hwmon: add driver for NZXT RGB&Fan Controller/Smart Device v2.

This driver implements monitoring and control of fans plugged into the
device. Besides typical speed monitoring and PWM duty cycle control,
voltage and current are reported for every fan.

The device also has 2 connectors for RGB LEDs, support for them isn't
implemented (mainly because there is no standardized sysfs interface).

Also, the device has a noise sensor, but the sensor seems to be completely
useless (and very imprecise), so support for it isn't implemented too.

The driver coexists with userspace tools that access the device through
hidraw interface with no known issues.

The driver has been tested on x86_64, built in and as a module.

Some changes/improvements were suggested by Jonas Malaco.

Signed-off-by: Aleksandr Mezin <mezin.alexander@gmail.com>
Link: https://lore.kernel.org/r/20211031033058.151014-1-mezin.alexander@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

6 files changed, 910 insertions, 0 deletions

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 284dfe20f8dc..df20022c741f 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -154,6 +154,7 @@ Hardware Monitoring Kernel Drivers
    nsa320
    ntc_thermistor
    nzxt-kraken2
+   nzxt-smart2
    occ
    pc87360
    pc87427
diff --git a/Documentation/hwmon/nzxt-smart2.rst b/Documentation/hwmon/nzxt-smart2.rst
new file mode 100644
index 000000000000..d9d1b2742665
--- /dev/null
+++ b/Documentation/hwmon/nzxt-smart2.rst
@@ -0,0 +1,62 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver nzxt-smart2
+=========================
+
+Supported devices:
+
+- NZXT RGB & Fan controller
+- NZXT Smart Device v2
+
+Description
+-----------
+
+This driver implements monitoring and control of fans plugged into the device.
+Besides typical speed monitoring and PWM duty cycle control, voltage and current
+is reported for every fan.
+
+The device also has two connectors for RGB LEDs; support for them isn't
+implemented (mainly because there is no standardized sysfs interface).
+
+Also, the device has a noise sensor, but the sensor seems to be completely
+useless (and very imprecise), so support for it isn't implemented too.
+
+Usage Notes
+-----------
+
+The device should be autodetected, and the driver should load automatically.
+
+If fans are plugged in/unplugged while the system is powered on, the driver
+must be reloaded to detect configuration changes; otherwise, new fans can't
+be controlled (`pwm*` changes will be ignored). It is necessary because the
+device has a dedicated "detect fans" command, and currently, it is executed only
+during initialization. Speed, voltage, current monitoring will work even without
+reload. As an alternative to reloading the module, a userspace tool (like
+`liquidctl`_) can be used to run "detect fans" command through hidraw interface.
+
+The driver coexists with userspace tools that access the device through hidraw
+interface with no known issues.
+
+.. _liquidctl: https://github.com/liquidctl/liquidctl
+
+Sysfs entries
+-------------
+
+=======================	========================================================
+fan[1-3]_input		Fan speed monitoring (in rpm).
+curr[1-3]_input		Current supplied to the fan (in milliamperes).
+in[0-2]_input		Voltage supplied to the fan (in millivolts).
+pwm[1-3]		Controls fan speed: PWM duty cycle for PWM-controlled
+			fans, voltage for other fans. Voltage can be changed in
+			9-12 V range, but the value of the sysfs attribute is
+			always in 0-255 range (1 = 9V, 255 = 12V). Setting the
+			attribute to 0 turns off the fan completely.
+pwm[1-3]_enable		1 if the fan can be controlled by writing to the
+			corresponding pwm* attribute, 0 otherwise. The device
+			can control only the fans it detected itself, so the
+			attribute is read-only.
+pwm[1-3]_mode		Read-only, 1 for PWM-controlled fans, 0 for other fans
+			(or if no fan connected).
+update_interval		The interval at which all inputs are updated (in
+			milliseconds). The default is 1000ms. Minimum is 250ms.
