[v2] hwmon: add driver for NZXT Kraken X42/X52/X62/X72

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index d4b422edbe3a..48bfa7887dd4 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -143,6 +143,7 @@  Hardware Monitoring Kernel Drivers
    npcm750-pwm-fan
    nsa320
    ntc_thermistor
+   nzxt-kraken2
    occ
    pc87360
    pc87427
diff --git a/Documentation/hwmon/nzxt-kraken2.rst b/Documentation/hwmon/nzxt-kraken2.rst
new file mode 100644
index 000000000000..94025de65a81
--- /dev/null
+++ b/Documentation/hwmon/nzxt-kraken2.rst
@@ -0,0 +1,42 @@ 
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver nzxt-kraken2
+==========================
+
+Supported devices:
+
+* NZXT Kraken X42
+* NZXT Kraken X52
+* NZXT Kraken X62
+* NZXT Kraken X72
+
+Author: Jonas Malaco
+
+Description
+-----------
+
+This driver enables hardware monitoring support for NZXT Kraken X42/X52/X62/X72
+all-in-one CPU liquid coolers.  Three sensors are available: fan speed, pump
+speed and coolant temperature.
+
+Fan and pump control, while supported by the firmware, are not currently
+exposed.  The addressable RGB LEDs, present in the integrated CPU water block
+and pump head, are not supported either.  But both features can be found in
+existing user-space tools (e.g. `liquidctl`_).
+
+.. _liquidctl: https://github.com/liquidctl/liquidctl
+
+Usage Notes
+-----------
+
+As these are USB HIDs, the driver can be loaded automatically by the kernel and
+supports hot swapping.
+
+Sysfs entries
+-------------
+
+=======================	========================================================
+fan1_input		Fan speed (in rpm)
+fan2_input		Pump speed (in rpm)
+temp1_input		Coolant temperature (in millidegrees Celsius)
+=======================	========================================================
diff --git a/MAINTAINERS b/MAINTAINERS
index 0635b30e467c..b8f9fc5eaf08 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12911,6 +12911,13 @@  L:	linux-nfc@lists.01.org (moderated for non-subscribers)
 S:	Supported
 F:	drivers/nfc/nxp-nci
 
+NZXT-KRAKEN2 HARDWARE MONITORING DRIVER
+M:	Jonas Malaco <jonas@protocubo.io>
+L:	linux-hwmon@vger.kernel.org
+S:	Maintained
+F:	Documentation/hwmon/nzxt-kraken2.rst
+F:	drivers/hwmon/nzxt-kraken2.c
+
 OBJAGG
 M:	Jiri Pirko <jiri@nvidia.com>
 L:	netdev@vger.kernel.org
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 54f04e61fb83..0ddc974b102e 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -1492,6 +1492,16 @@  config SENSORS_NSA320
 	  This driver can also be built as a module. If so, the module
 	  will be called nsa320-hwmon.
 
+config SENSORS_NZXT_KRAKEN2
+	tristate "NZXT Kraken X42/X51/X62/X72 liquid coolers"
+	depends on USB_HID
+	help
+	  If you say yes here you get support for hardware monitoring for the
+	  NZXT Kraken X42/X52/X62/X72 all-in-one CPU liquid coolers.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called nzxt-kraken2.
+
 source "drivers/hwmon/occ/Kconfig"
 
