watchdog: Add Realtek Otto watchdog timer

Realtek MIPS SoCs (platform name Otto) have a watchdog timer with
pretimeout notifitication support. The WDT can (partially) hard reset,
or soft reset the SoC.

This driver implements all features as described in the devicetree
binding, and also functions as a restart handler. The cpu reset mode is
considered to be a "warm" restart, since this mode does not reset all
peripherals. Being an embedded system though, the "cpu" and "software"
modes will still cause the bootloader to run on restart.

Signed-off-by: Sander Vanheule <sander@svanheule.net>

MAINTAINERS

@@ -15862,6 +15862,13 @@ S:	Maintained
 F:	include/sound/rt*.h
 F:	sound/soc/codecs/rt*
 
+REALTEK OTTO WATCHDOG
+M:	Sander Vanheule <sander@svanheule.net>
+L:	linux-watchdog@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/watchdog/realtek,otto-wdt.yaml
+F:	driver/watchdog/realtek_otto_wdt.c
+
 REALTEK RTL83xx SMI DSA ROUTER CHIPS
 M:	Linus Walleij <linus.walleij@linaro.org>
 S:	Maintained

drivers/watchdog/Kconfig

@@ -954,6 +954,19 @@ config RTD119X_WATCHDOG
 	  Say Y here to include support for the watchdog timer in
 	  Realtek RTD1295 SoCs.
 
+config REALTEK_OTTO_WDT
+	tristate "Realtek Otto MIPS watchdog support"
+	depends on MACH_REALTEK_RTL || COMPILE_TEST
+	select COMMON_CLK
+	select WATCHDOG_CORE
+	default MACH_REALTEK_RTL
+	help
+	  Say Y here to include support for the watchdog timer on
+	  Realtek RTL838x, RTL839x SoCs. On timeout this watchdog
+	  will restart the system.
+
+	  When built as a module this will be called realtek_otto_wdt.
+
 config SPRD_WATCHDOG
 	tristate "Spreadtrum watchdog support"
 	depends on ARCH_SPRD || COMPILE_TEST

drivers/watchdog/Makefile

@@ -171,6 +171,7 @@ obj-$(CONFIG_IMGPDC_WDT) += imgpdc_wdt.o
 obj-$(CONFIG_MT7621_WDT) += mt7621_wdt.o
 obj-$(CONFIG_PIC32_WDT) += pic32-wdt.o
 obj-$(CONFIG_PIC32_DMT) += pic32-dmt.o
+obj-$(CONFIG_REALTEK_OTTO_WDT) += realtek_otto_wdt.o
 
 # PARISC Architecture