb:apb/1e786000.pwm-tacho-controller/hwmon/**/pwm2",
"min": 0,
"max": 255,
"timeout": 4,
},
...
A sensor has a name, a type, a readPath, a writePath, a minimum value, a maximum value, a timeout, a ignoreDbusMinMax and a unavailableAsFailed value.
The name is used to reference the sensor in the zone portion of the configuration.
The type is the type of sensor it is. This influences how its value is treated. Supported values are: fan, temp, and margin.
The readPath is the path that tells the daemon how to read the value from this sensor. It is optional, allowing for write-only sensors. If the value is absent or None it'll be treated as a write-only sensor.
If the readPath value contains: /xyz/openbmc_project/extsensors/ it'll be treated as a sensor hosted by the daemon itself whose value is provided externally. The daemon will own the sensor and publish it to dbus. This is currently only supported for temp and margin sensor types.
If the readPath value contains: /xyz/openbmc_project/ (this is checked after external), then it's treated as a passive dbus sensor. A passive dbus sensor is one that listens for property updates to receive its value instead of actively reading the Value property.
If the readPath value contains: /sys/ this is treated as a directly read sysfs path. There are two supported paths:
/sys/class/hwmon/hwmon0/pwm1/sys/devices/platform/ahb/1e786000.pwm-tacho-controller/hwmon/<asterisk asterisk>/pwm1The writePath is the path to set the value for the sensor. This is only valid for a sensor of type fan. The path is optional. If can be empty or None. It then only supports two options.
If the writePath value contains: /sys/ this is treated as a directory written sysfs path. There are two support paths:
/sys/class/hwmon/hwmon0/pwm1/sys/devices/platform/ahb/1e786000.pwm-tacho-controller/hwmon/<asterisk asterisk>/pwm1If the writePath value contains: /xyz/openbmc_project/sensors/fan_tach/fan{N} it sets of a sensor object that writes over dbus to the xyz.openbmc_project.Control.FanPwm interface. The writePath should be the full object path.
busctl introspect xyz.openbmc_project.Hwmon-1644477290.Hwmon1 /xyz/openbmc_project/sensors/fan_tach/fan1 --no-pager
NAME TYPE SIGNATURE RESULT/VALUE FLAGS
org.freedesktop.DBus.Introspectable interface - - -
.Introspect method - s -
org.freedesktop.DBus.Peer interface - - -
.GetMachineId method - s -
.Ping method - - -
org.freedesktop.DBus.Properties interface - - -
.Get method ss v -
.GetAll method s a{sv} -
.Set method ssv - -
.PropertiesChanged signal sa{sv}as - -
xyz.openbmc_project.Control.FanPwm interface - - -
.Target property t 255 emits-change writable
xyz.openbmc_project.Sensor.Value interface - - -
.MaxValue property x 0 emits-change writable
.MinValue property x 0 emits-change writable
.Scale property x 0 emits-change writable
.Unit property s "xyz.openbmc_project.Sensor.Value.Uni... emits-change writable
.Value property x 2823 emits-change writable
The minimum and maximum values are optional. When maximum is non-zero it expects to write a percentage value converted to a value between the minimum and maximum.
The timeout value is optional and controls the sensor failure behavior. If a sensor is a fan the default value is 2 seconds, otherwise it's 0. When a sensor's timeout is 0 it isn't checked against a read timeout failure case. If a sensor fails to be read within the timeout period, the zone goes into failsafe to handle the case where it doesn't know what to do -- as it doesn't have all its inputs.
The ignoreDbusMinMax value is optional and defaults to false. The dbus passive sensors check for a MinValue and MaxValue and scale the incoming values via these. Setting this property to true will ignore MinValue and MaxValue from dbus and therefore won't call any passive value scaling.
The unavailableAsFailed value is optional and defaults to true. However, some specific thermal sensors should not be treated as Failed when they are unavailable. For example, when a system is powered-off, its CPU/DIMM Temp sensors are unavailable, in such state these sensors should not be treated as Failed and trigger FailSafe. This is important for systems whose Fans are always on. For these specific sensors set this property to false.
"zones" : [
{
"id": 1,
"minThermalOutput": 3000.0,
"failsafePercent": 75.0,
"pids": [],
...
Each zone has its own fields, and a list of controllers.
| field | type | meaning |
|---|---|---|
id | int64_t | This is a unique identifier for the zone. |
minThermalOutput | double | This is the minimum value that should be considered from the thermal outputs. Commonly used as the minimum fan RPM. |
failsafePercent | double | If there is a fan PID, it will use this value if the zone goes into fail-safe as the output value written to the fan's sensors. |
pids | list of strings | Fan and thermal controllers used by the zone. |
The id field here is used in the d-bus path to talk to the xyz.openbmc_project.Control.Mode interface.
TODO: Examine how the fan controller always treating its output as a percentage works for future cases.
A zone collects all the setpoints and ceilings from the thermal controllers attached to it, selects the maximum setpoint, clamps it by the minimum ceiling and minThermalOutput; the result is used to control fans.
There are fan, temp, margin (PID), and stepwise (discrete steps) controllers.
The fan PID is meant to drive fans or other cooling devices. It's expecting to get the setpoint value from the owning zone and then drive the fans to that value.
A temp PID is meant to drive the setpoint given an absolute temperature value (higher value indicates warmer temperature).
