i2c: Add driver for the RTL9300 I2C controller

Add support for the I2C controller on the RTL9300 SoC. There are two I2C
controllers in the RTL9300 that are part of the Ethernet switch register
block. Each of these controllers owns a SCL pin (GPIO8 for the fiorst
I2C controller, GPIO17 for the second). There are 8 possible SDA pins
(GPIO9-16) that can be assigned to either I2C controller. This
relationship is represented in the device tree with a child node for
each SDA line in use.

This is based on the openwrt implementation[1] but has been
significantly modified

[1] - https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/realtek/files-5.15/drivers/i2c/busses/i2c-rtl9300.c

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

Author: cpackham-atlnz

MAINTAINERS

@@ -20115,6 +20115,13 @@ S:	Maintained
 T:	git https://github.com/pkshih/rtw.git
 F:	drivers/net/wireless/realtek/rtl8xxxu/
 
+RTL9300 I2C DRIVER (rtl9300-i2c)
+M:	Chris Packham <chris.packham@alliedtelesis.co.nz>
+L:	linux-i2c@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/i2c/realtek,rtl9301-i2c.yaml
+F:	drivers/i2c/busses/i2c-rtl9300.c
+
 RTRS TRANSPORT DRIVERS
 M:	Md. Haris Iqbal <haris.iqbal@ionos.com>
 M:	Jack Wang <jinpu.wang@ionos.com>

drivers/i2c/busses/Kconfig

@@ -1053,6 +1053,16 @@ config I2C_RK3X
 	  This driver can also be built as a module. If so, the module will
 	  be called i2c-rk3x.
 
+config I2C_RTL9300
+	tristate "Realtek RTL9300 I2C controller"
+	depends on MACH_REALTEK_RTL || COMPILE_TEST
+	help
+	  Say Y here to include support for the I2C controller in Realtek
+	  RTL9300 SoCs.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called i2c-rtl9300.
+
 config I2C_RZV2M
 	tristate "Renesas RZ/V2M adapter"
 	depends on ARCH_RENESAS || COMPILE_TEST

drivers/i2c/busses/Makefile

@@ -100,6 +100,7 @@ obj-$(CONFIG_I2C_QCOM_GENI)	+= i2c-qcom-geni.o
 obj-$(CONFIG_I2C_QUP)		+= i2c-qup.o
 obj-$(CONFIG_I2C_RIIC)		+= i2c-riic.o
 obj-$(CONFIG_I2C_RK3X)		+= i2c-rk3x.o
+obj-$(CONFIG_I2C_RTL9300)	+= i2c-rtl9300.o
 obj-$(CONFIG_I2C_RZV2M)		+= i2c-rzv2m.o
 obj-$(CONFIG_I2C_S3C2410)	+= i2c-s3c2410.o
 obj-$(CONFIG_I2C_SH7760)	+= i2c-sh7760.o