+=======================	========================================================
diff --git a/MAINTAINERS b/MAINTAINERS
index 5a00307d67e3..e7e40563498f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13805,6 +13805,13 @@ S:	Maintained
 F:	Documentation/hwmon/nzxt-kraken2.rst
 F:	drivers/hwmon/nzxt-kraken2.c
 
+NZXT-SMART2 HARDWARE MONITORING DRIVER
+M:	Aleksandr Mezin <mezin.alexander@gmail.com>
+L:	linux-hwmon@vger.kernel.org
+S:	Maintained
+F:	Documentation/hwmon/nzxt-smart2.rst
+F:	drivers/hwmon/nzxt-smart2.c
+
 OBJAGG
 M:	Jiri Pirko <jiri@nvidia.com>
 L:	netdev@vger.kernel.org
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 3e6064203d65..8df25f1079ba 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -1513,6 +1513,16 @@ config SENSORS_NZXT_KRAKEN2
 	  This driver can also be built as a module. If so, the module
 	  will be called nzxt-kraken2.
 
+config SENSORS_NZXT_SMART2
+	tristate "NZXT RGB & Fan Controller/Smart Device v2"
+	depends on USB_HID
+	help
+	  If you say yes here you get support for hardware monitoring for the
+	  NZXT RGB & Fan Controller/Smart Device v2.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called nzxt-smart2.
+
 source "drivers/hwmon/occ/Kconfig"
 
 config SENSORS_PCF8591
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 3a1551b3d570..185f946d698b 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -160,6 +160,7 @@ obj-$(CONFIG_SENSORS_NPCM7XX)	+= npcm750-pwm-fan.o
 obj-$(CONFIG_SENSORS_NSA320)	+= nsa320-hwmon.o
 obj-$(CONFIG_SENSORS_NTC_THERMISTOR)	+= ntc_thermistor.o
 obj-$(CONFIG_SENSORS_NZXT_KRAKEN2) += nzxt-kraken2.o
+obj-$(CONFIG_SENSORS_NZXT_SMART2) += nzxt-smart2.o
 obj-$(CONFIG_SENSORS_PC87360)	+= pc87360.o
 obj-$(CONFIG_SENSORS_PC87427)	+= pc87427.o
 obj-$(CONFIG_SENSORS_PCF8591)	+= pcf8591.o
diff --git a/drivers/hwmon/nzxt-smart2.c b/drivers/hwmon/nzxt-smart2.c
new file mode 100644
index 000000000000..534d39b8908e
--- /dev/null
+++ b/drivers/hwmon/nzxt-smart2.c
@@ -0,0 +1,829 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Reverse-engineered NZXT RGB & Fan Controller/Smart Device v2 driver.
+ *
+ * Copyright (c) 2021 Aleksandr Mezin
+ */
+
+#include <linux/hid.h>
+#include <linux/hwmon.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+#include <linux/wait.h>
+
+#include <asm/byteorder.h>
+#include <asm/unaligned.h>
+
+/*
+ * The device has only 3 fan channels/connectors. But all HID reports have
+ * space reserved for up to 8 channels.
+ */
+#define FAN_CHANNELS 3
+#define FAN_CHANNELS_MAX 8
+
+#define UPDATE_INTERVAL_DEFAULT_MS 1000
+
+/* These strings match labels on the device exactly */
+static const char *const fan_label[] = {
+	"FAN 1",
+	"FAN 2",
+	"FAN 3",
+};
+
+static const char *const curr_label[] = {
+	"FAN 1 Current",
+	"FAN 2 Current",
+	"FAN 3 Current",
+};
+
+static const char *const in_label[] = {
+	"FAN 1 Voltage",
+	"FAN 2 Voltage",
+	"FAN 3 Voltage",
+};
+
+enum {
+	INPUT_REPORT_ID_FAN_CONFIG = 0x61,
+	INPUT_REPORT_ID_FAN_STATUS = 0x67,
+};
+
+enum {
+	FAN_STATUS_REPORT_SPEED = 0x02,
+	FAN_STATUS_REPORT_VOLTAGE = 0x04,
+};
+
+enum {
+	FAN_TYPE_NONE = 0,
+	FAN_TYPE_DC = 1,
+	FAN_TYPE_PWM = 2,
+};
+
+struct unknown_static_data {
+	/*
+	 * Some configuration data? Stays the same after fan speed changes,
+	 * changes in fan configuration, reboots and driver reloads.
+	 *
+	 * The same data in multiple report types.
+	 *
+	 * Byte 12 seems to be the number of fan channels, but I am not sure.
+	 */
+	u8 unknown1[14];
+} __packed;
+
+/*
+ * The device sends this input report in response to "detect fans" command:
+ * a 2-byte output report { 0x60, 0x03 }.
