hwmon: add macsmc-hwmon driver

Apple Silicon devices, particularly Macs, continue Apple's tradition of
integrating a ridiculous number of sensors on their products. Most of these
report to the System Management Controller, and their data is exposed by
the SMC firmware as simple key-value pairs.

This commit adds an hwmon drive for retrieving the data reported by the
temperature, voltage, current and power sensors, as well as fan data.

Devices each expose their own unique set of sensors and fans, even with
the SMC being baked into the SoC. This driver walks a devicetree node
in order to discover the sensors present on the current device at runtime.

Co-developed-by: Janne Grunau <j@jannau.net>
Signed-off-by: Janne Grunau <j@jannau.net>
Signed-off-by: James Calligeros <jcalligeros99@gmail.com>

Author: chadmed

MAINTAINERS

@@ -2375,6 +2375,15 @@ F:	include/dt-bindings/pinctrl/apple.h
 F:	include/linux/soc/apple/*
 F:	include/uapi/drm/asahi_drm.h
 
+ARM/APPLE SMC HWMON DRIVER
+M:	James Calligeros <jcalligeros99@gmail.com>
+L:	asahi@lists.linux.dev
+S:	Maintained
+W:	https://asahilinux.org
+B:	https://github.com/AsahiLinux/linux/issues
+C:	irc://irc.oftc.net/asahi-dev
+F:	drivers/hwmon/macsmc-hwmon.c
+
 ARM/ARTPEC MACHINE SUPPORT
 M:	Jesper Nilsson <jesper.nilsson@axis.com>
 M:	Lars Persson <lars.persson@axis.com>

drivers/hwmon/Kconfig

@@ -1630,6 +1630,19 @@ config SENSORS_LM95245
 	  This driver can also be built as a module. If so, the module
 	  will be called lm95245.
 
+config SENSORS_MACSMC
+	tristate "Apple SMC (Apple Silicon)"
+	depends on APPLE_SMC && OF
+	depends on ARCH_APPLE && ARM64
+	help
+	  This driver exposes the temperature, voltage, current, power, and fan
+	  sensors present on Apple Silicon devices, such as the M-series Macs.
+
+	  Say Y here if you have an Apple Silicon device.
+
+	  This driver can also be built as a module. If so, the module will be called
+	  macsmc_hwmon.
+
 config SENSORS_PC87360
 	tristate "National Semiconductor PC87360 family"
 	depends on HAS_IOPORT

drivers/hwmon/Makefile

@@ -147,6 +147,7 @@ obj-$(CONFIG_SENSORS_LTC4260)	+= ltc4260.o
 obj-$(CONFIG_SENSORS_LTC4261)	+= ltc4261.o
 obj-$(CONFIG_SENSORS_LTC4282)	+= ltc4282.o
 obj-$(CONFIG_SENSORS_LTQ_CPUTEMP) += ltq-cputemp.o
+obj-$(CONFIG_SENSORS_MACSMC) += macsmc-hwmon.o
 obj-$(CONFIG_SENSORS_MAX1111)	+= max1111.o
 obj-$(CONFIG_SENSORS_MAX127)	+= max127.o
 obj-$(CONFIG_SENSORS_MAX16065)	+= max16065.o