 config SENSORS_PCF8591
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index fe38e8a5c979..59e78bc212cf 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -155,6 +155,7 @@  obj-$(CONFIG_SENSORS_NCT7904)	+= nct7904.o
 obj-$(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_PC87360)	+= pc87360.o
 obj-$(CONFIG_SENSORS_PC87427)	+= pc87427.o
 obj-$(CONFIG_SENSORS_PCF8591)	+= pcf8591.o
diff --git a/drivers/hwmon/nzxt-kraken2.c b/drivers/hwmon/nzxt-kraken2.c
new file mode 100644
index 000000000000..a04892301a2c
--- /dev/null
+++ b/drivers/hwmon/nzxt-kraken2.c
@@ -0,0 +1,235 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * nzxt-kraken2.c - hwmon driver for NZXT Kraken X42/X52/X62/X72 coolers
+ *
+ * The device asynchronously sends HID reports (with id 0x04) twice a second to
+ * communicate current fan speed, pump speed and coolant temperature.  The
+ * device does not respond to Get_Report requests for this status report.
+ *
+ * Copyright 2019-2021  Jonas Malaco <jonas@protocubo.io>
+ */
+
+#include <asm/unaligned.h>
+#include <linux/hid.h>
+#include <linux/hwmon.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+
+#define STATUS_REPORT_ID	0x04
+#define STATUS_VALIDITY		2 /* seconds; equivalent to 4 missed updates */
+
+static const char *const kraken2_temp_label[] = {
+	"Coolant",
+};
+
+static const char *const kraken2_fan_label[] = {
+	"Fan",
+	"Pump",
+};
+
+struct kraken2_priv_data {
+	struct hid_device *hid_dev;
+	struct device *hwmon_dev;
+	s32 temp_input[1];
+	u16 fan_input[2];
+	unsigned long updated; /* jiffies */
+};
+
+static umode_t kraken2_is_visible(const void *data,
+				  enum hwmon_sensor_types type,
+				  u32 attr, int channel)
+{
+	return 0444;
+}
+
+static int kraken2_read(struct device *dev, enum hwmon_sensor_types type,
+			u32 attr, int channel, long *val)
+{
+	struct kraken2_priv_data *priv = dev_get_drvdata(dev);
+
+	if (time_after(jiffies, priv->updated + STATUS_VALIDITY * HZ))
+		return -ENODATA;
+
+	switch (type) {
+	case hwmon_temp:
+		*val = priv->temp_input[channel];
+		break;
+	case hwmon_fan:
+		*val = priv->fan_input[channel];
+		break;
+	default:
+		return -EOPNOTSUPP; /* unreachable */
+	}
+
+	return 0;
+}
+
+static int kraken2_read_string(struct device *dev, enum hwmon_sensor_types type,
+			       u32 attr, int channel, const char **str)
+{
+	switch (type) {
+	case hwmon_temp:
+		*str = kraken2_temp_label[channel];
+		break;
+	case hwmon_fan:
+		*str = kraken2_fan_label[channel];
+		break;
+	default:
+		return -EOPNOTSUPP; /* unreachable */
+	}
+	return 0;
+}
+
+static const struct hwmon_ops kraken2_hwmon_ops = {
+	.is_visible = kraken2_is_visible,
+	.read = kraken2_read,
+	.read_string = kraken2_read_string,
+};
+
+static const struct hwmon_channel_info *kraken2_info[] = {
+	HWMON_CHANNEL_INFO(temp,
+			   HWMON_T_INPUT | HWMON_T_LABEL),
+	HWMON_CHANNEL_INFO(fan,
+			   HWMON_F_INPUT | HWMON_F_LABEL,
+			   HWMON_F_INPUT | HWMON_F_LABEL),
+	NULL
+};
+
+static const struct hwmon_chip_info kraken2_chip_info = {
+	.ops = &kraken2_hwmon_ops,
+	.info = kraken2_info,
+};
+
+static int kraken2_raw_event(struct hid_device *hdev,
+			     struct hid_report *report, u8 *data, int size)
+{
+	struct kraken2_priv_data *priv;
+
+	if (size < 7 || report->id != STATUS_REPORT_ID)
+		return 0;
+
+	priv = hid_get_drvdata(hdev);
+
+	/*
+	 * The fractional byte of the coolant temperature has been observed to
+	 * be in the interval [1,9], but some of these steps are also
+	 * consistently skipped for certain integer parts.
+	 *
+	 * For the lack of a better idea, assume that the resolution is 0.1°C,
+	 * and that the missing steps are artifacts of how the firmware
+	 * processes the raw sensor data.
+	 */
+	priv->temp_input[0] = data[1] * 1000 + data[2] * 100;
+
+	priv->fan_input[0] = get_unaligned_be16(data + 3);
+	priv->fan_input[1] = get_unaligned_be16(data + 5);
+
+	priv->updated = jiffies;
+
+	return 0;
+}
+
+static int kraken2_probe(struct hid_device *hdev,
+			 const struct hid_device_id *id)
+{
+	struct kraken2_priv_data *priv;
+	int ret;
+
+	priv = devm_kzalloc(&hdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->hid_dev = hdev;
+	hid_set_drvdata(hdev, priv);
+
+	/*
+	 * Initialize ->updated to STATUS_VALIDITY seconds in the past, making
+	 * the initial empty data invalid for kraken2_read without the need for
+	 * a special case there.
+	 */
+	priv->updated = jiffies - STATUS_VALIDITY * HZ;
+
+	ret = hid_parse(hdev);
+	if (ret) {
+		hid_err(hdev, "hid parse failed with %d\n", ret);
+		return ret;
+	}
+
+	/*
+	 * Enable hidraw so existing user-space tools can continue to work.
+	 */
+	ret = hid_hw_start(hdev, HID_CONNECT_HIDRAW);
+	if (ret) {
+		hid_err(hdev, "hid hw start failed with %d\n", ret);
+		goto fail_and_stop;
+	}
+
+	ret = hid_hw_open(hdev);
+	if (ret) {
+		hid_err(hdev, "hid hw open failed with %d\n", ret);
+		goto fail_and_close;
+	}
+
+	priv->hwmon_dev = hwmon_device_register_with_info(&hdev->dev, "kraken2",
+							  priv, &kraken2_chip_info,
+							  NULL);
+	if (IS_ERR(priv->hwmon_dev)) {
+		ret = PTR_ERR(priv->hwmon_dev);
+		hid_err(hdev, "hwmon registration failed with %d\n", ret);
+		goto fail_and_close;
+	}
+
+	return 0;
+
+fail_and_close:
+	hid_hw_close(hdev);
+fail_and_stop:
+	hid_hw_stop(hdev);
+	return ret;
+}
+
+static void kraken2_remove(struct hid_device *hdev)
+{
+	struct kraken2_priv_data *priv = hid_get_drvdata(hdev);
+
+	hwmon_device_unregister(priv->hwmon_dev);
+
+	hid_hw_close(hdev);
+	hid_hw_stop(hdev);
+}
+
+static const struct hid_device_id kraken2_table[] = {
+	{ HID_USB_DEVICE(0x1e71, 0x170e) }, /* NZXT Kraken X42/X52/X62/X72 */
+	{ }
+};
+
+MODULE_DEVICE_TABLE(hid, kraken2_table);
+
+static struct hid_driver kraken2_driver = {
+	.name = "nzxt-kraken2",
+	.id_table = kraken2_table,
+	.probe = kraken2_probe,
+	.remove = kraken2_remove,
+	.raw_event = kraken2_raw_event,
+};
+
+static int __init kraken2_init(void)
+{
+	return hid_register_driver(&kraken2_driver);
+}
+
+static void __exit kraken2_exit(void)
+{
+	hid_unregister_driver(&kraken2_driver);
+}
+
+/*
+ * When compiled into the kernel, initialize after the hid bus.
+ */
+late_initcall(kraken2_init);
+module_exit(kraken2_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jonas Malaco <jonas@protocubo.io>");
+MODULE_DESCRIPTION("Hwmon driver for NZXT Kraken X42/X52/X62/X72 coolers");