+ */
+struct fan_config_report {
+	/* report_id should be INPUT_REPORT_ID_FAN_CONFIG = 0x61 */
+	u8 report_id;
+	/* Always 0x03 */
+	u8 magic;
+	struct unknown_static_data unknown_data;
+	/* Fan type as detected by the device. See FAN_TYPE_* enum. */
+	u8 fan_type[FAN_CHANNELS_MAX];
+} __packed;
+
+/*
+ * The device sends these reports at a fixed interval (update interval) -
+ * one report with type = FAN_STATUS_REPORT_SPEED, and one report with type =
+ * FAN_STATUS_REPORT_VOLTAGE per update interval.
+ */
+struct fan_status_report {
+	/* report_id should be INPUT_REPORT_ID_STATUS = 0x67 */
+	u8 report_id;
+	/* FAN_STATUS_REPORT_SPEED = 0x02 or FAN_STATUS_REPORT_VOLTAGE = 0x04 */
+	u8 type;
+	struct unknown_static_data unknown_data;
+	/* Fan type as detected by the device. See FAN_TYPE_* enum. */
+	u8 fan_type[FAN_CHANNELS_MAX];
+
+	union {
+		/* When type == FAN_STATUS_REPORT_SPEED */
+		struct {
+			/*
+			 * Fan speed, in RPM. Zero for channels without fans
+			 * connected.
+			 */
+			__le16 fan_rpm[FAN_CHANNELS_MAX];
+			/*
+			 * Fan duty cycle, in percent. Non-zero even for
+			 * channels without fans connected.
+			 */
+			u8 duty_percent[FAN_CHANNELS_MAX];
+			/*
+			 * Exactly the same values as duty_percent[], non-zero
+			 * for disconnected fans too.
+			 */
+			u8 duty_percent_dup[FAN_CHANNELS_MAX];
+			/* "Case Noise" in db */
+			u8 noise_db;
+		} __packed fan_speed;
+		/* When type == FAN_STATUS_REPORT_VOLTAGE */
+		struct {
+			/*
+			 * Voltage, in millivolts. Non-zero even when fan is
+			 * not connected.
+			 */
+			__le16 fan_in[FAN_CHANNELS_MAX];
+			/*
+			 * Current, in milliamperes. Near-zero when
+			 * disconnected.
+			 */
+			__le16 fan_current[FAN_CHANNELS_MAX];
+		} __packed fan_voltage;
+	} __packed;
+} __packed;
+
+#define OUTPUT_REPORT_SIZE 64
+
+enum {
+	OUTPUT_REPORT_ID_INIT_COMMAND = 0x60,
+	OUTPUT_REPORT_ID_SET_FAN_SPEED = 0x62,
+};
+
+enum {
+	INIT_COMMAND_SET_UPDATE_INTERVAL = 0x02,
+	INIT_COMMAND_DETECT_FANS = 0x03,
+};
+
+/*
+ * This output report sets pwm duty cycle/target fan speed for one or more
+ * channels.
+ */
+struct set_fan_speed_report {
+	/* report_id should be OUTPUT_REPORT_ID_SET_FAN_SPEED = 0x62 */
+	u8 report_id;
+	/* Should be 0x01 */
+	u8 magic;
+	/* To change fan speed on i-th channel, set i-th bit here */
+	u8 channel_bit_mask;
+	/*
+	 * Fan duty cycle/target speed in percent. For voltage-controlled fans,
+	 * the minimal voltage (duty_percent = 1) is about 9V.
+	 * Setting duty_percent to 0 (if the channel is selected in
+	 * channel_bit_mask) turns off the fan completely (regardless of the
+	 * control mode).
+	 */
+	u8 duty_percent[FAN_CHANNELS_MAX];
+} __packed;
+
+struct drvdata {
+	struct hid_device *hid;
+	struct device *hwmon;
+
+	u8 fan_duty_percent[FAN_CHANNELS];
+	u16 fan_rpm[FAN_CHANNELS];
+	bool pwm_status_received;
+
+	u16 fan_in[FAN_CHANNELS];
+	u16 fan_curr[FAN_CHANNELS];
+	bool voltage_status_received;
+
+	u8 fan_type[FAN_CHANNELS];
+	bool fan_config_received;
+
+	/*
+	 * wq is used to wait for *_received flags to become true.
