[PATCH 3/3] pmbus: Add driver for Maxim MAX31785 Intelligent Fan Controller

[Andrew Jeffery]

The Maxim MAX31785 is a PMBus device providing closed-loop,
multi-channel fan management with temperature and remote voltage
sensing. Various fan control features are provided, including PWM
frequency control, temperature hysteresis, dual tachometer measurements,
and fan health monitoring.

The driver implementation makes use of the new fan control virtual
registers exposed by the pmbus core. It mixes use of the default
implementations with some overrides via the read/write handlers to
handle FAN_COMMAND_1 on the MAX31785, whose definition breaks the value
range into various control bands dependent on RPM or PWM mode.

The dual tachometer feature is implemented in hardware with a TACHSEL
line to indicate the rotor under measurement, and exposed on the bus by
extending the READ_FAN_SPEED_1 word with two extra bytes*.
The need to read the non-standard four-byte response leads to a cut-down
implementation of i2c_smbus_xfer_emulated() included in the driver.
Further, to expose the second rotor tachometer value to userspace,
virtual fans are implemented by re-routing the FAN_CONFIG_1_2 register
from the undefined (in hardware) pages 23-28 to the same register on
pages 0-5, and similarly re-routing READ_FAN_SPEED_1 requests on 23-28
to pages 0-5 but extracting the second word of the four-byte response.

* The documentation recommends the slower rotor be associated with
TACHSEL=0, which provides the first word of the response. The TACHSEL=0
measurement is used by the controller's closed-loop fan management.

Signed-off-by: Andrew Jeffery <andrew@xxxxxxxx>
---
 drivers/hwmon/pmbus/Kconfig    |  10 +
 drivers/hwmon/pmbus/Makefile   |   1 +
 drivers/hwmon/pmbus/max31785.c | 670 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 681 insertions(+)
 create mode 100644 drivers/hwmon/pmbus/max31785.c

diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
index cad1229b7e17..5f2f3c6c7499 100644
--- a/drivers/hwmon/pmbus/Kconfig
+++ b/drivers/hwmon/pmbus/Kconfig
@@ -95,6 +95,16 @@ config SENSORS_MAX20751
 	  This driver can also be built as a module. If so, the module will
 	  be called max20751.
 
+config SENSORS_MAX31785
+	tristate "Maxim MAX31785 and compatibles"
+	default n
+	help
+	  If you say yes here you get hardware monitoring support for Maxim
+	  MAX31785.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called max31785.
+
 config SENSORS_MAX34440
 	tristate "Maxim MAX34440 and compatibles"
 	default n
diff --git a/drivers/hwmon/pmbus/Makefile b/drivers/hwmon/pmbus/Makefile
index 562132054aaf..4ea548a8af46 100644
--- a/drivers/hwmon/pmbus/Makefile
+++ b/drivers/hwmon/pmbus/Makefile
