mfd: Add Apple Silicon System Management Controller

The System Management Controller (SMC) on Apple Silicon machines is a
piece of hardware that exposes various functionalities such as
temperature sensors, voltage/power meters, shutdown/reboot handling,
GPIOs and more.

Communication happens via a shared mailbox using the RTKit protocol
which is also used for other co-processors. The SMC protocol then allows
reading and writing many different keys which implement the various
features. The MFD core device handles this protocol and exposes it
to the sub-devices.

Some of the sub-devices are potentially also useful on pre-M1 Apple
machines and support for SMCs on these machines can be added at a later
time.

Co-developed-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Signed-off-by: Sven Peter <sven@kernel.org>
Link: https://lore.kernel.org/r/20250610-smc-6-15-v7-5-556cafd771d3@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>

Author: svenpeter42

MAINTAINERS

@@ -2364,6 +2364,7 @@ F:	drivers/input/touchscreen/apple_z2.c
 F:	drivers/iommu/apple-dart.c
 F:	drivers/iommu/io-pgtable-dart.c
 F:	drivers/irqchip/irq-apple-aic.c
+F:	drivers/mfd/macsmc.c
 F:	drivers/nvme/host/apple.c
 F:	drivers/nvmem/apple-efuses.c
 F:	drivers/nvmem/apple-spmi-nvmem.c
@@ -2376,6 +2377,7 @@ F:	drivers/video/backlight/apple_dwi_bl.c
 F:	drivers/watchdog/apple_wdt.c
 F:	include/dt-bindings/interrupt-controller/apple-aic.h
 F:	include/dt-bindings/pinctrl/apple.h
+F:	include/linux/mfd/macsmc.h
 F:	include/linux/soc/apple/*
 F:	include/uapi/drm/asahi_drm.h
 

drivers/mfd/Kconfig

@@ -285,6 +285,24 @@ config MFD_CS42L43_SDW
 	  Select this to support the Cirrus Logic CS42L43 PC CODEC with
 	  headphone and class D speaker drivers over SoundWire.
 
+config MFD_MACSMC
+	tristate "Apple Silicon System Management Controller (SMC)"
+	depends on ARCH_APPLE || COMPILE_TEST
+	depends on OF
+	depends on APPLE_RTKIT
+	select MFD_CORE
+	help
+	  The System Management Controller (SMC) on Apple Silicon machines is a
+	  piece of hardware that exposes various functionalities such as
+	  temperature sensors, voltage/power meters, shutdown/reboot handling,
+	  GPIOs and more.
+
+	  Communication happens via a shared mailbox using the RTKit protocol
+	  which is also used for other co-processors. The SMC protocol then
+	  allows reading and writing many different keys which implement the
+	  various features. The MFD core device handles this protocol and
+	  exposes it to the sub-devices.
+
 config MFD_MADERA
 	tristate "Cirrus Logic Madera codecs"
 	select MFD_CORE

drivers/mfd/Makefile

@@ -21,6 +21,7 @@ obj-$(CONFIG_MFD_CS42L43_SDW)	+= cs42l43-sdw.o
 obj-$(CONFIG_MFD_ENE_KB3930)	+= ene-kb3930.o
 obj-$(CONFIG_MFD_EXYNOS_LPASS)	+= exynos-lpass.o
 obj-$(CONFIG_MFD_GATEWORKS_GSC)	+= gateworks-gsc.o
+obj-$(CONFIG_MFD_MACSMC)	+= macsmc.o
 
 obj-$(CONFIG_MFD_TI_LP873X)	+= lp873x.o
 obj-$(CONFIG_MFD_TI_LP87565)	+= lp87565.o