+	 * All accesses to *_received flags and fan_* arrays are performed with
+	 * wq.lock held.
+	 */
+	wait_queue_head_t wq;
+	/*
+	 * mutex is used to:
+	 * 1) Prevent concurrent conflicting changes to update interval and pwm
+	 * values (after sending an output hid report, the corresponding field
+	 * in drvdata must be updated, and only then new output reports can be
+	 * sent).
+	 * 2) Synchronize access to output_buffer (well, the buffer is here,
+	 * because synchronization is necessary anyway - so why not get rid of
+	 * a kmalloc?).
+	 */
+	struct mutex mutex;
+	long update_interval;
+	u8 output_buffer[OUTPUT_REPORT_SIZE];
+};
+
+static long scale_pwm_value(long val, long orig_max, long new_max)
+{
+	if (val <= 0)
+		return 0;
+
+	/*
+	 * Positive values should not become zero: 0 completely turns off the
+	 * fan.
+	 */
+	return max(1L, DIV_ROUND_CLOSEST(min(val, orig_max) * new_max, orig_max));
+}
+
+static void handle_fan_config_report(struct drvdata *drvdata, void *data, int size)
+{
+	struct fan_config_report *report = data;
+	int i;
+
+	if (size < sizeof(struct fan_config_report))
+		return;
+
+	if (report->magic != 0x03)
+		return;
+
+	spin_lock(&drvdata->wq.lock);
+
+	for (i = 0; i < FAN_CHANNELS; i++)
+		drvdata->fan_type[i] = report->fan_type[i];
+
+	drvdata->fan_config_received = true;
+	wake_up_all_locked(&drvdata->wq);
+	spin_unlock(&drvdata->wq.lock);
+}
+
+static void handle_fan_status_report(struct drvdata *drvdata, void *data, int size)
+{
+	struct fan_status_report *report = data;
+	int i;
+
+	if (size < sizeof(struct fan_status_report))
+		return;
+
+	spin_lock(&drvdata->wq.lock);
+
+	/*
+	 * The device sends INPUT_REPORT_ID_FAN_CONFIG = 0x61 report in response
+	 * to "detect fans" command. Only accept other data after getting 0x61,
+	 * to make sure that fan detection is complete. In particular, fan
+	 * detection resets pwm values.
+	 */
+	if (!drvdata->fan_config_received) {
+		spin_unlock(&drvdata->wq.lock);
+		return;
+	}
+
+	for (i = 0; i < FAN_CHANNELS; i++) {
+		if (drvdata->fan_type[i] == report->fan_type[i])
+			continue;
+
+		/*
+		 * This should not happen (if my expectations about the device
+		 * are correct).
+		 *
+		 * Even if the userspace sends fan detect command through
+		 * hidraw, fan config report should arrive first.
+		 */
+		hid_warn_once(drvdata->hid,
+			      "Fan %d type changed unexpectedly from %d to %d",
+			      i, drvdata->fan_type[i], report->fan_type[i]);
+		drvdata->fan_type[i] = report->fan_type[i];
+	}
+
+	switch (report->type) {
+	case FAN_STATUS_REPORT_SPEED:
+		for (i = 0; i < FAN_CHANNELS; i++) {
+			drvdata->fan_rpm[i] =
+				get_unaligned_le16(&report->fan_speed.fan_rpm[i]);
+			drvdata->fan_duty_percent[i] =
+				report->fan_speed.duty_percent[i];
+		}
+
+		drvdata->pwm_status_received = true;
+		wake_up_all_locked(&drvdata->wq);
+		break;
+
+	case FAN_STATUS_REPORT_VOLTAGE:
+		for (i = 0; i < FAN_CHANNELS; i++) {
+			drvdata->fan_in[i] =
+				get_unaligned_le16(&report->fan_voltage.fan_in[i]);
+			drvdata->fan_curr[i] =
+				get_unaligned_le16(&report->fan_voltage.fan_current[i]);
+		}
+
+		drvdata->voltage_status_received = true;
+		wake_up_all_locked(&drvdata->wq);
+		break;
+	}
+
+	spin_unlock(&drvdata->wq.lock);
+}
+
+static umode_t nzxt_smart2_hwmon_is_visible(const void *data,
+					    enum hwmon_sensor_types type,
+					    u32 attr, int channel)
+{
+	switch (type) {
+	case hwmon_pwm:
+		switch (attr) {
+		case hwmon_pwm_input:
+		case hwmon_pwm_enable:
+			return 0644;
+
+		default:
+			return 0444;
+		}
+
+	case hwmon_chip:
+		switch (attr) {
+		case hwmon_chip_update_interval:
+			return 0644;
+
+		default:
+			return 0444;
+		}
+
+	default:
+		return 0444;
+	}
+}
+
+static int nzxt_smart2_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
+				  u32 attr, int channel, long *val)
+{
+	struct drvdata *drvdata = dev_get_drvdata(dev);
+	int res = -EINVAL;
+
+	if (type == hwmon_chip) {
+		switch (attr) {
+		case hwmon_chip_update_interval:
+			*val = drvdata->update_interval;
+			return 0;
+
+		default:
+			return -EINVAL;
+		}
+	}
+
+	spin_lock_irq(&drvdata->wq.lock);
+
+	switch (type) {
+	case hwmon_pwm:
+		/*
+		 * fancontrol:
+		 * 1) remembers pwm* values when it starts
+		 * 2) needs pwm*_enable to be 1 on controlled fans
+		 * So make sure we have correct data before allowing pwm* reads.
