hwmon: Add Nuvoton NCT7904 hwmon driver

The NCT7904D is a hardware monitor supporting up to 20 voltage sensors,
internal temperature sensor, Intel PECI and AMD SB-TSI CPU temperature
interface, up to 12 fan tachometer inputs, up to 4 fan control channels
with SmartFan.

Signed-off-by: Vadim V. Vlasov <vvlasov@dev.rtsoft.ru>
[Guenter Roeck: Fixed whitespace errors, dropped redundant comment]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

4 files changed, 663 insertions, 0 deletions

diff --git a/Documentation/hwmon/nct7904 b/Documentation/hwmon/nct7904
new file mode 100644
index 000000000000..014f112e2a14
--- /dev/null
+++ b/Documentation/hwmon/nct7904
@@ -0,0 +1,60 @@
+Kernel driver nct7904
+====================
+
+Supported chip:
+  * Nuvoton NCT7904D
+    Prefix: nct7904
+    Addresses: I2C 0x2d, 0x2e
+    Datasheet: Publicly available at Nuvoton website
+	http://www.nuvoton.com/
+
+Author: Vadim V. Vlasov <vvlasov@dev.rtsoft.ru>
+
+
+Description
+-----------
+
+The NCT7904D is a hardware monitor supporting up to 20 voltage sensors,
+internal temperature sensor, Intel PECI and AMD SB-TSI CPU temperature
+interface, up to 12 fan tachometer inputs, up to 4 fan control channels
+with SmartFan.
+
+
+Sysfs entries
+-------------
+
+Currently, the driver supports only the following features:
+
+in[1-20]_input		Input voltage measurements (mV)
+
+fan[1-12]_input		Fan tachometer measurements (rpm)
+
+temp1_input		Local temperature (1/1000 degree,
+			0.125 degree resolution)
+
+temp[2-9]_input		CPU temperatures (1/1000 degree,
+			0.125 degree resolution)
+
+fan[1-4]_mode		R/W, 0/1 for manual or SmartFan mode
+			Setting SmartFan mode is supported only if it has been
+			previously configured by BIOS (or configuration EEPROM)
+
+fan[1-4]_pwm		R/O in SmartFan mode, R/W in manual control mode
+
+The driver checks sensor control registers and does not export the sensors
+that are not enabled. Anyway, a sensor that is enabled may actually be not
+connected and thus provide zero readings.
+
+
+Limitations
+-----------
+
+The following features are not supported in current version:
+
+ - SmartFan control
+ - Watchdog
+ - GPIO
+ - external temperature sensors
+ - SMI
+ - min/max values
+ - many other...
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 4b40ea79b20f..2a5dd697c142 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -1145,6 +1145,16 @@ config SENSORS_NCT7802
 	  This driver can also be built as a module.  If so, the module
 	  will be called nct7802.
 
+config SENSORS_NCT7904
+	tristate "Nuvoton NCT7904"
+	depends on I2C
+	help
+	  If you say yes here you get support for the Nuvoton NCT7904
+	  hardware monitoring chip, including manual fan speed control.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called nct7904.
+
 config SENSORS_PCF8591
 	tristate "Philips PCF8591 ADC/DAC"
 	depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 6c941472e707..b4a40f17e2aa 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -120,6 +120,7 @@ obj-$(CONFIG_SENSORS_MENF21BMC_HWMON) += menf21bmc_hwmon.o
 obj-$(CONFIG_SENSORS_NCT6683)	+= nct6683.o
 obj-$(CONFIG_SENSORS_NCT6775)	+= nct6775.o
 obj-$(CONFIG_SENSORS_NCT7802)	+= nct7802.o
+obj-$(CONFIG_SENSORS_NCT7904)	+= nct7904.o
 obj-$(CONFIG_SENSORS_NTC_THERMISTOR)	+= ntc_thermistor.o
 obj-$(CONFIG_SENSORS_PC87360)	+= pc87360.o
 obj-$(CONFIG_SENSORS_PC87427)	+= pc87427.o
diff --git a/drivers/hwmon/nct7904.c b/drivers/hwmon/nct7904.c
new file mode 100644
index 000000000000..eaa8234e21d0
--- /dev/null
+++ b/drivers/hwmon/nct7904.c
@@ -0,0 +1,592 @@
+/*
+ * nct7904.c - driver for Nuvoton NCT7904D.
