diff --git a/Documentation/hwmon/max31785 b/Documentation/hwmon/max31785
index e9edbf11948f..8e75efc5e4b9 100644
--- a/Documentation/hwmon/max31785
+++ b/Documentation/hwmon/max31785
@@ -17,8 +17,9 @@ 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.
 
-For dual rotor fan configuration, the MAX31785 exposes the slowest rotor of the
-two in the fan[1-4]_input attributes.
+For dual-rotor configurations the MAX31785A exposes the second rotor tachometer
+readings in attributes fan[5-8]_input. By contrast the MAX31785 only exposes
+the slowest rotor measurement, and does so in the fan[1-4]_input attributes.
 
 Usage Notes
 -----------
@@ -31,7 +32,8 @@ Sysfs attributes
 
 fan[1-4]_alarm		Fan alarm.
 fan[1-4]_fault		Fan fault.
-fan[1-4]_input		Fan RPM.
+fan[1-8]_input		Fan RPM. On the MAX31785A, inputs 5-8 correspond to the
+			second rotor of fans 1-4
 fan[1-4]_target		Fan input target
 
 in[1-6]_crit		Critical maximum output voltage
diff --git a/drivers/hwmon/pmbus/max31785.c b/drivers/hwmon/pmbus/max31785.c
index 0d97ddf67079..2ca7febb2843 100644
--- a/drivers/hwmon/pmbus/max31785.c
+++ b/drivers/hwmon/pmbus/max31785.c
@@ -16,10 +16,82 @@
 
 enum max31785_regs {
 	MFR_REVISION		= 0x9b,
+	MFR_FAN_CONFIG		= 0xf1,
 };
 
+#define MAX31785			0x3030
+#define MAX31785A			0x3040
+
+#define MFR_FAN_CONFIG_DUAL_TACH	BIT(12)
+
 #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;
@@ -76,7 +148,25 @@ static int max31785_read_word_data(struct i2c_client *client, int page,
 	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;
@@ -85,10 +175,13 @@ static int max31785_read_word_data(struct i2c_client *client, int page,
 		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 = -ENODATA;
+		rv = (page >= MAX31785_NR_PAGES) ? -ENXIO : -ENODATA;
 		break;
 	}
 
@@ -100,6 +193,9 @@ 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))
@@ -127,7 +223,9 @@ 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,
@@ -174,6 +272,55 @@ static const struct pmbus_driver_info max31785_info = {
 	.func[22] = MAX31785_VOUT_FUNCS,
 };
 
+static int max31785_configure(struct i2c_client *client,
+			      const struct i2c_device_id *id,
+			      struct pmbus_driver_info *info)
+{
+	struct device *dev = &client->dev;
+	bool dual_tach = false;
+	int ret;
+	int i;
+
+	ret = i2c_smbus_read_word_data(client, MFR_REVISION);
+	if (ret < 0)
+		return ret;
+
+	if (!strcmp("max31785a", id->name)) {
+		if (ret == MAX31785A)
+			dual_tach = true;
+		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;
+	}
+
+	if (!dual_tach)
+		return 0;
+
+	for (i = 0; i <= 5; i++) {
+		ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, i);
+		if (ret < 0)
+			return ret;
+
+		ret = i2c_smbus_read_word_data(client, MFR_FAN_CONFIG);
+		if (ret < 0)
+			return ret;
+
+		if (ret & MFR_FAN_CONFIG_DUAL_TACH) {
+			int virtual = MAX31785_NR_PAGES + i;
+
+			info->pages = max(info->pages, virtual + 1);
+			info->func[virtual] |= PMBUS_HAVE_FAN12;
+			info->func[virtual] |= PMBUS_PAGE_VIRTUAL;
+		}
+	}
+
+	return 0;
+}
+
 static int max31785_probe(struct i2c_client *client,
 			  const struct i2c_device_id *id)
 {
@@ -181,6 +328,12 @@ static int max31785_probe(struct i2c_client *client,
 	struct pmbus_driver_info *info;
 	s64 ret;
 
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_BYTE_DATA |
+				     I2C_FUNC_SMBUS_WORD_DATA |
+				     I2C_FUNC_SMBUS_BLOCK_DATA))
+		return -ENODEV;
+
 	info = devm_kzalloc(dev, sizeof(struct pmbus_driver_info), GFP_KERNEL);
 	if (!info)
 		return -ENOMEM;
@@ -191,6 +344,10 @@ static int max31785_probe(struct i2c_client *client,
 	if (ret < 0)
 		return ret;
 
+	ret = max31785_configure(client, id, info);
+	if (ret < 0)
+		return ret;
+
 	return pmbus_do_probe(client, id, info);
 }
 