+		 * Returning errors for pwm of fan speed read can even cause
+		 * fancontrol to shut down. So the wait is unavoidable.
+		 */
+		switch (attr) {
+		case hwmon_pwm_enable:
+			res = wait_event_interruptible_locked_irq(drvdata->wq,
+								  drvdata->fan_config_received);
+			if (res)
+				goto unlock;
+
+			*val = drvdata->fan_type[channel] != FAN_TYPE_NONE;
+			break;
+
+		case hwmon_pwm_mode:
+			res = wait_event_interruptible_locked_irq(drvdata->wq,
+								  drvdata->fan_config_received);
+			if (res)
+				goto unlock;
+
+			*val = drvdata->fan_type[channel] == FAN_TYPE_PWM;
+			break;
+
+		case hwmon_pwm_input:
+			res = wait_event_interruptible_locked_irq(drvdata->wq,
+								  drvdata->pwm_status_received);
+			if (res)
+				goto unlock;
+
+			*val = scale_pwm_value(drvdata->fan_duty_percent[channel],
+					       100, 255);
+			break;
+		}
+		break;
+
+	case hwmon_fan:
+		/*
+		 * It's not strictly necessary to wait for *_received in the
+		 * remaining cases (fancontrol doesn't care about them). But I'm
+		 * doing it to have consistent behavior.
+		 */
+		if (attr == hwmon_fan_input) {
+			res = wait_event_interruptible_locked_irq(drvdata->wq,
+								  drvdata->pwm_status_received);
+			if (res)
+				goto unlock;
+
+			*val = drvdata->fan_rpm[channel];
+		}
+		break;
+
+	case hwmon_in:
+		if (attr == hwmon_in_input) {
+			res = wait_event_interruptible_locked_irq(drvdata->wq,
+								  drvdata->voltage_status_received);
+			if (res)
+				goto unlock;
+
+			*val = drvdata->fan_in[channel];
+		}
+		break;
+
+	case hwmon_curr:
+		if (attr == hwmon_curr_input) {
+			res = wait_event_interruptible_locked_irq(drvdata->wq,
+								  drvdata->voltage_status_received);
+			if (res)
+				goto unlock;
+
+			*val = drvdata->fan_curr[channel];
+		}
+		break;
+
+	default:
+		break;
+	}
+
+unlock:
+	spin_unlock_irq(&drvdata->wq.lock);
+	return res;
+}
+
+static int send_output_report(struct drvdata *drvdata, const void *data,
+			      size_t data_size)
+{
+	int ret;
+
+	if (data_size > sizeof(drvdata->output_buffer))
+		return -EINVAL;
+
+	memcpy(drvdata->output_buffer, data, data_size);
+
+	if (data_size < sizeof(drvdata->output_buffer))
+		memset(drvdata->output_buffer + data_size, 0,
+		       sizeof(drvdata->output_buffer) - data_size);
+
+	ret = hid_hw_output_report(drvdata->hid, drvdata->output_buffer,
+				   sizeof(drvdata->output_buffer));
+	return ret < 0 ? ret : 0;
+}
+
+static int set_pwm(struct drvdata *drvdata, int channel, long val)
+{
+	int ret;
+	u8 duty_percent = scale_pwm_value(val, 255, 100);
+
+	struct set_fan_speed_report report = {
+		.report_id = OUTPUT_REPORT_ID_SET_FAN_SPEED,
+		.magic = 1,
+		.channel_bit_mask = 1 << channel
+	};
+
+	ret = mutex_lock_interruptible(&drvdata->mutex);
+	if (ret)
+		return ret;
+
+	report.duty_percent[channel] = duty_percent;
+	ret = send_output_report(drvdata, &report, sizeof(report));
+	if (ret)
+		goto unlock;
+
+	/*
+	 * pwmconfig and fancontrol scripts expect pwm writes to take effect
+	 * immediately (i. e. read from pwm* sysfs should return the value
+	 * written into it). The device seems to always accept pwm values - even
+	 * when there is no fan connected - so update pwm status without waiting
+	 * for a report, to make pwmconfig and fancontrol happy. Worst case -
+	 * if the device didn't accept new pwm value for some reason (never seen
+	 * this in practice) - it will be reported incorrectly only until next
+	 * update. This avoids "fan stuck" messages from pwmconfig, and
+	 * fancontrol setting fan speed to 100% during shutdown.