+ *
+ * Copyright (c) 2015 Kontron
+ * Author: Vadim V. Vlasov <vvlasov@dev.rtsoft.ru>
+ *
+ * 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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/i2c.h>
+#include <linux/mutex.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+
+#define VENDOR_ID_REG		0x7A	/* Any bank */
+#define NUVOTON_ID		0x50
+#define CHIP_ID_REG		0x7B	/* Any bank */
+#define NCT7904_ID		0xC5
+#define DEVICE_ID_REG		0x7C	/* Any bank */
+
+#define BANK_SEL_REG		0xFF
+#define BANK_0			0x00
+#define BANK_1			0x01
+#define BANK_2			0x02
+#define BANK_3			0x03
+#define BANK_4			0x04
+#define BANK_MAX		0x04
+
+#define FANIN_MAX		12	/* Counted from 1 */
+#define VSEN_MAX		21	/* VSEN1..14, 3VDD, VBAT, V3VSB,
+					   LTD (not a voltage), VSEN17..19 */
+#define FANCTL_MAX		4	/* Counted from 1 */
+#define TCPU_MAX		8	/* Counted from 1 */
+#define TEMP_MAX		4	/* Counted from 1 */
+
+#define VT_ADC_CTRL0_REG	0x20	/* Bank 0 */
+#define VT_ADC_CTRL1_REG	0x21	/* Bank 0 */
+#define VT_ADC_CTRL2_REG	0x22	/* Bank 0 */
+#define FANIN_CTRL0_REG		0x24
+#define FANIN_CTRL1_REG		0x25
+#define DTS_T_CTRL0_REG		0x26
+#define DTS_T_CTRL1_REG		0x27
+#define VT_ADC_MD_REG		0x2E
+
+#define VSEN1_HV_REG		0x40	/* Bank 0; 2 regs (HV/LV) per sensor */
+#define TEMP_CH1_HV_REG		0x42	/* Bank 0; same as VSEN2_HV */
+#define LTD_HV_REG		0x62	/* Bank 0; 2 regs in VSEN range */
+#define FANIN1_HV_REG		0x80	/* Bank 0; 2 regs (HV/LV) per sensor */
+#define T_CPU1_HV_REG		0xA0	/* Bank 0; 2 regs (HV/LV) per sensor */
+
+#define PRTS_REG		0x03	/* Bank 2 */
+#define FANCTL1_FMR_REG		0x00	/* Bank 3; 1 reg per channel */
+#define FANCTL1_OUT_REG		0x10	/* Bank 3; 1 reg per channel */
+
+static const unsigned short normal_i2c[] = {
+	0x2d, 0x2e, I2C_CLIENT_END
+};
+
+struct nct7904_data {
+	struct i2c_client *client;
+	struct mutex bank_lock;
+	int bank_sel;
+	u32 fanin_mask;
+	u32 vsen_mask;
+	u32 tcpu_mask;
+	u8 fan_mode[FANCTL_MAX];
+};
+
+/* Access functions */
+static int nct7904_bank_lock(struct nct7904_data *data, unsigned bank)
+{
+	int ret;
+
+	mutex_lock(&data->bank_lock);
+	if (data->bank_sel == bank)
+		return 0;
+	ret = i2c_smbus_write_byte_data(data->client, BANK_SEL_REG, bank);
+	if (ret == 0)
+		data->bank_sel = bank;
+	else
+		data->bank_sel = -1;
+	return ret;
+}
+
+static inline void nct7904_bank_release(struct nct7904_data *data)
+{
+	mutex_unlock(&data->bank_lock);
+}
+
+/* Read 1-byte register. Returns unsigned reg or -ERRNO on error. */
+static int nct7904_read_reg(struct nct7904_data *data,
+			    unsigned bank, unsigned reg)
+{
+	struct i2c_client *client = data->client;
+	int ret;
+
+	ret = nct7904_bank_lock(data, bank);
+	if (ret == 0)
+		ret = i2c_smbus_read_byte_data(client, reg);
+
+	nct7904_bank_release(data);
+	return ret;
+}
+
+/*
+ * Read 2-byte register. Returns register in big-endian format or
+ * -ERRNO on error.
