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, except the phase2 interrupt, 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.

It is not known how a forced system reset can be disabled on the
supported platforms. This means that the phase2 interrupt will only fire
at the same time as reset, so implementing phase2 is of little use.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/6d060bccbdcc709cfa79203485db85aad3c3beb5.1637252610.git.sander@svanheule.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

MAINTAINERS

@@ -16142,6 +16142,13 @@ 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:	drivers/watchdog/realtek_otto_wdt.c
+
 REALTEK RTL83xx SMI DSA ROUTER CHIPS
 M:	Linus Walleij <linus.walleij@linaro.org>
 S:	Maintained

drivers/watchdog/Kconfig

@@ -941,6 +941,19 @@ 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
+	depends on COMMON_CLK
+	select WATCHDOG_CORE
+	default MACH_REALTEK_RTL
+	help
+	  Say Y here to include support for the watchdog timer on Realtek
+	  RTL838x, RTL839x, RTL930x SoCs. This watchdog has pretimeout
+	  notifications and system reset on timeout.
+
+	  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

@@ -169,6 +169,7 @@ 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