serial: mvebu-uart: initial support for Armada-3700 serial port

Armada-3700's uart is a simple serial port, which doesn't
support. Configuring the modem control lines. The uart port has a 32
bytes Tx FIFO and a 64 bytes Rx FIFO

The uart driver implements the uart core operations. It also support the
system (early) console based on Armada-3700's serial port.

Known Issue:

The uart driver currently doesn't support clock programming, which means
the baud-rate stays with the default value configured by the bootloader
at boot time

[gregory.clement@free-electrons.com: Rewrite many part which are too long
to enumerate]

Signed-off-by: Wilson Ding <dingwei@marvell.com>
Signed-off-by: Nadav Haklai <nadavh@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/tty/serial/mvebu-uart.txt

@@ -0,0 +1,13 @@
+* Marvell UART : Non standard UART used in some of Marvell EBU SoCs (e.g., Armada-3700)
+
+Required properties:
+- compatible: "marvell,armada-3700-uart"
+- reg: offset and length of the register set for the device.
+- interrupts: device interrupt
+
+Example:
+	serial@12000 {
+		compatible = "marvell,armada-3700-uart";
+		reg = <0x12000 0x400>;
+		interrupts = <43>;
+	};

Documentation/kernel-parameters.txt

@@ -1058,6 +1058,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			A valid base address must be provided, and the serial
 			port must already be setup and configured.
 
+		armada3700_uart,<addr>
+			Start an early, polled-mode console on the
+			Armada 3700 serial port at the specified
+			address. The serial port must already be setup
+			and configured. Options are not yet supported.
+
 	earlyprintk=	[X86,SH,BLACKFIN,ARM,M68k]
 			earlyprintk=vga
 			earlyprintk=efi

drivers/tty/serial/Kconfig

@@ -1602,6 +1602,28 @@ config SERIAL_STM32_CONSOLE
 	depends on SERIAL_STM32=y
 	select SERIAL_CORE_CONSOLE
 
+config SERIAL_MVEBU_UART
+	bool "Marvell EBU serial port support"
+	select SERIAL_CORE
+	help
+	  This driver is for Marvell EBU SoC's UART. If you have a machine
+	  based on the Armada-3700 SoC and wish to use the on-board serial
+	  port,
+	  say 'Y' here.
+	  Otherwise, say 'N'.
+
+config SERIAL_MVEBU_CONSOLE
+	bool "Console on Marvell EBU serial port"
+	depends on SERIAL_MVEBU_UART
+	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
+	default y
+	help
+	  Say 'Y' here if you wish to use Armada-3700 UART as the system console.
+	  (the system console is the device which receives all kernel messages
+	  and warnings and which allows logins in single user mode)
+	  Otherwise, say 'N'.
+
 endmenu
 
 config SERIAL_MCTRL_GPIO

drivers/tty/serial/Makefile

@@ -90,6 +90,7 @@ obj-$(CONFIG_SERIAL_CONEXANT_DIGICOLOR)	+= digicolor-usart.o
 obj-$(CONFIG_SERIAL_MEN_Z135)	+= men_z135_uart.o
 obj-$(CONFIG_SERIAL_SPRD) += sprd_serial.o
 obj-$(CONFIG_SERIAL_STM32)	+= stm32-usart.o
+obj-$(CONFIG_SERIAL_MVEBU_UART)	+= mvebu-uart.o
 
 # GPIOLIB helpers for modem control lines
 obj-$(CONFIG_SERIAL_MCTRL_GPIO)	+= serial_mctrl_gpio.o