+	 */
+	spin_lock_bh(&drvdata->wq.lock);
+	drvdata->fan_duty_percent[channel] = duty_percent;
+	spin_unlock_bh(&drvdata->wq.lock);
+
+unlock:
+	mutex_unlock(&drvdata->mutex);
+	return ret;
+}
+
+/*
+ * Workaround for fancontrol/pwmconfig trying to write to pwm*_enable even if it
+ * already is 1 and read-only. Otherwise, fancontrol won't restore pwm on
+ * shutdown properly.
+ */
+static int set_pwm_enable(struct drvdata *drvdata, int channel, long val)
+{
+	long expected_val;
+	int res;
+
+	spin_lock_irq(&drvdata->wq.lock);
+
+	res = wait_event_interruptible_locked_irq(drvdata->wq,
+						  drvdata->fan_config_received);
+	if (res) {
+		spin_unlock_irq(&drvdata->wq.lock);
+		return res;
+	}
+
+	expected_val = drvdata->fan_type[channel] != FAN_TYPE_NONE;
+
+	spin_unlock_irq(&drvdata->wq.lock);
+
+	return (val == expected_val) ? 0 : -EOPNOTSUPP;
+}
+
+/*
+ * Control byte	| Actual update interval in seconds
+ * 0xff		| 65.5
+ * 0xf7		| 63.46
+ * 0x7f		| 32.74
+ * 0x3f		| 16.36
+ * 0x1f		| 8.17
+ * 0x0f		| 4.07
+ * 0x07		| 2.02
+ * 0x03		| 1.00
+ * 0x02		| 0.744
+ * 0x01		| 0.488
+ * 0x00		| 0.25
+ */
+static u8 update_interval_to_control_byte(long interval)
+{
+	if (interval <= 250)
+		return 0;
+
+	return clamp_val(1 + DIV_ROUND_CLOSEST(interval - 488, 256), 0, 255);
+}
+
+static long control_byte_to_update_interval(u8 control_byte)
+{
+	if (control_byte == 0)
+		return 250;
+
+	return 488 + (control_byte - 1) * 256;
+}
+
+static int set_update_interval(struct drvdata *drvdata, long val)
+{
+	u8 control = update_interval_to_control_byte(val);
+	u8 report[] = {
+		OUTPUT_REPORT_ID_INIT_COMMAND,
+		INIT_COMMAND_SET_UPDATE_INTERVAL,
+		0x01,
+		0xe8,
+		control,
+		0x01,
+		0xe8,
+		control,
+	};
+	int ret;
+
+	ret = send_output_report(drvdata, report, sizeof(report));
+	if (ret)
+		return ret;
+
+	drvdata->update_interval = control_byte_to_update_interval(control);
+	return 0;
+}
+
+static int init_device(struct drvdata *drvdata, long update_interval)
+{
+	int ret;
+	u8 detect_fans_report[] = {
+		OUTPUT_REPORT_ID_INIT_COMMAND,
+		INIT_COMMAND_DETECT_FANS,
+	};
+
+	ret = send_output_report(drvdata, detect_fans_report,
+				 sizeof(detect_fans_report));
+	if (ret)
+		return ret;
+
+	return set_update_interval(drvdata, update_interval);
+}
+
+static int nzxt_smart2_hwmon_write(struct device *dev,
+				   enum hwmon_sensor_types type, u32 attr,
+				   int channel, long val)
+{
+	struct drvdata *drvdata = dev_get_drvdata(dev);
+	int ret;
+
+	switch (type) {
+	case hwmon_pwm:
+		switch (attr) {
+		case hwmon_pwm_enable:
+			return set_pwm_enable(drvdata, channel, val);
+
+		case hwmon_pwm_input:
+			return set_pwm(drvdata, channel, val);
+
+		default:
+			return -EINVAL;
+		}
+
+	case hwmon_chip:
+		switch (attr) {
+		case hwmon_chip_update_interval:
+			ret = mutex_lock_interruptible(&drvdata->mutex);
+			if (ret)
+				return ret;
+
+			ret = set_update_interval(drvdata, val);
+
+			mutex_unlock(&drvdata->mutex);
+			return ret;
+
+		default:
+			return -EINVAL;
+		}
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static int nzxt_smart2_hwmon_read_string(struct device *dev,
+					 enum hwmon_sensor_types type, u32 attr,
+					 int channel, const char **str)
+{
+	switch (type) {
+	case hwmon_fan:
+		*str = fan_label[channel];
+		return 0;
+	case hwmon_curr:
+		*str = curr_label[channel];
+		return 0;
+	case hwmon_in:
+		*str = in_label[channel];
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct hwmon_ops nzxt_smart2_hwmon_ops = {
+	.is_visible = nzxt_smart2_hwmon_is_visible,
+	.read = nzxt_smart2_hwmon_read,
+	.read_string = nzxt_smart2_hwmon_read_string,
+	.write = nzxt_smart2_hwmon_write,
+};
+
+static const struct hwmon_channel_info *nzxt_smart2_channel_info[] = {
+	HWMON_CHANNEL_INFO(fan, HWMON_F_INPUT | HWMON_F_LABEL,
+			   HWMON_F_INPUT | HWMON_F_LABEL,
+			   HWMON_F_INPUT | HWMON_F_LABEL),
+	HWMON_CHANNEL_INFO(pwm, HWMON_PWM_INPUT | HWMON_PWM_MODE | HWMON_PWM_ENABLE,
+			   HWMON_PWM_INPUT | HWMON_PWM_MODE | HWMON_PWM_ENABLE,
+			   HWMON_PWM_INPUT | HWMON_PWM_MODE | HWMON_PWM_ENABLE),
+	HWMON_CHANNEL_INFO(in, HWMON_I_INPUT | HWMON_I_LABEL,
+			   HWMON_I_INPUT | HWMON_I_LABEL,
+			   HWMON_I_INPUT | HWMON_I_LABEL),
+	HWMON_CHANNEL_INFO(curr, HWMON_C_INPUT | HWMON_C_LABEL,
+			   HWMON_C_INPUT | HWMON_C_LABEL,
+			   HWMON_C_INPUT | HWMON_C_LABEL),
+	HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
+	NULL
+};
+
+static const struct hwmon_chip_info nzxt_smart2_chip_info = {
+	.ops = &nzxt_smart2_hwmon_ops,
+	.info = nzxt_smart2_channel_info,
+};
+
+static int nzxt_smart2_hid_raw_event(struct hid_device *hdev,
+				     struct hid_report *report, u8 *data, int size)
+{
+	struct drvdata *drvdata = hid_get_drvdata(hdev);
+	u8 report_id = *data;
+
+	switch (report_id) {
+	case INPUT_REPORT_ID_FAN_CONFIG:
+		handle_fan_config_report(drvdata, data, size);
+		break;
+
+	case INPUT_REPORT_ID_FAN_STATUS:
+		handle_fan_status_report(drvdata, data, size);
+		break;
+	}
+
+	return 0;
+}
+
+static int nzxt_smart2_hid_reset_resume(struct hid_device *hdev)
+{
+	struct drvdata *drvdata = hid_get_drvdata(hdev);
+
+	/*
+	 * Userspace is still frozen (so no concurrent sysfs attribute access
+	 * is possible), but raw_event can already be called concurrently.