+ */
+static int nct7904_read_reg16(struct nct7904_data *data,
+			      unsigned bank, unsigned reg)
+{
+	struct i2c_client *client = data->client;
+	int ret, hi;
+
+	ret = nct7904_bank_lock(data, bank);
+	if (ret == 0) {
+		ret = i2c_smbus_read_byte_data(client, reg);
+		if (ret >= 0) {
+			hi = ret;
+			ret = i2c_smbus_read_byte_data(client, reg + 1);
+			if (ret >= 0)
+				ret |= hi << 8;
+		}
+	}
+
+	nct7904_bank_release(data);
+	return ret;
+}
+
+/* Write 1-byte register. Returns 0 or -ERRNO on error. */
+static int nct7904_write_reg(struct nct7904_data *data,
+			     unsigned bank, unsigned reg, u8 val)
+{
+	struct i2c_client *client = data->client;
+	int ret;
+
+	ret = nct7904_bank_lock(data, bank);
+	if (ret == 0)
+		ret = i2c_smbus_write_byte_data(client, reg, val);
+
+	nct7904_bank_release(data);
+	return ret;
+}
+
+/* FANIN ATTR */
+static ssize_t show_fan(struct device *dev,
+			struct device_attribute *devattr, char *buf)
+{
+	int index = to_sensor_dev_attr(devattr)->index;
+	struct nct7904_data *data = dev_get_drvdata(dev);
+	int ret;
+	unsigned cnt, rpm;
+
+	ret = nct7904_read_reg16(data, BANK_0, FANIN1_HV_REG + index * 2);
+	if (ret < 0)
+		return ret;
+	cnt = ((ret & 0xff00) >> 3) | (ret & 0x1f);
+	if (cnt == 0x1fff)
+		rpm = 0;
+	else
+		rpm = 1350000 / cnt;
+	return sprintf(buf, "%u\n", rpm);
+}
+
+static umode_t nct7904_fanin_is_visible(struct kobject *kobj,
+					struct attribute *a, int n)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct nct7904_data *data = dev_get_drvdata(dev);
+
+	if (data->fanin_mask & (1 << n))
+		return a->mode;
+	return 0;
+}
+
+static SENSOR_DEVICE_ATTR(fan1_input, S_IRUGO, show_fan, NULL, 0);
+static SENSOR_DEVICE_ATTR(fan2_input, S_IRUGO, show_fan, NULL, 1);
+static SENSOR_DEVICE_ATTR(fan3_input, S_IRUGO, show_fan, NULL, 2);
+static SENSOR_DEVICE_ATTR(fan4_input, S_IRUGO, show_fan, NULL, 3);
+static SENSOR_DEVICE_ATTR(fan5_input, S_IRUGO, show_fan, NULL, 4);
+static SENSOR_DEVICE_ATTR(fan6_input, S_IRUGO, show_fan, NULL, 5);
+static SENSOR_DEVICE_ATTR(fan7_input, S_IRUGO, show_fan, NULL, 6);
+static SENSOR_DEVICE_ATTR(fan8_input, S_IRUGO, show_fan, NULL, 7);
+static SENSOR_DEVICE_ATTR(fan9_input, S_IRUGO, show_fan, NULL, 8);
+static SENSOR_DEVICE_ATTR(fan10_input, S_IRUGO, show_fan, NULL, 9);
+static SENSOR_DEVICE_ATTR(fan11_input, S_IRUGO, show_fan, NULL, 10);
+static SENSOR_DEVICE_ATTR(fan12_input, S_IRUGO, show_fan, NULL, 11);
+
+static struct attribute *nct7904_fanin_attrs[] = {
+	&sensor_dev_attr_fan1_input.dev_attr.attr,
+	&sensor_dev_attr_fan2_input.dev_attr.attr,
+	&sensor_dev_attr_fan3_input.dev_attr.attr,
+	&sensor_dev_attr_fan4_input.dev_attr.attr,
+	&sensor_dev_attr_fan5_input.dev_attr.attr,
+	&sensor_dev_attr_fan6_input.dev_attr.attr,
