serial:sunplus-uart:Add Sunplus SoC UART Driver

Add Sunplus SoC UART Driver.
SP7021 UART block contains 5 UARTs.
There are UART0~4 that supported in SP7021, the features list as below.
Support Full-duplex communication.
Support data packet length configurable.
Support stop bit number configurable.
Support force break condition.
Support baud rate configurable.
Support error detection and report.
Support RXD Noise Rejection Vote configurable.

UART0 pinout only support TX/RX two pins.
UART1 to UART4 pinout support TX/RX/CTS/RTS four pins.
Normally UART0 used for kernel console, also can be used for normal uart.
Command line set "console=ttySUP0,115200", SUP means Sunplus Uart Port.
UART driver probe will create path named "/dev/ttySUPx".

https://sunplus.atlassian.net/wiki/spaces/doc/pages/1873412290/13.+Universal+Asynchronous+Receiver+Transmitter+UART

Signed-off-by: Hammer Hsieh <hammerh0314@gmail.com>

MAINTAINERS

@@ -18494,6 +18494,7 @@ SUNPLUS UART DRIVER
 M:	Hammer Hsieh <hammerh0314@gmail.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/serial/sunplus,sp7021-uart.yaml
+F:	drivers/tty/serial/sunplus-uart.c
 
 SUPERH
 M:	Yoshinori Sato <ysato@users.sourceforge.jp>

drivers/tty/serial/Kconfig

@@ -1562,6 +1562,31 @@ config SERIAL_LITEUART_CONSOLE
 	  and warnings and which allows logins in single user mode).
 	  Otherwise, say 'N'.
 
+config SERIAL_SUNPLUS
+	tristate "Sunplus UART support"
+	depends on OF || COMPILE_TEST
+	select SERIAL_CORE
+	help
+	  Select this option if you would like to use Sunplus serial port on
+	  Sunplus SoC SP7021.
+	  If you enable this option, Sunplus serial ports in the system will
+	  be registered as ttySUPx.
+	  This driver can also be built as a module. If so, the module will be
+	  called sunplus-uart.
+
+config SERIAL_SUNPLUS_CONSOLE
+	bool "Console on Sunplus UART"
+	depends on SERIAL_SUNPLUS
+	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
+	help
+	  Select this option if you would like to use a Sunplus UART as the
+	  system console.
+	  Even if you say Y here, the currently visible virtual console
+	  (/dev/tty0) will still be used as the system console by default, but
+	  you can alter that using a kernel command line option such as
+	  "console=ttySUPx".
+
 endmenu
 
 config SERIAL_MCTRL_GPIO

drivers/tty/serial/Makefile

@@ -87,6 +87,7 @@ obj-$(CONFIG_SERIAL_RDA)	+= rda-uart.o
 obj-$(CONFIG_SERIAL_MILBEAUT_USIO) += milbeaut_usio.o
 obj-$(CONFIG_SERIAL_SIFIVE)	+= sifive.o
 obj-$(CONFIG_SERIAL_LITEUART) += liteuart.o
+obj-$(CONFIG_SERIAL_SUNPLUS)	+= sunplus-uart.o
 
 # GPIOLIB helpers for modem control lines
 obj-$(CONFIG_SERIAL_MCTRL_GPIO)	+= serial_mctrl_gpio.o