ath79: add support for Arduino Yun

Arduino Yun is a microcontroller development board, based on Atmel
ATmega32u4 and Atheros AR9331.

Specifications:
- MCU: ATmega32U4
- SoC: AR9331
- RAM: DDR2 64MB
- Flash: SPI NOR 16MB
- WiFi:
  - 2.4GHz: SoC internal
- Ethernet: 1x 10/100Mbps
- USB: 1x 2.0
- MicroSD: 1x SDHC

Notes:
- Stock firmware is based on OpenWrt AA.
- The SoC UART can be accessed only through the MCU.
  YunSerialTerminal is recommended for access to serial console.
- Stock firmware uses non-standard 250000 baudrate by default.
- The MCU can be reprogrammed from the SoC with avrdude linuxgpio.

Installation:
1.  Update U-Boot environment variables to adapt to new partition scheme.
    > setenv bootcmd "run addboard; run addtty; run addparts; run addrootfs; bootm 0x9f050000 || bootm 0x9fea0000"
    > setenv mtdparts "spi0.0:256k(u-boot)ro,64k(u-boot-env),15936k(firmware),64k(nvram),64k(art)ro"
    > saveenv
2.  Boot into stock firmware normally and perform sysupgrade with
    sysupgrade image.
    # sysupgrade -n -F /tmp/sysupgrade.bin

Signed-off-by: Sungbo Eo <mans0n@gorani.run>

1 files changed, 54 insertions, 0 deletions

diff --git a/target/linux/ath79/patches-5.4/921-serial-core-add-support-for-boot-console-with-arbitr.patch b/target/linux/ath79/patches-5.4/921-serial-core-add-support-for-boot-console-with-arbitr.patch
new file mode 100644
index 0000000000..dc863a511b
--- /dev/null
+++ b/target/linux/ath79/patches-5.4/921-serial-core-add-support-for-boot-console-with-arbitr.patch
@@ -0,0 +1,54 @@
+From 4d3c17975c7814884a721fe693b3adf5c426d759 Mon Sep 17 00:00:00 2001
+From: Hauke Mehrtens <hauke@hauke-m.de>
+Date: Tue, 10 Nov 2015 22:18:39 +0100
+Subject: [RFC] serial: core: add support for boot console with arbitrary
+ baud rates
+
+The Arduino Yun uses a baud rate of 250000 by default. The serial is
+going over the Atmel ATmega and is used to connect to this chip.
+Without this patch Linux wants to switch the console to 9600 Baud.
+
+With this patch Linux will use the configured baud rate and not a
+default one specified in uart_register_driver().
+
+Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
+[rebased to 4.14, slightly reworded commit message]
+Signed-off-by: Sungbo Eo <mans0n@gorani.run>
+---
+ drivers/tty/serial/serial_core.c | 6 +++++-
+ include/linux/console.h          | 1 +
+ 2 files changed, 6 insertions(+), 1 deletions(-)
+
+--- a/drivers/tty/serial/serial_core.c
++++ b/drivers/tty/serial/serial_core.c
+@@ -220,6 +220,8 @@ static int uart_port_startup(struct tty_
+ 	if (retval == 0) {
+ 		if (uart_console(uport) && uport->cons->cflag) {
+ 			tty->termios.c_cflag = uport->cons->cflag;
++			tty->termios.c_ospeed = uport->cons->baud;
++			tty->termios.c_ispeed = uport->cons->baud;
+ 			uport->cons->cflag = 0;
+ 		}
+ 		/*
+@@ -2104,8 +2106,10 @@ uart_set_options(struct uart_port *port,
+ 	 * Allow the setting of the UART parameters with a NULL console
+ 	 * too:
+ 	 */
+-	if (co)
++	if (co) {
+ 		co->cflag = termios.c_cflag;
++		co->baud = baud;
++	}
+ 
+ 	return 0;
+ }
+--- a/include/linux/console.h
++++ b/include/linux/console.h
+@@ -153,6 +153,7 @@ struct console {
+ 	short	flags;
+ 	short	index;
+ 	int	cflag;
++	int	baud;
+ 	void	*data;
+ 	struct	 console *next;
+ };