hwmon: add driver for the hwmon parts of qnap-mcu devices

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>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20241107114712.538976-8-heiko@sntech.de
Signed-off-by: Lee Jones <lee@kernel.org>

Documentation/hwmon/index.rst

@@ -201,6 +201,7 @@ Hardware Monitoring Kernel Drivers
    pxe1610
    pwm-fan
    q54sj108a2
+   qnap-mcu-hwmon
    raspberrypi-hwmon
    sbrmi
    sbtsi_temp

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
+=============== ======= =======================================================

MAINTAINERS

@@ -19108,6 +19108,7 @@ 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

drivers/hwmon/Kconfig

@@ -1822,6 +1822,18 @@ 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)

drivers/hwmon/Makefile

@@ -189,6 +189,7 @@ 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