watchdog: aspeed: Allow configuring for alternate boot

Allow the device tree to specify a watchdog to fallover to
the alternate boot source.

The aspeeed watchdog can set a latch directing flash chip select 0 to
chip select 1, allowing boot from an alternate media if the watchdog
is not reset in time.  On the ast2400 bank 1 also goes to flash bank 1,
while on the ast2500 the chip selects are swapped.

Also clear the secondary boot bit during the machine restart operation.
Otherwise, the system will switch to the alternate boot after every
reboot, which is not desired.
Signed-off-by: NMilton Miller <miltonm@us.ibm.com>
Signed-off-by: NEddie James <eajames@linux.vnet.ibm.com>
Reviewed-by: NJoel Stanley <joel@jms.id.au>
Reviewed-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>

drivers/watchdog/aspeed_wdt.c

@@ -46,6 +46,7 @@ MODULE_DEVICE_TABLE(of, aspeed_wdt_of_table);
 #define WDT_RELOAD_VALUE	0x04
 #define WDT_RESTART		0x08
 #define WDT_CTRL		0x0C
+#define   WDT_CTRL_BOOT_SECONDARY	BIT(7)
 #define   WDT_CTRL_RESET_MODE_SOC	(0x00 << 5)
 #define   WDT_CTRL_RESET_MODE_FULL_CHIP	(0x01 << 5)
 #define   WDT_CTRL_RESET_MODE_ARM_CPU	(0x10 << 5)
@@ -158,6 +159,7 @@ static int aspeed_wdt_restart(struct watchdog_device *wdd,
 {
 	struct aspeed_wdt *wdt = to_aspeed_wdt(wdd);
 
+	wdt->ctrl &= ~WDT_CTRL_BOOT_SECONDARY;
 	aspeed_wdt_enable(wdt, 128 * WDT_RATE_1MHZ / 1000);
 
 	mdelay(1000);
@@ -242,6 +244,8 @@ static int aspeed_wdt_probe(struct platform_device *pdev)
 	}
 	if (of_property_read_bool(np, "aspeed,external-signal"))
 		wdt->ctrl |= WDT_CTRL_WDT_EXT;
+	if (of_property_read_bool(np, "aspeed,alt-boot"))
+		wdt->ctrl |= WDT_CTRL_BOOT_SECONDARY;
 
 	if (readl(wdt->base + WDT_CTRL) & WDT_CTRL_ENABLE)  {
 		/*