+	&sensor_dev_attr_fan7_input.dev_attr.attr,
+	&sensor_dev_attr_fan8_input.dev_attr.attr,
+	&sensor_dev_attr_fan9_input.dev_attr.attr,
+	&sensor_dev_attr_fan10_input.dev_attr.attr,
+	&sensor_dev_attr_fan11_input.dev_attr.attr,
+	&sensor_dev_attr_fan12_input.dev_attr.attr,
+	NULL
+};
+
+static const struct attribute_group nct7904_fanin_group = {
+	.attrs = nct7904_fanin_attrs,
+	.is_visible = nct7904_fanin_is_visible,
+};
+
+/* VSEN ATTR */
+static ssize_t show_voltage(struct device *dev,
+			    struct device_attribute *devattr, char *buf)
+{
+	int index = to_sensor_dev_attr(devattr)->index;
+	struct nct7904_data *data = dev_get_drvdata(dev);
+	int ret;
+	int volt;
+
+	ret = nct7904_read_reg16(data, BANK_0, VSEN1_HV_REG + index * 2);
+	if (ret < 0)
+		return ret;
+	volt = ((ret & 0xff00) >> 5) | (ret & 0x7);
+	if (index < 14)
+		volt *= 2; /* 0.002V scale */
+	else
+		volt *= 6; /* 0.006V scale */
+
+	return sprintf(buf, "%d\n", volt);
+}
+
+static ssize_t show_ltemp(struct device *dev,
+			  struct device_attribute *devattr, char *buf)
+{
+	struct nct7904_data *data = dev_get_drvdata(dev);
+	int ret;
+	int temp;
+
+	ret = nct7904_read_reg16(data, BANK_0, LTD_HV_REG);
+	if (ret < 0)
+		return ret;
+	temp = ((ret & 0xff00) >> 5) | (ret & 0x7);
+	temp = sign_extend32(temp, 10) * 125;
+
+	return sprintf(buf, "%d\n", temp);
+}
+
+static umode_t nct7904_vsen_is_visible(struct kobject *kobj,
+				       struct attribute *a, int n)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct nct7904_data *data = dev_get_drvdata(dev);
+
+	if (data->vsen_mask & (1 << n))
+		return a->mode;
+	return 0;
+}
+
+static SENSOR_DEVICE_ATTR(in1_input, S_IRUGO, show_voltage, NULL, 0);
+static SENSOR_DEVICE_ATTR(in2_input, S_IRUGO, show_voltage, NULL, 1);
+static SENSOR_DEVICE_ATTR(in3_input, S_IRUGO, show_voltage, NULL, 2);
+static SENSOR_DEVICE_ATTR(in4_input, S_IRUGO, show_voltage, NULL, 3);
+static SENSOR_DEVICE_ATTR(in5_input, S_IRUGO, show_voltage, NULL, 4);
+static SENSOR_DEVICE_ATTR(in6_input, S_IRUGO, show_voltage, NULL, 5);
+static SENSOR_DEVICE_ATTR(in7_input, S_IRUGO, show_voltage, NULL, 6);
+static SENSOR_DEVICE_ATTR(in8_input, S_IRUGO, show_voltage, NULL, 7);
+static SENSOR_DEVICE_ATTR(in9_input, S_IRUGO, show_voltage, NULL, 8);
+static SENSOR_DEVICE_ATTR(in10_input, S_IRUGO, show_voltage, NULL, 9);
+static SENSOR_DEVICE_ATTR(in11_input, S_IRUGO, show_voltage, NULL, 10);
+static SENSOR_DEVICE_ATTR(in12_input, S_IRUGO, show_voltage, NULL, 11);
+static SENSOR_DEVICE_ATTR(in13_input, S_IRUGO, show_voltage, NULL, 12);
+static SENSOR_DEVICE_ATTR(in14_input, S_IRUGO, show_voltage, NULL, 13);
+/*
+ * Next 3 voltage sensors have specific names in the Nuvoton doc
+ * (3VDD, VBAT, 3VSB) but we use vacant numbers for them.
