Kernel driver pmbus

Supported chips:

  • Ericsson BMR453, BMR454

    Prefixes: ‘bmr453’, ‘bmr454’

    Addresses scanned: -


Author: Guenter Roeck <>


This driver supports hardware monitoring for various PMBus compliant devices. It supports voltage, current, power, and temperature sensors as supported by the device.

Each monitored channel has its own high and low limits, plus a critical limit.

Fan support will be added in a later version of this driver.

Usage Notes

This driver does not probe for PMBus devices, since there is no register which can be safely used to identify the chip (The MFG_ID register is not supported by all chips), and since there is no well defined address range for PMBus devices. You will have to instantiate the devices explicitly.

Example: the following will load the driver for an LTC2978 at address 0x60 on I2C bus #1:

$ modprobe pmbus
$ echo ltc2978 0x60 > /sys/bus/i2c/devices/i2c-1/new_device

Platform data support

Support for additional PMBus chips can be added by defining chip parameters in a new chip specific driver file. For example, (untested) code to add support for Emerson DS1200 power modules might look as follows:

static struct pmbus_driver_info ds1200_info = {
      .pages = 1,
      /* Note: All other sensors are in linear mode */
      .direct[PSC_VOLTAGE_OUT] = true,
      .direct[PSC_TEMPERATURE] = true,
      .direct[PSC_CURRENT_OUT] = true,
      .m[PSC_VOLTAGE_IN] = 1,
      .b[PSC_VOLTAGE_IN] = 0,
      .R[PSC_VOLTAGE_IN] = 3,
      .m[PSC_VOLTAGE_OUT] = 1,
      .b[PSC_VOLTAGE_OUT] = 0,
      .R[PSC_VOLTAGE_OUT] = 3,
      .m[PSC_TEMPERATURE] = 1,
      .b[PSC_TEMPERATURE] = 0,
      .R[PSC_TEMPERATURE] = 3,
                 | PMBUS_HAVE_PIN | PMBUS_HAVE_POUT
                 | PMBUS_HAVE_FAN12 | PMBUS_HAVE_STATUS_FAN12,

static int ds1200_probe(struct i2c_client *client,
                        const struct i2c_device_id *id)
      return pmbus_do_probe(client, id, &ds1200_info);

static int ds1200_remove(struct i2c_client *client)
      return pmbus_do_remove(client);

static const struct i2c_device_id ds1200_id[] = {
      {"ds1200", 0},

MODULE_DEVICE_TABLE(i2c, ds1200_id);

/* This is the driver that will be inserted */
static struct i2c_driver ds1200_driver = {
      .driver = {
                 .name = "ds1200",
      .probe = ds1200_probe,
      .remove = ds1200_remove,
      .id_table = ds1200_id,

static int __init ds1200_init(void)
      return i2c_add_driver(&ds1200_driver);

static void __exit ds1200_exit(void)

Sysfs entries

When probing the chip, the driver identifies which PMBus registers are supported, and determines available sensors from this information. Attribute files only exist if respective sensors are supported by the chip. Labels are provided to inform the user about the sensor associated with a given sysfs entry.

The following attributes are supported. Limits are read-write; all other attributes are read-only.

inX_input Measured voltage. From READ_VIN or READ_VOUT register.
inX_min Minimum Voltage. From VIN_UV_WARN_LIMIT or VOUT_UV_WARN_LIMIT register.
inX_max Maximum voltage. From VIN_OV_WARN_LIMIT or VOUT_OV_WARN_LIMIT register.
inX_lcrit Critical minimum Voltage. From VIN_UV_FAULT_LIMIT or VOUT_UV_FAULT_LIMIT register.
inX_crit Critical maximum voltage. From VIN_OV_FAULT_LIMIT or VOUT_OV_FAULT_LIMIT register.
inX_min_alarm Voltage low alarm. From VOLTAGE_UV_WARNING status.
inX_max_alarm Voltage high alarm. From VOLTAGE_OV_WARNING status.
inX_lcrit_alarm Voltage critical low alarm. From VOLTAGE_UV_FAULT status.
inX_crit_alarm Voltage critical high alarm. From VOLTAGE_OV_FAULT status.
inX_label “vin”, “vcap”, or “voutY”
currX_input Measured current. From READ_IIN or READ_IOUT register.
currX_max Maximum current. From IIN_OC_WARN_LIMIT or IOUT_OC_WARN_LIMIT register.
currX_lcrit Critical minimum output current. From IOUT_UC_FAULT_LIMIT register.
currX_crit Critical maximum current. From IIN_OC_FAULT_LIMIT or IOUT_OC_FAULT_LIMIT register.
currX_alarm Current high alarm. From IIN_OC_WARNING or IOUT_OC_WARNING status.
currX_max_alarm Current high alarm. From IIN_OC_WARN_LIMIT or IOUT_OC_WARN_LIMIT status.
currX_lcrit_alarm Output current critical low alarm. From IOUT_UC_FAULT status.
currX_crit_alarm Current critical high alarm. From IIN_OC_FAULT or IOUT_OC_FAULT status.
currX_label “iin”, “iinY”, “iinY.Z”, “ioutY”, or “ioutY.Z”, where Y reflects the page number and Z reflects the phase.
powerX_input Measured power. From READ_PIN or READ_POUT register.
powerX_cap Output power cap. From POUT_MAX register.
powerX_max Power limit. From PIN_OP_WARN_LIMIT or POUT_OP_WARN_LIMIT register.
powerX_crit Critical output power limit. From POUT_OP_FAULT_LIMIT register.
powerX_alarm Power high alarm. From PIN_OP_WARNING or POUT_OP_WARNING status.
powerX_crit_alarm Output power critical high alarm. From POUT_OP_FAULT status.
powerX_label “pin”, “pinY”, “pinY.Z”, “poutY”, or “poutY.Z”, where Y reflects the page number and Z reflects the phase.
tempX_input Measured temperature. From READ_TEMPERATURE_X register.
tempX_min Mimimum temperature. From UT_WARN_LIMIT register.
tempX_max Maximum temperature. From OT_WARN_LIMIT register.
tempX_lcrit Critical low temperature. From UT_FAULT_LIMIT register.
tempX_crit Critical high temperature. From OT_FAULT_LIMIT register.
tempX_min_alarm Chip temperature low alarm. Set by comparing READ_TEMPERATURE_X with UT_WARN_LIMIT if TEMP_UT_WARNING status is set.
tempX_max_alarm Chip temperature high alarm. Set by comparing READ_TEMPERATURE_X with OT_WARN_LIMIT if TEMP_OT_WARNING status is set.
tempX_lcrit_alarm Chip temperature critical low alarm. Set by comparing READ_TEMPERATURE_X with UT_FAULT_LIMIT if TEMP_UT_FAULT status is set.
tempX_crit_alarm Chip temperature critical high alarm. Set by comparing READ_TEMPERATURE_X with OT_FAULT_LIMIT if TEMP_OT_FAULT status is set.