@@ -10,6 +10,7 @@ obj-$(CONFIG_SENSORS_LTC2978)	+= ltc2978.o
 obj-$(CONFIG_SENSORS_LTC3815)	+= ltc3815.o
 obj-$(CONFIG_SENSORS_MAX16064)	+= max16064.o
 obj-$(CONFIG_SENSORS_MAX20751)	+= max20751.o
+obj-$(CONFIG_SENSORS_MAX31785)	+= max31785.o
 obj-$(CONFIG_SENSORS_MAX34440)	+= max34440.o
 obj-$(CONFIG_SENSORS_MAX8688)	+= max8688.o
 obj-$(CONFIG_SENSORS_TPS40422)	+= tps40422.o
diff --git a/drivers/hwmon/pmbus/max31785.c b/drivers/hwmon/pmbus/max31785.c
new file mode 100644
index 000000000000..1c2648ce5322
--- /dev/null
+++ b/drivers/hwmon/pmbus/max31785.c
@@ -0,0 +1,670 @@
+/*
+ * Copyright (C) 2017 IBM Corp.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include "pmbus.h"
+
+enum max31785_regs {
+	MFR_REVISION		= 0x9b,
+	MFR_FAULT_RESPONSE	= 0xd9,
+	MFR_TEMP_SENSOR_CONFIG	= 0xf0,
+	MFR_FAN_CONFIG		= 0xf1,
+	MFR_READ_FAN_PWM	= 0xf3,
+	MFR_FAN_FAULT_LIMIT	= 0xf5,
+	MFR_FAN_WARN_LIMIT	= 0xf6,
+	MFR_FAN_PWM_AVG		= 0xf8,
+};
+
+#define MAX31785			0x3030
+#define MAX31785A			0x3040
+
+#define MFR_TEMP_SENSOR_CONFIG_ENABLE	BIT(15)
+#define MFR_TEMP_SENSOR_CONFIG_OFFSET	GENMASK(14, 10)
+
+#define MFR_FAN_CONFIG_FREQ		GENMASK(15, 13)
+#define MFR_FAN_CONFIG_DUAL_TACH	BIT(12)
+#define MFR_FAN_CONFIG_HYS		GENMASK(11, 10)
+#define MFR_FAN_CONFIG_TSFO		BIT(9)
+#define MFR_FAN_CONFIG_TACHO		BIT(8)
+#define MFR_FAN_CONFIG_RAMP		GENMASK(7, 5)
+#define MFR_FAN_CONFIG_HEALTH		BIT(4)
+#define MFR_FAN_CONFIG_ROTOR_HI_LO	BIT(3)
+#define MFR_FAN_CONFIG_ROTOR		BIT(2)
+#define MFR_FAN_CONFIG_SPIN		GENMASK(1, 0)
+
+#define MFR_FAULT_RESPONSE_MONITOR	BIT(0)
+
+#define MAX31785_CAP_READ_DUAL_TACH	BIT(0)
+
+#define MAX31785_NR_PAGES		23
+
+static int max31785_read_byte_data(struct i2c_client *client, int page,
+				   int reg)
+{
+	switch (reg) {
+	case PMBUS_VOUT_MODE:
+		if (page < MAX31785_NR_PAGES)
+			return -ENODATA;
+
+		return -ENOTSUPP;
+	case PMBUS_FAN_CONFIG_12:
+		if (page < MAX31785_NR_PAGES)
+			return -ENODATA;
+
+		return pmbus_read_byte_data(client, page - MAX31785_NR_PAGES,
+					    reg);
+	}
+
+	return -ENODATA;
+}
+
+static int max31785_write_byte(struct i2c_client *client, int page, u8 value)
+{
+	if (page < MAX31785_NR_PAGES)
+		return -ENODATA;
+
+	return -ENOTSUPP;
+}
+
+static int max31785_read_long_data(struct i2c_client *client, int page,
+				   int reg, u32 *data)
+{
+	unsigned char cmdbuf[1];
+	unsigned char rspbuf[4];
+	int rc;
+
+	struct i2c_msg msg[2] = {
+		{
+			.addr = client->addr,
+			.flags = 0,
+			.len = sizeof(cmdbuf),
+			.buf = cmdbuf,
+		},
+		{
+			.addr = client->addr,
+			.flags = I2C_M_RD,
+			.len = sizeof(rspbuf),
+			.buf = rspbuf,
+		},
+	};
+
+	cmdbuf[0] = reg;
+
+	rc = pmbus_set_page(client, page);
+	if (rc < 0)