+	 */
+	spin_lock_bh(&drvdata->wq.lock);
+	drvdata->fan_config_received = false;
+	drvdata->pwm_status_received = false;
+	drvdata->voltage_status_received = false;
+	spin_unlock_bh(&drvdata->wq.lock);
+
+	return init_device(drvdata, drvdata->update_interval);
+}
+
+static int nzxt_smart2_hid_probe(struct hid_device *hdev,
+				 const struct hid_device_id *id)
+{
+	struct drvdata *drvdata;
+	int ret;
+
+	drvdata = devm_kzalloc(&hdev->dev, sizeof(struct drvdata), GFP_KERNEL);
+	if (!drvdata)
+		return -ENOMEM;
+
+	drvdata->hid = hdev;
+	hid_set_drvdata(hdev, drvdata);
+
+	init_waitqueue_head(&drvdata->wq);
+
+	mutex_init(&drvdata->mutex);
+	devm_add_action(&hdev->dev, (void (*)(void *))mutex_destroy,
+			&drvdata->mutex);
+
+	ret = hid_parse(hdev);
+	if (ret)
+		return ret;
+
+	ret = hid_hw_start(hdev, HID_CONNECT_HIDRAW);
+	if (ret)
+		return ret;
+
+	ret = hid_hw_open(hdev);
+	if (ret)
+		goto out_hw_stop;
+
+	hid_device_io_start(hdev);
+
+	init_device(drvdata, UPDATE_INTERVAL_DEFAULT_MS);
+
+	drvdata->hwmon =
+		hwmon_device_register_with_info(&hdev->dev, "nzxtsmart2", drvdata,
+						&nzxt_smart2_chip_info, NULL);
+	if (IS_ERR(drvdata->hwmon)) {
+		ret = PTR_ERR(drvdata->hwmon);
+		goto out_hw_close;
+	}
+
+	return 0;
+
+out_hw_close:
+	hid_hw_close(hdev);
+
+out_hw_stop:
+	hid_hw_stop(hdev);
+	return ret;
+}
+
+static void nzxt_smart2_hid_remove(struct hid_device *hdev)
+{
+	struct drvdata *drvdata = hid_get_drvdata(hdev);
+
+	hwmon_device_unregister(drvdata->hwmon);
+
+	hid_hw_close(hdev);
+	hid_hw_stop(hdev);
+}
+
+static const struct hid_device_id nzxt_smart2_hid_id_table[] = {
+	{ HID_USB_DEVICE(0x1e71, 0x2006) }, /* NZXT Smart Device V2 */
+	{ HID_USB_DEVICE(0x1e71, 0x200d) }, /* NZXT Smart Device V2 */
+	{ HID_USB_DEVICE(0x1e71, 0x2009) }, /* NZXT RGB & Fan Controller */
+	{ HID_USB_DEVICE(0x1e71, 0x200e) }, /* NZXT RGB & Fan Controller */
+	{ HID_USB_DEVICE(0x1e71, 0x2010) }, /* NZXT RGB & Fan Controller */
+	{},
+};
+
+static struct hid_driver nzxt_smart2_hid_driver = {
+	.name = "nzxt-smart2",
+	.id_table = nzxt_smart2_hid_id_table,
+	.probe = nzxt_smart2_hid_probe,
+	.remove = nzxt_smart2_hid_remove,
+	.raw_event = nzxt_smart2_hid_raw_event,
+#ifdef CONFIG_PM
+	.reset_resume = nzxt_smart2_hid_reset_resume,
+#endif
+};
+
+static int __init nzxt_smart2_init(void)
+{
+	return hid_register_driver(&nzxt_smart2_hid_driver);
+}
+
+static void __exit nzxt_smart2_exit(void)
+{
+	hid_unregister_driver(&nzxt_smart2_hid_driver);
+}
+
+MODULE_DEVICE_TABLE(hid, nzxt_smart2_hid_id_table);
+MODULE_AUTHOR("Aleksandr Mezin <mezin.alexander@gmail.com>");
+MODULE_DESCRIPTION("Driver for NZXT RGB & Fan Controller/Smart Device V2");
+MODULE_LICENSE("GPL");
+
+/*
+ * With module_init()/module_hid_driver() and the driver built into the kernel:
+ *
+ * Driver 'nzxt_smart2' was unable to register with bus_type 'hid' because the
+ * bus was not initialized.
+ */
+late_initcall(nzxt_smart2_init);
+module_exit(nzxt_smart2_exit);