+ */
+static SENSOR_DEVICE_ATTR(in15_input, S_IRUGO, show_voltage, NULL, 14);
+static SENSOR_DEVICE_ATTR(in16_input, S_IRUGO, show_voltage, NULL, 15);
+static SENSOR_DEVICE_ATTR(in20_input, S_IRUGO, show_voltage, NULL, 16);
+/* This is not a voltage, but a local temperature sensor. */
+static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, show_ltemp, NULL, 0);
+static SENSOR_DEVICE_ATTR(in17_input, S_IRUGO, show_voltage, NULL, 18);
+static SENSOR_DEVICE_ATTR(in18_input, S_IRUGO, show_voltage, NULL, 19);
+static SENSOR_DEVICE_ATTR(in19_input, S_IRUGO, show_voltage, NULL, 20);
+
+static struct attribute *nct7904_vsen_attrs[] = {
+	&sensor_dev_attr_in1_input.dev_attr.attr,
+	&sensor_dev_attr_in2_input.dev_attr.attr,
+	&sensor_dev_attr_in3_input.dev_attr.attr,
+	&sensor_dev_attr_in4_input.dev_attr.attr,
+	&sensor_dev_attr_in5_input.dev_attr.attr,
+	&sensor_dev_attr_in6_input.dev_attr.attr,
+	&sensor_dev_attr_in7_input.dev_attr.attr,
+	&sensor_dev_attr_in8_input.dev_attr.attr,
+	&sensor_dev_attr_in9_input.dev_attr.attr,
+	&sensor_dev_attr_in10_input.dev_attr.attr,
+	&sensor_dev_attr_in11_input.dev_attr.attr,
+	&sensor_dev_attr_in12_input.dev_attr.attr,
+	&sensor_dev_attr_in13_input.dev_attr.attr,
+	&sensor_dev_attr_in14_input.dev_attr.attr,
+	&sensor_dev_attr_in15_input.dev_attr.attr,
+	&sensor_dev_attr_in16_input.dev_attr.attr,
+	&sensor_dev_attr_in20_input.dev_attr.attr,
+	&sensor_dev_attr_temp1_input.dev_attr.attr,
+	&sensor_dev_attr_in17_input.dev_attr.attr,
+	&sensor_dev_attr_in18_input.dev_attr.attr,
+	&sensor_dev_attr_in19_input.dev_attr.attr,
+	NULL
+};
+
+static const struct attribute_group nct7904_vsen_group = {
+	.attrs = nct7904_vsen_attrs,
+	.is_visible = nct7904_vsen_is_visible,
+};
+
+/* CPU_TEMP ATTR */
+static ssize_t show_tcpu(struct device *dev,
+			 struct device_attribute *devattr, char *buf)
+{
+	int index = to_sensor_dev_attr(devattr)->index;
+	struct nct7904_data *data = dev_get_drvdata(dev);
+	int ret;
+	int temp;
+
+	ret = nct7904_read_reg16(data, BANK_0, T_CPU1_HV_REG + index * 2);
+	if (ret < 0)
+		return ret;
+
+	temp = ((ret & 0xff00) >> 5) | (ret & 0x7);
+	temp = sign_extend32(temp, 10) * 125;
+	return sprintf(buf, "%d\n", temp);
+}
+
+static umode_t nct7904_tcpu_is_visible(struct kobject *kobj,
+				       struct attribute *a, int n)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct nct7904_data *data = dev_get_drvdata(dev);
+
+	if (data->tcpu_mask & (1 << n))
+		return a->mode;
+	return 0;
+}
+
+/* "temp1_input" reserved for local temp */
+static SENSOR_DEVICE_ATTR(temp2_input, S_IRUGO, show_tcpu, NULL, 0);
+static SENSOR_DEVICE_ATTR(temp3_input, S_IRUGO, show_tcpu, NULL, 1);
+static SENSOR_DEVICE_ATTR(temp4_input, S_IRUGO, show_tcpu, NULL, 2);
+static SENSOR_DEVICE_ATTR(temp5_input, S_IRUGO, show_tcpu, NULL, 3);
+static SENSOR_DEVICE_ATTR(temp6_input, S_IRUGO, show_tcpu, NULL, 4);
+static SENSOR_DEVICE_ATTR(temp7_input, S_IRUGO, show_tcpu, NULL, 5);
+static SENSOR_DEVICE_ATTR(temp8_input, S_IRUGO, show_tcpu, NULL, 6);
+static SENSOR_DEVICE_ATTR(temp9_input, S_IRUGO, show_tcpu, NULL, 7);
+
+static struct attribute *nct7904_tcpu_attrs[] = {
+	&sensor_dev_attr_temp2_input.dev_attr.attr,