+		return rc;
+
+	rc = i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg));
+	if (rc < 0)
+		return rc;
+
+	*data = (rspbuf[0] << (0 * 8)) | (rspbuf[1] << (1 * 8)) |
+		(rspbuf[2] << (2 * 8)) | (rspbuf[3] << (3 * 8));
+
+	return rc;
+}
+
+static int max31785_get_pwm(struct i2c_client *client, int page)
+{
+	int config;
+	int command;
+
+	config = pmbus_read_byte_data(client, page, PMBUS_FAN_CONFIG_12);
+	if (config < 0)
+		return config;
+
+	command = pmbus_read_word_data(client, page, PMBUS_FAN_COMMAND_1);
+	if (command < 0)
+		return command;
+
+	if (!(config & PB_FAN_1_RPM)) {
+		if (command >= 0x8000)
+			return 0;
+		else if (command >= 0x2711)
+			return 0x2710;
+
+		return command;
+	}
+
+	return 0;
+}
+
+static int max31785_get_pwm_mode(struct i2c_client *client, int page)
+{
+	int config;
+	int command;
+
+	config = pmbus_read_byte_data(client, page, PMBUS_FAN_CONFIG_12);
+	if (config < 0)
+		return config;
+
+	command = pmbus_read_word_data(client, page, PMBUS_FAN_COMMAND_1);
+	if (command < 0)
+		return command;
+
+	if (!(config & PB_FAN_1_RPM)) {
+		if (command >= 0x8000)
+			return 2;
+		else if (command >= 0x2711)
+			return 0;
+
+		return 1;
+	}
+
+	return (command >= 0x8000) ? 2 : 1;
+}
+
+static int max31785_read_word_data(struct i2c_client *client, int page,
+				   int reg)
+{
+	int rv;
+
+	switch (reg) {
+	case PMBUS_READ_FAN_SPEED_1:
+	{
+		u32 val;
+
+		if (page < MAX31785_NR_PAGES)
+			return -ENODATA;
+
+		rv = max31785_read_long_data(client, page - MAX31785_NR_PAGES,
+					     reg, &val);
+		if (rv < 0)
+			return rv;
+
+		rv = (val >> 16) & 0xffff;
+		break;
+	}
+	case PMBUS_VIRT_PWM_1:
+		if (page >= MAX31785_NR_PAGES)
+			return -ENOTSUPP;
+
+		rv = max31785_get_pwm(client, page);
+		if (rv < 0)
+			return rv;
+
+		rv *= 255;
+		rv /= 100;
+		break;
+	case PMBUS_VIRT_PWM_ENABLE_1:
+		if (page >= MAX31785_NR_PAGES)
+			return -ENOTSUPP;
+
+		rv = max31785_get_pwm_mode(client, page);
+		break;
+	default:
+		rv = (page >= MAX31785_NR_PAGES) ? -ENXIO : -ENODATA;
+		break;
+	}
+
+	return rv;
+}
+
+static const int max31785_pwm_modes[] = { 0x7fff, 0x2710, 0xffff };
+
+static int max31785_write_word_data(struct i2c_client *client, int page,
+				    int reg, u16 word)
+{
+	if (page >= MAX31785_NR_PAGES)
+		return -ENXIO;
+
+	switch (reg) {
+	case PMBUS_VIRT_PWM_ENABLE_1:
+		if (word >= ARRAY_SIZE(max31785_pwm_modes))
+			return -EINVAL;
+
+		return pmbus_update_fan(client, page, 0, 0, PB_FAN_1_RPM,
+					max31785_pwm_modes[word]);
+	default:
+		break;
+	}
+
+	return -ENODATA;
+}
+
+/*
+ * Returns negative error codes if an unrecoverable problem is detected, 0 if a
+ * recoverable problem is detected, or a positive value on success.
