The MCU can be found on network-attached-storage devices made by QNAP
and provides access to fan control including reading back its RPM as
well as reading the temperature of the NAS case.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
  Documentation/hwmon/index.rst          |   1 +
  Documentation/hwmon/qnap-mcu-hwmon.rst |  27 ++
  MAINTAINERS                            |   1 +
  drivers/hwmon/Kconfig                  |  12 +
  drivers/hwmon/Makefile                 |   1 +
  drivers/hwmon/qnap-mcu-hwmon.c         | 392 +++++++++++++++++++++++++
  6 files changed, 434 insertions(+)
  create mode 100644 Documentation/hwmon/qnap-mcu-hwmon.rst
  create mode 100644 drivers/hwmon/qnap-mcu-hwmon.c

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 913c11390a457..7adbe23f06597 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst

@@ -199,6 +199,7 @@ Hardware Monitoring Kernel Drivers
     pxe1610
     pwm-fan
     q54sj108a2
+   qnap-mcu-hwmon
     raspberrypi-hwmon
     sbrmi
     sbtsi_temp

diff --git a/Documentation/hwmon/qnap-mcu-hwmon.rst b/Documentation/hwmon/qnap-mcu-hwmon.rst
new file mode 100644
index 0000000000000..83407e3408f2b
--- /dev/null
+++ b/Documentation/hwmon/qnap-mcu-hwmon.rst

@@ -0,0 +1,27 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver qnap-mcu-hwmon
+============================
+
+This driver enables the use of the hardware monitoring and fan control
+of the MCU used on some QNAP network attached storage devices.
+
+Author: Heiko Stuebner <heiko@sntech.de>
+
+Description
+-----------
+
+The driver implements a simple interface for driving the fan controlled by
+setting its PWM output value and exposes the fan rpm and case-temperature
+to user space through hwmon's sysfs interface.
+
+The fan rotation speed returned via the optional 'fan1_input' is calculated
+inside the MCU device.
+
+The driver provides the following sensor accesses in sysfs:
+
+=============== ======= =======================================================
+fan1_input	ro	fan tachometer speed in RPM
+pwm1		rw	relative speed (0-255), 255=max. speed.
+temp1_input	ro	Measured temperature in millicelsius
+=============== ======= =======================================================

diff --git a/MAINTAINERS b/MAINTAINERS
index baaec814bea1b..282042e3d5f80 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -18655,6 +18655,7 @@ F:	drivers/media/tuners/qm1d1c0042*
  QNAP MCU DRIVER
  M:	Heiko Stuebner <heiko@sntech.de>
  S:	Maintained
+F:	drivers/hwmon/qnap-mcu-hwmon.c
  F:	drivers/input/misc/qnap-mcu-input.c
  F:	drivers/leds/leds-qnap-mcu.c
  F:	drivers/mfd/qnap-mcu.c

diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index b60fe2e58ad6c..0118ad91057e0 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig

@@ -1793,6 +1793,18 @@ config SENSORS_PWM_FAN
  	  This driver can also be built as a module. If so, the module
  	  will be called pwm-fan.
  
+config SENSORS_QNAP_MCU_HWMON
+	tristate "QNAP MCU hardware monitoring"
+	depends on MFD_QNAP_MCU
+	depends on THERMAL || THERMAL=n
+	help
+	  Say yes here to enable support for fan and temperature sensor
+	  connected to a QNAP MCU, as found in a number of QNAP network
+	  attached storage devices.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called qnap-mcu-hwmon.
+
  config SENSORS_RASPBERRYPI_HWMON
  	tristate "Raspberry Pi voltage monitor"
  	depends on RASPBERRYPI_FIRMWARE || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)

diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index b1c7056c37db5..d60f46a03cc96 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile

@@ -187,6 +187,7 @@ obj-$(CONFIG_SENSORS_POWERZ)	+= powerz.o
  obj-$(CONFIG_SENSORS_POWR1220)  += powr1220.o
  obj-$(CONFIG_SENSORS_PT5161L)	+= pt5161l.o
  obj-$(CONFIG_SENSORS_PWM_FAN)	+= pwm-fan.o
+obj-$(CONFIG_SENSORS_QNAP_MCU_HWMON)	+= qnap-mcu-hwmon.o
  obj-$(CONFIG_SENSORS_RASPBERRYPI_HWMON)	+= raspberrypi-hwmon.o
  obj-$(CONFIG_SENSORS_SBTSI)	+= sbtsi_temp.o
  obj-$(CONFIG_SENSORS_SBRMI)	+= sbrmi.o

diff --git a/drivers/hwmon/qnap-mcu-hwmon.c b/drivers/hwmon/qnap-mcu-hwmon.c
new file mode 100644
index 0000000000000..f106fe8b012ea
--- /dev/null
+++ b/drivers/hwmon/qnap-mcu-hwmon.c