+	&sensor_dev_attr_temp3_input.dev_attr.attr,
+	&sensor_dev_attr_temp4_input.dev_attr.attr,
+	&sensor_dev_attr_temp5_input.dev_attr.attr,
+	&sensor_dev_attr_temp6_input.dev_attr.attr,
+	&sensor_dev_attr_temp7_input.dev_attr.attr,
+	&sensor_dev_attr_temp8_input.dev_attr.attr,
+	&sensor_dev_attr_temp9_input.dev_attr.attr,
+	NULL
+};
+
+static const struct attribute_group nct7904_tcpu_group = {
+	.attrs = nct7904_tcpu_attrs,
+	.is_visible = nct7904_tcpu_is_visible,
+};
+
+/* PWM ATTR */
+static ssize_t store_pwm(struct device *dev, struct device_attribute *devattr,
+			 const char *buf, size_t count)
+{
+	int index = to_sensor_dev_attr(devattr)->index;
+	struct nct7904_data *data = dev_get_drvdata(dev);
+	unsigned long val;
+	int ret;
+
+	if (kstrtoul(buf, 10, &val) < 0)
+		return -EINVAL;
+	if (val > 255)
+		return -EINVAL;
+
+	ret = nct7904_write_reg(data, BANK_3, FANCTL1_OUT_REG + index, val);
+
+	return ret ? ret : count;
+}
+
+static ssize_t show_pwm(struct device *dev,
+			struct device_attribute *devattr, char *buf)
+{
+	int index = to_sensor_dev_attr(devattr)->index;
+	struct nct7904_data *data = dev_get_drvdata(dev);
+	int val;
+
+	val = nct7904_read_reg(data, BANK_3, FANCTL1_OUT_REG + index);
+	if (val < 0)
+		return val;
+
+	return sprintf(buf, "%d\n", val);
+}
+
+static ssize_t store_mode(struct device *dev, struct device_attribute *devattr,
+			  const char *buf, size_t count)
+{
+	int index = to_sensor_dev_attr(devattr)->index;
+	struct nct7904_data *data = dev_get_drvdata(dev);
+	unsigned long val;
+	int ret;
+
+	if (kstrtoul(buf, 10, &val) < 0)
+		return -EINVAL;
+	if (val > 1 || (val && !data->fan_mode[index]))
+		return -EINVAL;
+
+	ret = nct7904_write_reg(data, BANK_3, FANCTL1_FMR_REG + index,
+				val ? data->fan_mode[index] : 0);
+
+	return ret ? ret : count;
+}
+
+/* Return 0 for manual mode or 1 for SmartFan mode */
+static ssize_t show_mode(struct device *dev,
+			 struct device_attribute *devattr, char *buf)
+{
+	int index = to_sensor_dev_attr(devattr)->index;
+	struct nct7904_data *data = dev_get_drvdata(dev);
+	int val;
+
+	val = nct7904_read_reg(data, BANK_3, FANCTL1_FMR_REG + index);
+	if (val < 0)
+		return val;
+
+	return sprintf(buf, "%d\n", val ? 1 : 0);
+}
+
+/* 2 attributes per channel: pwm and mode */
+static SENSOR_DEVICE_ATTR(fan1_pwm, S_IRUGO | S_IWUSR,
+			show_pwm, store_pwm, 0);
+static SENSOR_DEVICE_ATTR(fan1_mode, S_IRUGO | S_IWUSR,
+			show_mode, store_mode, 0);
+static SENSOR_DEVICE_ATTR(fan2_pwm, S_IRUGO | S_IWUSR,
+			show_pwm, store_pwm, 1);
+static SENSOR_DEVICE_ATTR(fan2_mode, S_IRUGO | S_IWUSR,
+			show_mode, store_mode, 1);
+static SENSOR_DEVICE_ATTR(fan3_pwm, S_IRUGO | S_IWUSR,
+			show_pwm, store_pwm, 2);
+static SENSOR_DEVICE_ATTR(fan3_mode, S_IRUGO | S_IWUSR,
+			show_mode, store_mode, 2);
+static SENSOR_DEVICE_ATTR(fan4_pwm, S_IRUGO | S_IWUSR,
+			show_pwm, store_pwm, 3);
+static SENSOR_DEVICE_ATTR(fan4_mode, S_IRUGO | S_IWUSR,
+			show_mode, store_mode, 3);
+
+static struct attribute *nct7904_fanctl_attrs[] = {
+	&sensor_dev_attr_fan1_pwm.dev_attr.attr,
+	&sensor_dev_attr_fan1_mode.dev_attr.attr,
+	&sensor_dev_attr_fan2_pwm.dev_attr.attr,