+ */
+static int max31785_of_fan_config(struct i2c_client *client,
+				  struct pmbus_driver_info *info,
+				  u32 capabilities, struct device_node *child)
+{
+	int mfr_cfg = 0, mfr_fault_resp = 0, pb_cfg;
+	struct device *dev = &client->dev;
+	char *lock_polarity = NULL;
+	const char *sval;
+	u32 page;
+	u32 uval;
+	int ret;
+
+	if (!of_device_is_compatible(child, "pmbus-fan"))
+		return 0;
+
+	ret = of_property_read_u32(child, "reg", &page);
+	if (ret < 0) {
+		dev_err(&client->dev, "Missing valid reg property\n");
+		return ret;
+	}
+
+	if (!(info->func[page] & PMBUS_HAVE_FAN12)) {
+		dev_err(dev, "Page %d does not have fan capabilities\n", page);
+		return -ENXIO;
+	}
+
+	ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, page);
+	if (ret < 0)
+		return ret;
+
+	pb_cfg = i2c_smbus_read_byte_data(client, PMBUS_FAN_CONFIG_12);
+	if (pb_cfg < 0)
+		return pb_cfg;
+
+	if (!(pb_cfg & PB_FAN_1_INSTALLED)) {
+		dev_warn(dev, "Fan %d is configured but not installed\n", page);
+		return 0;
+	}
+
+	ret = of_property_read_string(child, "maxim,fan-rotor-input", &sval);
+	if (ret < 0) {
+		dev_err(dev, "Missing valid maxim,fan-rotor-input property for fan %d\n",
+				page);
+		return ret;
+	}
+
+	if (strcmp("tach", sval) && strcmp("lock", sval)) {
+		dev_err(dev, "maxim,fan-rotor-input has invalid value for fan %d: %s\n",
+				page, sval);
+		return -EINVAL;
+	} else if (!strcmp("lock", sval)) {
+		mfr_cfg |= MFR_FAN_CONFIG_ROTOR;
+
+		ret = i2c_smbus_write_word_data(client, MFR_FAN_FAULT_LIMIT, 1);
+		if (ret < 0)
+			return ret;
+
+		ret = of_property_read_string(child, "maxim,fan-lock-polarity",
+					      &sval);
+		if (ret < 0) {
+			dev_err(dev, "Missing valid maxim,fan-lock-polarity property for fan %d\n",
+					page);
+			return ret;
+		}
+
+		if (strcmp("low", sval) && strcmp("high", sval)) {
+			dev_err(dev, "maxim,fan-lock-polarity has invalid value for fan %d: %s\n",
+					page, lock_polarity);
+			return -EINVAL;
+		} else if (!strcmp("high", sval))
+			mfr_cfg |= MFR_FAN_CONFIG_ROTOR_HI_LO;
+	}
+
+	if (!of_property_read_string(child, "fan-mode", &sval)) {
+		if (!strcmp("rpm", sval))
+			pb_cfg |= PB_FAN_1_RPM;
+		else if (!strcmp("pwm", sval))
+			pb_cfg &= ~PB_FAN_1_RPM;
+		else {
+			dev_err(dev, "fan-mode has invalid value for fan %d: %s\n",
+					page, sval);
+			return -EINVAL;
+		}
+	}
+
+	ret = of_property_read_u32(child, "tach-pulses", &uval);
+	if (ret < 0) {
+		pb_cfg &= ~PB_FAN_1_PULSE_MASK;
+	} else if (uval && (uval - 1) < 4) {
+		pb_cfg = ((pb_cfg & ~PB_FAN_1_PULSE_MASK) | ((uval - 1) << 4));
+	} else {
+		dev_err(dev, "tach-pulses has invalid value for fan %d: %u\n",
+				page, uval);
+		return -EINVAL;
+	}
+
+	if (of_property_read_bool(child, "maxim,fan-health"))
+		mfr_cfg |= MFR_FAN_CONFIG_HEALTH;
+
+	if (of_property_read_bool(child, "maxim,fan-no-watchdog") ||
+		of_property_read_bool(child, "maxim,tmp-no-fault-ramp"))
