spi: spi-mem: Add Realtek SPI-NAND controller

Add a driver for the SPI-NAND controller on the RTL9300 family of
devices.

The controller supports
* Serial/Dual/Quad data with
* PIO and DMA data read/write operation
* Configurable flash access timing

There is a separate ECC controller on the RTL9300 which isn't currently
supported (instead we rely on the on-die ECC supported by most SPI-NAND
chips).

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Link: https://patch.msgid.link/20241015225434.3970360-4-chris.packham@alliedtelesis.co.nz
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: cpackham-atlnz

MAINTAINERS

@@ -19538,6 +19538,12 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/net/dsa/realtek.yaml
 F:	drivers/net/dsa/realtek/*
 
+REALTEK SPI-NAND
+M:	Chris Packham <chris.packham@alliedtelesis.co.nz>
+S:	Maintained
+F:	Documentation/devicetree/bindings/spi/realtek,rtl9301-snand.yaml
+F:	drivers/spi/spi-realtek-rtl-snand.c
+
 REALTEK WIRELESS DRIVER (rtlwifi family)
 M:	Ping-Ke Shih <pkshih@realtek.com>
 L:	linux-wireless@vger.kernel.org

drivers/spi/Kconfig

@@ -843,6 +843,17 @@ config SPI_PXA2XX
 config SPI_PXA2XX_PCI
 	def_tristate SPI_PXA2XX && PCI && COMMON_CLK
 
+config SPI_REALTEK_SNAND
+	tristate "Realtek SPI-NAND Flash Controller"
+	depends on MACH_REALTEK_RTL || COMPILE_TEST
+	select REGMAP
+	help
+	  This enables support for the SPI-NAND Flash controller on
+	  Realtek SoCs.
+
+	  This driver does not support generic SPI. The implementation
+	  only supports the spi-mem interface.
+
 config SPI_ROCKCHIP
 	tristate "Rockchip SPI controller driver"
 	depends on ARCH_ROCKCHIP || COMPILE_TEST

drivers/spi/Makefile

@@ -119,6 +119,7 @@ obj-$(CONFIG_SPI_ROCKCHIP)		+= spi-rockchip.o
 obj-$(CONFIG_SPI_ROCKCHIP_SFC)		+= spi-rockchip-sfc.o
 obj-$(CONFIG_SPI_RB4XX)			+= spi-rb4xx.o
 obj-$(CONFIG_MACH_REALTEK_RTL)		+= spi-realtek-rtl.o
+obj-$(CONFIG_SPI_REALTEK_SNAND)		+= spi-realtek-rtl-snand.o
 obj-$(CONFIG_SPI_RPCIF)			+= spi-rpc-if.o
 obj-$(CONFIG_SPI_RSPI)			+= spi-rspi.o
 obj-$(CONFIG_SPI_RZV2M_CSI)		+= spi-rzv2m-csi.o