+	&sensor_dev_attr_fan2_mode.dev_attr.attr,
+	&sensor_dev_attr_fan3_pwm.dev_attr.attr,
+	&sensor_dev_attr_fan3_mode.dev_attr.attr,
+	&sensor_dev_attr_fan4_pwm.dev_attr.attr,
+	&sensor_dev_attr_fan4_mode.dev_attr.attr,
+	NULL
+};
+
+static const struct attribute_group nct7904_fanctl_group = {
+	.attrs = nct7904_fanctl_attrs,
+};
+
+static const struct attribute_group *nct7904_groups[] = {
+	&nct7904_fanin_group,
+	&nct7904_vsen_group,
+	&nct7904_tcpu_group,
+	&nct7904_fanctl_group,
+	NULL
+};
+
+/* Return 0 if detection is successful, -ENODEV otherwise */
+static int nct7904_detect(struct i2c_client *client,
+			  struct i2c_board_info *info)
+{
+	struct i2c_adapter *adapter = client->adapter;
+
+	if (!i2c_check_functionality(adapter,
+				     I2C_FUNC_SMBUS_READ_BYTE |
+				     I2C_FUNC_SMBUS_WRITE_BYTE_DATA))
+		return -ENODEV;
+
+	/* Determine the chip type. */
+	if (i2c_smbus_read_byte_data(client, VENDOR_ID_REG) != NUVOTON_ID ||
+	    i2c_smbus_read_byte_data(client, CHIP_ID_REG) != NCT7904_ID ||
+	    (i2c_smbus_read_byte_data(client, DEVICE_ID_REG) & 0xf0) != 0x50)
+		return -ENODEV;
+
+	strlcpy(info->type, "nct7904", I2C_NAME_SIZE);
+
+	return 0;
+}
+
+static int nct7904_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct nct7904_data *data;
+	struct device *hwmon_dev;
+	struct device *dev = &client->dev;
+	int ret, i;
+	u32 mask;
+
+	data = devm_kzalloc(dev, sizeof(struct nct7904_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->client = client;
+	mutex_init(&data->bank_lock);
+	data->bank_sel = -1;
+
+	/* Setup sensor groups. */
+	/* FANIN attributes */
+	ret = nct7904_read_reg16(data, BANK_0, FANIN_CTRL0_REG);
+	if (ret < 0)
+		return ret;
+	data->fanin_mask = (ret >> 8) | ((ret & 0xff) << 8);
+
+	/*
+	 * VSEN attributes
+	 *
+	 * Note: voltage sensors overlap with external temperature
+	 * sensors. So, if we ever decide to support the latter
+	 * we will have to adjust 'vsen_mask' accordingly.
+	 */
+	mask = 0;
+	ret = nct7904_read_reg16(data, BANK_0, VT_ADC_CTRL0_REG);
+	if (ret >= 0)
+		mask = (ret >> 8) | ((ret & 0xff) << 8);
+	ret = nct7904_read_reg(data, BANK_0, VT_ADC_CTRL2_REG);
+	if (ret >= 0)
+		mask |= (ret << 16);
+	data->vsen_mask = mask;
+
+	/* CPU_TEMP attributes */
+	ret = nct7904_read_reg16(data, BANK_0, DTS_T_CTRL0_REG);
+	if (ret < 0)
+		return ret;
+	data->tcpu_mask = ((ret >> 8) & 0xf) | ((ret & 0xf) << 4);
+
+	for (i = 0; i < FANCTL_MAX; i++) {
+		ret = nct7904_read_reg(data, BANK_3, FANCTL1_FMR_REG + i);
+		if (ret < 0)
+			return ret;
+		data->fan_mode[i] = ret;
+	}
+
+	hwmon_dev =
+		devm_hwmon_device_register_with_groups(dev, client->name, data,
+						       nct7904_groups);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id nct7904_id[] = {
+	{"nct7904", 0},
+	{}
+};
+
+static struct i2c_driver nct7904_driver = {
+	.class = I2C_CLASS_HWMON,
+	.driver = {
+		.name = "nct7904",
+	},
+	.probe = nct7904_probe,
+	.id_table = nct7904_id,
+	.detect = nct7904_detect,
+	.address_list = normal_i2c,
+};
+
+module_i2c_driver(nct7904_driver);
+
+MODULE_AUTHOR("Vadim V. Vlasov <vvlasov@dev.rtsoft.ru>");
+MODULE_DESCRIPTION("Hwmon driver for NUVOTON NCT7904");
+MODULE_LICENSE("GPL");