+		mfr_cfg |= MFR_FAN_CONFIG_TSFO;
+
+	if (of_property_read_bool(child, "maxim,fan-dual-tach")) {
+		mfr_cfg |= MFR_FAN_CONFIG_DUAL_TACH;
+
+		if (capabilities & MAX31785_CAP_READ_DUAL_TACH) {
+			int virtual = MAX31785_NR_PAGES + page;
+
+			info->pages = max(info->pages, virtual + 1);
+			info->func[virtual] |= PMBUS_HAVE_FAN12;
+		}
+	}
+
+	if (of_property_read_bool(child, "maxim,fan-no-fault-ramp"))
+		mfr_cfg |= MFR_FAN_CONFIG_TACHO;
+
+	if (!of_property_read_u32(child, "maxim,fan-startup", &uval)) {
+		uval /= 2;
+		if (uval < 5) {
+			mfr_cfg |= uval;
+		} else {
+			dev_err(dev, "maxim,fan-startup has invalid value for fan %d: %u\n",
+					page, uval);
+			return -EINVAL;
+		}
+	}
+
+	if (!of_property_read_u32(child, "maxim,fan-ramp", &uval)) {
+		if (uval < 8) {
+			mfr_cfg |= uval << 5;
+		} else {
+			dev_err(dev, "maxim,fan-ramp has invalid value for fan %d: %u\n",
+					page, uval);
+			return -EINVAL;
+		}
+	}
+
+	if (!of_property_read_u32(child, "maxim,tmp-hysteresis", &uval)) {
+		uval /= 2;
+		uval -= 1;
+		if (uval < 4) {
+			mfr_cfg |= uval << 10;
+		} else {
+			dev_err(dev, "maxim,tmp-hysteresis has invalid value for fan %d, %u\n",
+					page, uval);
+			return -EINVAL;
+		}
+	}
+
+	if (!of_property_read_u32(child, "maxim,fan-pwm-freq", &uval)) {
+		u16 val;
+
+		if (uval == 30) {
+			val = 0;
+		} else if (uval == 50) {
+			val = 1;
+		} else if (uval == 100) {
+			val = 2;
+		} else if (uval == 150) {
+			val = 3;
+		} else if (uval == 25000) {
+			val = 7;
+		} else {
+			dev_err(dev, "maxim,fan-pwm-freq has invalid value for fan %d: %u\n",
+					page, uval);
+			return -EINVAL;
+		}
+
+		mfr_cfg |= val << 13;
+	}
+
+	if (of_property_read_bool(child, "maxim,fan-fault-pin-mon"))
+		mfr_fault_resp |= MFR_FAULT_RESPONSE_MONITOR;
+
+	ret = i2c_smbus_write_byte_data(client, PMBUS_FAN_CONFIG_12,
+					pb_cfg & ~PB_FAN_1_INSTALLED);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_write_word_data(client, MFR_FAN_CONFIG, mfr_cfg);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_write_byte_data(client, MFR_FAULT_RESPONSE,
+					mfr_fault_resp);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_write_byte_data(client, PMBUS_FAN_CONFIG_12, pb_cfg);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Fans are on pages 0 - 5. If the page property of a fan node is
+	 * greater than 5 we will have errored in checks above out above.
+	 * Therefore we don't need to cope with values up to 31, and the int
+	 * return type is enough.
+	 *
+	 * The bit mask return value is used to populate a bitfield of fans
+	 * who are both configured in the devicetree _and_ reported as
+	 * installed by the hardware. Any fans that are not configured in the
+	 * devicetree but are reported as installed by the hardware will have
+	 * their hardware configuration updated to unset the installed bit.
