hwmon: Add Apple Silicon SMC hwmon driver

The System Management Controller on Apple Silicon devices is responsible
for integrating and exposing the data reported by the vast array of
hardware monitoring sensors present on these devices. It is also
responsible for fan control, and allows users to manually set fan
speeds if they so desire. Add a hwmon driver to expose current,
power, temperature, and voltage monitoring sensors, as well as
fan speed monitoring and control via the SMC on Apple Silicon devices.

The SMC firmware has no consistency between devices, even when they
share an SoC. The FourCC keys used to access sensors are almost
random. An M1 Mac mini will have different FourCCs for its CPU core
temperature sensors to an M1 MacBook Pro, for example. For this
reason, the valid sensors for a given device are specified in a
child of the SMC Devicetree node. The driver uses this information
to determine which sensors to make available at runtime.

Reviewed-by: Neal Gompa <neal@gompa.dev>
Co-developed-by: Janne Grunau <j@jannau.net>
Signed-off-by: James Calligeros <jcalligeros99@gmail.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Janne Grunau <j@jannau.net>

Author: chadmed

Documentation/hwmon/macsmc-hwmon.rst

@@ -0,0 +1,71 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+Kernel driver macsmc-hwmon
+==========================
+
+Supported hardware
+
+    * Apple Silicon Macs (M1 and up)
+
+Author: James Calligeros <jcalligeros99@gmail.com>
+
+Description
+-----------
+
+macsmc-hwmon exposes the Apple System Management controller's
+temperature, voltage, current and power sensors, as well as
+fan speed and control capabilities, via hwmon.
+
+Because each Apple Silicon Mac exposes a different set of sensors
+(e.g. the MacBooks expose battery telemetry that is not present on
+the desktop Macs), sensors present on any given machine are described
+via Devicetree. The driver picks these up and registers them with
+hwmon when probed.
+
+Manual fan speed is supported via the fan_control module parameter. This
+is disabled by default and marked as unsafe, as it cannot be proven that
+the system will fail safe if overheating due to manual fan control being
+used.
+
+sysfs interface
+---------------
+
+currX_input
+    Ammeter value
+
+currX_label
+    Ammeter label
+
+fanX_input
+    Current fan speed
+
+fanX_label
+    Fan label
+
+fanX_min
+    Minimum possible fan speed
+
+fanX_max
+    Maximum possible fan speed
+
+fanX_target
+    Current fan setpoint
+
+inX_input
+    Voltmeter value
+
+inX_label
+    Voltmeter label
+
+powerX_input
+    Power meter value
+
+powerX_label
+    Power meter label
+
+tempX_input
+    Temperature sensor value
+
+tempX_label
+    Temperature sensor label
+

MAINTAINERS

@@ -2445,12 +2445,14 @@ F:	Documentation/devicetree/bindings/rtc/apple,smc-rtc.yaml
 F:	Documentation/devicetree/bindings/spi/apple,spi.yaml
 F:	Documentation/devicetree/bindings/spmi/apple,spmi.yaml
 F:	Documentation/devicetree/bindings/watchdog/apple,wdt.yaml
+F:	Documentation/hwmon/macsmc-hwmon.rst
 F:	arch/arm64/boot/dts/apple/
 F:	drivers/bluetooth/hci_bcm4377.c
 F:	drivers/clk/clk-apple-nco.c
 F:	drivers/cpufreq/apple-soc-cpufreq.c
 F:	drivers/dma/apple-admac.c
 F:	drivers/gpio/gpio-macsmc.c
+F:	drivers/hwmon/macsmc-hwmon.c
 F:	drivers/pmdomain/apple/
 F:	drivers/i2c/busses/i2c-pasemi-core.c
 F:	drivers/i2c/busses/i2c-pasemi-platform.c

drivers/hwmon/Kconfig

@@ -1174,6 +1174,18 @@ config SENSORS_LTQ_CPUTEMP
 	  If you say yes here you get support for the temperature
 	  sensor inside your CPU.
 
+config SENSORS_MACSMC_HWMON
+	tristate "Apple SMC (Apple Silicon)"
+	depends on MFD_MACSMC && OF
+	help
+	  This driver enables hwmon support for current, power, temperature,
+	  and voltage sensors, as well as fan speed reporting and control
+	  on Apple Silicon devices. 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_MAX1111
 	tristate "Maxim MAX1111 Serial 8-bit ADC chip and compatibles"
 	depends on SPI_MASTER

drivers/hwmon/Makefile

@@ -148,6 +148,7 @@ 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-$(CONFIG_SENSORS_MACSMC_HWMON)	+= macsmc-hwmon.o
 obj-$(CONFIG_SENSORS_MAX1111)	+= max1111.o
 obj-$(CONFIG_SENSORS_MAX127)	+= max127.o
 obj-$(CONFIG_SENSORS_MAX16065)	+= max16065.o