A margin PID is meant to drive the setpoint given a margin value (lower value indicates warmer temperature, in other words, it's the safety margin remaining expressed in degrees Celsius).
The setpoint output from the thermal controllers is called RPMSetpoint() However, it doesn't need to be an RPM value.
TODO: Rename this method and others to not say necessarily RPM.
Some PID configurations have fields in common, but may be interpreted differently.
When using D-Bus, each configuration can have a list of strings called Profiles. In this case the controller will be loaded only if at least one of them is returned as Current from an object implementing xyz.openbmc_project.Control.ThermalMode interface (which can be anywhere on D-Bus). swampd will automatically reload full configuration whenever Current is changed.
D-Bus Name attribute is used for indexing in certain cases so should be unique for all defined configurations.
If the PID type is not stepwise then the PID field is defined as follows:
| field | type | meaning |
|---|---|---|
samplePeriod | double | How frequently the value is sampled. 0.1 for fans, 1.0 for temperatures. |
proportionalCoeff | double | The proportional coefficient. |
integralCoeff | double | The integral coefficient. |
feedFwdOffsetCoeff | double | The feed forward offset coefficient. |
feedFwdGainCoeff | double | The feed forward gain coefficient. |
integralLimit_min | double | The integral minimum clamp value. |
integralLimit_max | double | The integral maximum clamp value. |
outLim_min | double | The output minimum clamp value. |
outLim_max | double | The output maximum clamp value. |
slewNeg | double | Negative slew value to dampen output. |
slewPos | double | Positive slew value to accelerate output. |
The units for the coefficients depend on the configuration of the PIDs.
If the PID is a margin controller and its setpoint is in centigrade and output in RPM: proportionalCoeff is your p value in units: RPM/C and integral coefficient: RPM/C sec
If the PID is a fan controller whose output is pwm: proportionalCoeff is %/RPM and integralCoeff is %/RPM sec.
NOTE: The sample periods are specified in the configuration as they are used in the PID computations, however, they are not truly configurable as they are used for the update periods for the fan and thermal sensors.
"name": "fan1-5",
"type": "fan",
"inputs": ["fan1", "fan5"],
"setpoint": 90.0,
"pid": {
...
}
The type fan builds a FanController PID.
| field | type | meaning |
|---|---|---|
name | string | The name of the PID. This is just for humans and logging. |
type | string | fan |
inputs | list of strings | The names of the sensor(s) that are used as input and output for the PID loop. |
setpoint | double | Presently UNUSED |
pid | dictionary | A PID dictionary detailed above. |
"name": "fleetingpid0",
"type": "margin",
"inputs": ["fleeting0"],
"setpoint": 10,
"pid": {
...
}
The type margin builds a ThermalController PID.
| field | type | meaning |
|---|---|---|
name | string | The name of the PID. This is just for humans and logging. |
type | string | margin |
inputs | list of strings | The names of the sensor(s) that are used as input for the PID loop. |
setpoint | double | The setpoint value for the thermal PID. The setpoint for the margin sensors. |
pid | dictionary | A PID dictionary detailed above. |
Each input is normally a temperature difference between some hardware threshold and the current state. E.g. a CPU sensor can be reporting that it's 20 degrees below the point when it starts thermal throttling. So the lower the margin temperature, the higher the corresponding absolute value.
Out of all the inputs the minimal value is selected and used as an input for the PID loop.
The output of a margin PID loop is that it sets the setpoint value for the zone. It does this by adding the value to a list of values. The value chosen by the fan PIDs (in this cascade configuration) is the maximum value.
Exactly the same as margin but all the inputs are supposed to be absolute temperatures and so the maximal value is used to feed the PID loop.
"name": "temp1",
"type": "stepwise",
"inputs": ["temp1"],
"setpoint": 30.0,
"pid": {
"samplePeriod": 0.1,
"positiveHysteresis": 1.0,
"negativeHysteresis": 1.0,
"isCeiling": false,
"reading": {
"0": 45,
"1": 46,
"2": 47,
},
"output": {
"0": 5000,
"1": 2400,
"2": 2600,
}
}
The type stepwise builds a StepwiseController.
| field | type | meaning |
|---|---|---|
name | string | The name of the controller. This is just for humans and logging. |
type | string | stepwise |
inputs | list of strings | The names of the sensor(s) that are used as input and output for the controller. |
pid | dictionary | A controller settings dictionary detailed below. |
The pid dictionary (confusingly named) is defined as follows:
| field | type | meaning |
|---|---|---|
samplePeriod | double | Presently UNUSED. |
reading | dictionary | Enumerated list of input values, indexed from 0, must be monotonically increasing, maximum 20 items. |
output | dictionary | Enumerated list of output values, indexed from 0, must match the amount of reading items. |
positiveHysteresis | double | How much the input value must raise to allow the switch to the next step. |
negativeHysteresis | double | How much the input value must drop to allow the switch to the previous step. |
isCeiling | bool | Whether this controller provides a setpoint or a ceiling for the zone |
setpoint | double | Presently UNUSED. |
NOTE: reading and output are normal arrays and not embedded in the dictionary in Entity Manager.
Each measurement cycle out of all the inputs the maximum value is selected. Then it's compared to the list of reading values finding the largest that's still lower or equal the input (the very first item is used even if it's larger than the input). The corresponding output value is selected if hysteresis allows the switch (the current input value is compared with the input present at the moment of the previous switch). The result is added to the list of setpoints or ceilings for the zone depending on isCeiling setting.