+	 */
+	return BIT(page);
+}
+
+static int max31785_of_tmp_config(struct i2c_client *client,
+				  struct pmbus_driver_info *info,
+				  struct device_node *child)
+{
+	struct device *dev = &client->dev;
+	u16 mfr_tmp_cfg = 0;
+	int nr_fans;
+	u32 page;
+	u32 uval;
+	int ret;
+	int i;
+
+	if (!of_device_is_compatible(child, "pmbus-temperature"))
+		return 0;
+
+	ret = of_property_read_u32(child, "reg", &page);
+	if (ret < 0) {
+		dev_err(&client->dev, "Missing valid reg property\n");
+		return ret;
+	}
+
+	if (!(info->func[page] & PMBUS_HAVE_TEMP)) {
+		dev_err(dev, "Page %d does not have temp capabilities\n", page);
+		return -ENXIO;
+	}
+
+	ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, page);
+	if (ret < 0)
+		return ret;
+
+	if (!of_property_read_u32(child, "maxim,tmp-offset", &uval)) {
+		if (uval < 32)
+			mfr_tmp_cfg |= uval << 10;
+	}
+
+	nr_fans = of_property_count_elems_of_size(child, "maxim,tmp-fans",
+						  sizeof(u32));
+	if (nr_fans > 0) {
+		mfr_tmp_cfg |= MFR_TEMP_SENSOR_CONFIG_ENABLE;
+
+		for (i = 0; i < nr_fans; i++) {
+			if (of_property_read_u32_index(child, "maxim,tmp-fans",
+						       i, &uval))
+				continue;
+
+			if (uval < 6)
+				mfr_tmp_cfg |= BIT(uval);
+		}
+	}
+
+	ret = i2c_smbus_write_word_data(client, MFR_TEMP_SENSOR_CONFIG,
+					mfr_tmp_cfg);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+#define MAX31785_FAN_FUNCS \
+	(PMBUS_HAVE_FAN12 | PMBUS_HAVE_STATUS_FAN12 | PMBUS_HAVE_PWM12)
+
+#define MAX31785_TEMP_FUNCS \
+	(PMBUS_HAVE_TEMP | PMBUS_HAVE_STATUS_TEMP)
+
+#define MAX31785_VOUT_FUNCS \
+	(PMBUS_HAVE_VOUT | PMBUS_HAVE_STATUS_VOUT)
+
+static const struct pmbus_driver_info max31785_info = {
+	.pages = MAX31785_NR_PAGES,
+
+	.write_word_data = max31785_write_word_data,
+	.read_byte_data = max31785_read_byte_data,
+	.read_word_data = max31785_read_word_data,
+	.write_byte = max31785_write_byte,
+
+	/* RPM */
+	.format[PSC_FAN] = direct,
+	.m[PSC_FAN] = 1,
+	.b[PSC_FAN] = 0,
+	.R[PSC_FAN] = 0,
+	/* PWM */
+	.format[PSC_PWM] = direct,
+	.m[PSC_PWM] = 1,
+	.b[PSC_PWM] = 0,
+	.R[PSC_PWM] = 2,
+	.func[0] = MAX31785_FAN_FUNCS,
+	.func[1] = MAX31785_FAN_FUNCS,
+	.func[2] = MAX31785_FAN_FUNCS,
+	.func[3] = MAX31785_FAN_FUNCS,
+	.func[4] = MAX31785_FAN_FUNCS,
+	.func[5] = MAX31785_FAN_FUNCS,
+
+	.format[PSC_TEMPERATURE] = direct,
+	.m[PSC_TEMPERATURE] = 1,
+	.b[PSC_TEMPERATURE] = 0,
+	.R[PSC_TEMPERATURE] = 2,
+	.func[6]  = MAX31785_TEMP_FUNCS,
+	.func[7]  = MAX31785_TEMP_FUNCS,
+	.func[8]  = MAX31785_TEMP_FUNCS,
+	.func[9]  = MAX31785_TEMP_FUNCS,
+	.func[10] = MAX31785_TEMP_FUNCS,
+	.func[11] = MAX31785_TEMP_FUNCS,
+	.func[12] = MAX31785_TEMP_FUNCS,
+	.func[13] = MAX31785_TEMP_FUNCS,
+	.func[14] = MAX31785_TEMP_FUNCS,
+	.func[15] = MAX31785_TEMP_FUNCS,
+	.func[16] = MAX31785_TEMP_FUNCS,
