mfd: Add core driver for Nuvoton NCT6694

The Nuvoton NCT6694 provides an USB interface to the host to
access its features.

Sub-devices can use the USB functions nct6694_read_msg() and
nct6694_write_msg() to issue a command. They can also request
interrupt that will be called when the USB device receives its
interrupt pipe.

Signed-off-by: Ming Yu <a0282524688@gmail.com>
Link: https://lore.kernel.org/r/20250912091952.1169369-2-a0282524688@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>

Author: m1ng1109

MAINTAINERS

@@ -18082,6 +18082,12 @@ F:	drivers/nubus/
 F:	include/linux/nubus.h
 F:	include/uapi/linux/nubus.h
 
+NUVOTON NCT6694 MFD DRIVER
+M:	Ming Yu <tmyu0@nuvoton.com>
+S:	Supported
+F:	drivers/mfd/nct6694.c
+F:	include/linux/mfd/nct6694.h
+
 NUVOTON NCT7201 IIO DRIVER
 M:	Eason Yang <j2anfernee@gmail.com>
 L:	linux-iio@vger.kernel.org

drivers/mfd/Kconfig

@@ -1134,6 +1134,21 @@ config MFD_MENF21BMC
 	  This driver can also be built as a module. If so the module
 	  will be called menf21bmc.
 
+config MFD_NCT6694
+	tristate "Nuvoton NCT6694 support"
+	select MFD_CORE
+	depends on USB
+	help
+	  This enables support for the Nuvoton USB device NCT6694, which shares
+	  peripherals.
+	  The Nuvoton NCT6694 is a peripheral expander with 16 GPIO chips,
+	  6 I2C controllers, 2 CANfd controllers, 2 Watchdog timers, ADC,
+	  PWM, and RTC.
+	  This driver provides core APIs to access the NCT6694 hardware
+	  monitoring and control features.
+	  Additional drivers must be enabled to utilize the specific
+	  functionalities of the device.
+
 config MFD_OCELOT
 	tristate "Microsemi Ocelot External Control Support"
 	depends on SPI_MASTER

drivers/mfd/Makefile

@@ -121,6 +121,8 @@ obj-$(CONFIG_MFD_MC13XXX)	+= mc13xxx-core.o
 obj-$(CONFIG_MFD_MC13XXX_SPI)	+= mc13xxx-spi.o
 obj-$(CONFIG_MFD_MC13XXX_I2C)	+= mc13xxx-i2c.o
 
+obj-$(CONFIG_MFD_NCT6694)	+= nct6694.o
+
 obj-$(CONFIG_MFD_CORE)		+= mfd-core.o
 
 ocelot-soc-objs			:= ocelot-core.o ocelot-spi.o