RME: ath79: convert watchdog to panic instead of system reset

This works around apparent errors in how the watchdog's "full chip
reset" works.  Whether it be bootloader failure, or watchdog failure,
using the default full chip reset will occasionally result in the device
hanging on boot.  (Repeatedly seen on our carambola2 based devices, but
based the openwrt bugs, this has been intermittently seen on _many_
ath79 devices)

Fixes: https://dev.openwrt.org/ticket/12121
Uses the same fix as: https://dev.archive.openwrt.org/ticket/17839 (ie,
use a known fixed restart)
Further discussion and original implementation for ar71xx at: openwrt#747

Signed-off-by: Karl Palsson <karlp@etactica.com>

target/linux/ath79/patches-5.4/825-MIPS-ath79-watchdog-reliable-reboot.patch

@@ -0,0 +1,60 @@
+--- a/drivers/watchdog/ath79_wdt.c
++++ b/drivers/watchdog/ath79_wdt.c
+@@ -29,6 +29,7 @@
+ #include <linux/watchdog.h>
+ #include <linux/clk.h>
+ #include <linux/err.h>
++#include <linux/interrupt.h>
+ #include <linux/of.h>
+ #include <linux/of_platform.h>
+ #include <linux/uaccess.h>
+@@ -97,7 +98,11 @@ static inline void ath79_wdt_enable(void
+ 	 */
+ 	udelay(2);
+
+-	ath79_wdt_wr(WDOG_REG_CTRL, WDOG_CTRL_ACTION_FCR);
++	/*
++	 * Watchdog reset is unreliable, sometimes causing hangs.
++	 * Use GPI to trigger panic instead, which is well handled
++	 */
++	ath79_wdt_wr(WDOG_REG_CTRL, WDOG_CTRL_ACTION_GPI);
+ 	/* flush write */
+ 	ath79_wdt_rr(WDOG_REG_CTRL);
+ }
+@@ -248,10 +253,17 @@ static struct miscdevice ath79_wdt_miscd
+ 	.fops = &ath79_wdt_fops,
+ };
+
++static irqreturn_t ath79_wdt_interrupt(int irq, void *dev_id)
++{
++	/* Let the kernel handle watchdog failure instead */
++	panic("watchdog timeout, deferring to panic");
++}
++
+ static int ath79_wdt_probe(struct platform_device *pdev)
+ {
+ 	u32 ctrl;
+ 	int err;
++	struct resource *irq_res;
+
+ 	if (wdt_base)
+ 		return -EBUSY;
+@@ -282,6 +294,18 @@ static int ath79_wdt_probe(struct platfo
+ 			max_timeout, timeout);
+ 	}
+
++	irq_res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
++	if (!irq_res) {
++		dev_err(&pdev->dev, "no IRQ resource\n");
++		return -EINVAL;
++	}
++
++	err = request_irq(irq_res->start, ath79_wdt_interrupt, 0, DRIVER_NAME, NULL);
++	if (err) {
++		dev_err(&pdev->dev, "Failed to register wdt IRQ, err=%d\n", err);
++		goto err_clk_disable;
++	}
++
+ 	ctrl = ath79_wdt_rr(WDOG_REG_CTRL);
+ 	boot_status = (ctrl & WDOG_CTRL_LAST_RESET) ? WDIOF_CARDRESET : 0;
+