@@ -0,0 +1,392 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Driver for hwmon elements found on QNAP-MCU devices
+ *
+ * Copyright (C) 2024 Heiko Stuebner <heiko@sntech.de>
+ */
+
+#include <linux/fwnode.h>
+#include <linux/hwmon.h>
+#include <linux/mfd/qnap-mcu.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/thermal.h>
+
+struct qnap_mcu_hwmon {
+	struct qnap_mcu *mcu;
+	struct device *dev;
+
+	unsigned int pwm_min;
+	unsigned int pwm_max;
+
+	struct fwnode_handle *fan_node;
+	unsigned int fan_state;
+	unsigned int fan_max_state;
+	unsigned int *fan_cooling_levels;
+
+	struct thermal_cooling_device *cdev;
+	struct hwmon_chip_info info;
+};
+
+static int qnap_mcu_hwmon_get_rpm(struct qnap_mcu_hwmon *hwm)
+{
+	static const u8 cmd[] = {
+		[0] = 0x40, /* @ */
+		[1] = 0x46, /* F */
+		[2] = 0x41  /* A */
+	};
+	u8 reply[6];
+	int ret;
+
+	/* poll the fan rpm */
+	ret = qnap_mcu_exec(hwm->mcu, cmd, sizeof(cmd), reply, sizeof(reply));
+	if (ret)
+		return ret;
+
+	/* First 2 bytes must mirror the sent command */
+	if (memcmp(cmd, reply, 2))
+		return -EIO;
+
+	return reply[4] * 30;
+}
+
+static int qnap_mcu_hwmon_get_pwm(struct qnap_mcu_hwmon *hwm)
+{
+	static const u8 cmd[] = {
+		[0] = 0x40, /* @ */
+		[1] = 0x46, /* F */
+		[2] = 0x5a, /* Z */
+		[3] = 0x30  /* 0 ... fan-id? */
+	};
+	u8 reply[4];
+	int ret;
+
+	/* poll the fan pwm */
+	ret = qnap_mcu_exec(hwm->mcu, cmd, sizeof(cmd), reply, sizeof(reply));
+	if (ret)
+		return ret;
+
+	/* First 3 bytes must mirror the sent command */
+	if (memcmp(cmd, reply, 3))
+		return -EIO;
+
+	return reply[3];
+}
+
+static int qnap_mcu_hwmon_set_pwm(struct qnap_mcu_hwmon *hwm, u8 pwm)
+{
+	const u8 cmd[] = {
+		[0] = 0x40, /* @ */
+		[1] = 0x46, /* F */
+		[2] = 0x57, /* W */
+		[3] = 0x30, /* 0 ... fan-id? */
+		[4] = pwm
+	};
+
+	/* set the fan pwm */
+	return qnap_mcu_exec_with_ack(hwm->mcu, cmd, sizeof(cmd));
+}
+
+static int qnap_mcu_hwmon_get_temp(struct qnap_mcu_hwmon *hwm)
+{
+	static const u8 cmd[] = {
+		[0] = 0x40, /* @ */
+		[1] = 0x54, /* T */
+		[2] = 0x33  /* 3 */
+	};
+	u8 reply[4];
+	int ret;
+
+	/* poll the fan rpm */
+	ret = qnap_mcu_exec(hwm->mcu, cmd, sizeof(cmd), reply, sizeof(reply));
+	if (ret)
+		return ret;
+
+	/* First bytes must mirror the sent command */
+	if (memcmp(cmd, reply, sizeof(cmd)))
+		return -EIO;
+
+	/*
+	 * There is an unknown bit set in bit7.
+	 * Bits [6:0] report the actual temperature as returned by the
+	 * original qnap firmware-tools, so just drop bit7 for now.
+	 */
+	return (reply[3] & 0x7f) * 1000;
+}
+
+static int qnap_mcu_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
+				u32 attr, int channel, long val)
+{
+	struct qnap_mcu_hwmon *hwm = dev_get_drvdata(dev);
+
+	switch (attr) {
+	case hwmon_pwm_input:
+		if (val < 0 || val > 255)
+			return -EINVAL;
+
+		if (val != 0)