+
+	.format[PSC_VOLTAGE_OUT] = direct,
+	.m[PSC_VOLTAGE_OUT] = 1,
+	.b[PSC_VOLTAGE_OUT] = 0,
+	.R[PSC_VOLTAGE_OUT] = 0,
+	.func[17] = MAX31785_VOUT_FUNCS,
+	.func[18] = MAX31785_VOUT_FUNCS,
+	.func[19] = MAX31785_VOUT_FUNCS,
+	.func[20] = MAX31785_VOUT_FUNCS,
+	.func[21] = MAX31785_VOUT_FUNCS,
+	.func[22] = MAX31785_VOUT_FUNCS,
+};
+
+static int max31785_probe(struct i2c_client *client,
+			  const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct device_node *child;
+	struct pmbus_driver_info *info;
+	u32 fans;
+	u32 caps;
+	s64 ret;
+	int i;
+
+	info = devm_kzalloc(dev, sizeof(struct pmbus_driver_info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	*info = max31785_info;
+
+	ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, 255);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_read_word_data(client, MFR_REVISION);
+	if (ret < 0)
+		return ret;
+
+	caps = 0;
+	if (!strcmp("max31785a", id->name)) {
+		if (ret == MAX31785A)
+			caps |= MAX31785_CAP_READ_DUAL_TACH;
+		else
+			dev_warn(dev, "Expected max3175a, found max31785: cannot provide secondary tachometer readings\n");
+	} else if (!strcmp("max31785", id->name)) {
+		if (ret == MAX31785A)
+			dev_info(dev, "Expected max31785, found max3175a: suppressing secondary tachometer attributes\n");
+	} else {
+		return -EINVAL;
+	}
+
+
+	fans = 0;
+	for_each_child_of_node(dev->of_node, child) {
+		ret = max31785_of_fan_config(client, info, caps, child);
+		if (ret < 0) {
+			of_node_put(child);
+			return ret;
+		}
+
+		if (ret)
+			fans |= ret;
+
+		ret = max31785_of_tmp_config(client, info, child);
+		if (ret < 0) {
+			of_node_put(child);
+			return ret;
+		}
+	}
+
+	for (i = 0; i < MAX31785_NR_PAGES; i++) {
+		bool have_fan = !!(info->func[i] & PMBUS_HAVE_FAN12);
+		bool fan_configured = !!(fans & BIT(i));
+
+		if (!have_fan || fan_configured)
+			continue;
+
+		ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, i);
+		if (ret < 0)
+			return ret;
+
+		ret = i2c_smbus_read_byte_data(client, PMBUS_FAN_CONFIG_12);
+		if (ret < 0)
+			return ret;
+
+		ret &= ~PB_FAN_1_INSTALLED;
+		ret = i2c_smbus_write_word_data(client, PMBUS_FAN_CONFIG_12,
+						ret);
+		if (ret < 0)
+			return ret;
+	}
+
+	return pmbus_do_probe(client, id, info);
+}
+
+static const struct i2c_device_id max31785_id[] = {
+	{ "max31785", 0 },
+	{ "max31785a", 0 },
+	{ },
+};
+
+MODULE_DEVICE_TABLE(i2c, max31785_id);
+
+static struct i2c_driver max31785_driver = {
+	.driver = {
+		.name = "max31785",
+	},
+	.probe = max31785_probe,
+	.remove = pmbus_do_remove,
+	.id_table = max31785_id,
+};
+
+module_i2c_driver(max31785_driver);
+
+MODULE_AUTHOR("Andrew Jeffery <andrew@xxxxxxxx>");
+MODULE_DESCRIPTION("PMBus driver for the Maxim MAX31785");
+MODULE_LICENSE("GPL");
-- 
2.11.0