+			val = clamp_val(val, hwm->pwm_min, hwm->pwm_max);
+
+		return qnap_mcu_hwmon_set_pwm(hwm, val);
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return 0;
+}
+
+static int qnap_mcu_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
+			       u32 attr, int channel, long *val)
+{
+	struct qnap_mcu_hwmon *hwm = dev_get_drvdata(dev);
+	int ret;
+
+	switch (type) {
+	case hwmon_pwm:
+		switch (attr) {
+		case hwmon_pwm_input:
+			ret = qnap_mcu_hwmon_get_pwm(hwm);
+			if (ret < 0)
+				return ret;
+
+			*val = ret;
+			return 0;
+		default:
+			return -EOPNOTSUPP;
+		}
+	case hwmon_fan:
+		ret = qnap_mcu_hwmon_get_rpm(hwm);
+		if (ret < 0)
+			return ret;
+
+		*val = ret;
+		return 0;
+	case hwmon_temp:
+		ret = qnap_mcu_hwmon_get_temp(hwm);
+		if (ret < 0)
+			return ret;
+
+		*val = ret;
+		return 0;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static umode_t qnap_mcu_hwmon_is_visible(const void *data,
+					 enum hwmon_sensor_types type,
+					 u32 attr, int channel)
+{
+	switch (type) {
+	case hwmon_temp:
+		return 0444;
+
+	case hwmon_pwm:
+		return 0644;
+
+	case hwmon_fan:
+		return 0444;
+
+	default:
+		return 0;
+	}
+}
+
+static const struct hwmon_ops qnap_mcu_hwmon_hwmon_ops = {
+	.is_visible = qnap_mcu_hwmon_is_visible,
+	.read = qnap_mcu_hwmon_read,
+	.write = qnap_mcu_hwmon_write,
+};
+
+/* thermal cooling device callbacks */
+static int qnap_mcu_hwmon_get_max_state(struct thermal_cooling_device *cdev,
+					unsigned long *state)
+{
+	struct qnap_mcu_hwmon *hwm = cdev->devdata;
+
+	if (!hwm)
+		return -EINVAL;
+
+	*state = hwm->fan_max_state;
+
+	return 0;
+}
+
+static int qnap_mcu_hwmon_get_cur_state(struct thermal_cooling_device *cdev,
+					unsigned long *state)
+{
+	struct qnap_mcu_hwmon *hwm = cdev->devdata;
+
+	if (!hwm)
+		return -EINVAL;
+
+	*state = hwm->fan_state;
+
+	return 0;
+}
+
+static int qnap_mcu_hwmon_set_cur_state(struct thermal_cooling_device *cdev,
+					unsigned long state)
+{
+	struct qnap_mcu_hwmon *hwm = cdev->devdata;
+	int ret;
+
+	if (!hwm || state > hwm->fan_max_state)
+		return -EINVAL;
+
+	if (state == hwm->fan_state)
+		return 0;
+
+	ret = qnap_mcu_hwmon_set_pwm(hwm, hwm->fan_cooling_levels[state]);
+	if (ret)
+		return ret;
+
+	hwm->fan_state = state;
+
+	return ret;
+}
+
+static const struct thermal_cooling_device_ops qnap_mcu_hwmon_cooling_ops = {
+	.get_max_state = qnap_mcu_hwmon_get_max_state,
+	.get_cur_state = qnap_mcu_hwmon_get_cur_state,
+	.set_cur_state = qnap_mcu_hwmon_set_cur_state,
+};
+
+static void devm_fan_node_release(void *data)
+{
+	struct qnap_mcu_hwmon *hwm = data;
+
+	fwnode_handle_put(hwm->fan_node);
+}
+
+static int qnap_mcu_hwmon_get_cooling_data(struct device *dev, struct qnap_mcu_hwmon *hwm)
+{
+	struct fwnode_handle *fwnode;
+	int num, i, ret;
+
+	fwnode = device_get_named_child_node(dev->parent, "fan-0");