diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
index 1443b3c..6b61084 100644
--- a/drivers/watchdog/at91sam9_wdt.c
+++ b/drivers/watchdog/at91sam9_wdt.c
@@ -10,9 +10,12 @@
  */
 
 /*
+ * For AT91SAM9x SoCs, the Watchdog Timer has the following constraint.
  * The Watchdog Timer Mode Register can be only written to once. If the
  * timeout need to be set from Linux, be sure that the bootstrap or the
  * bootloader doesn't write to this register.
+ * From SAMA5D4, the Watchdog Timer Mode Register can be written
+ * until a LOCKMR command is issued in WDT_CR.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
@@ -80,6 +83,11 @@ MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started "
 	"(default=" __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
 
 #define to_wdt(wdd) container_of(wdd, struct at91wdt, wdd)
+
+struct at91wdt_variant {
+	bool mr_writable;
+};
+
 struct at91wdt {
 	struct watchdog_device wdd;
 	void __iomem *base;
@@ -90,6 +98,9 @@ struct at91wdt {
 	unsigned long heartbeat;	/* WDT heartbeat in jiffies */
 	bool nowayout;
 	unsigned int irq;
+	bool use_timer;
+	bool enabled;
+	struct at91wdt_variant *drv_data;
 };
 
 /* ......................................................................... */
@@ -133,21 +144,67 @@ static void at91_ping(unsigned long data)
 static int at91_wdt_start(struct watchdog_device *wdd)
 {
 	struct at91wdt *wdt = to_wdt(wdd);
-	/* calculate when the next userspace timeout will be */
-	wdt->next_heartbeat = jiffies + wdd->timeout * HZ;
+	u32 reg;
+
+	if (wdt->drv_data->mr_writable) {
+		reg = wdt_read(wdt, AT91_WDT_MR);
+		reg &= ~AT91_WDT_WDDIS;
+		wdt_write(wdt, AT91_WDT_MR, reg);
+	} else {
+		/* calculate when the next userspace timeout will be */
+		wdt->next_heartbeat = jiffies + wdd->timeout * HZ;
+	}
+
 	return 0;
 }
 
 static int at91_wdt_stop(struct watchdog_device *wdd)
 {
-	/* The watchdog timer hardware can not be stopped... */
+	struct at91wdt *wdt = to_wdt(wdd);
+	u32 reg;
+
+	if (wdt->drv_data->mr_writable) {
+		reg = wdt_read(wdt, AT91_WDT_MR);
+		reg |= AT91_WDT_WDDIS;
+		wdt_write(wdt, AT91_WDT_MR, reg);
+	}
+
+	return 0;
+}
+
+static int at91_wdt_ping(struct watchdog_device *wdd)
+{
+	struct at91wdt *wdt = to_wdt(wdd);
+
+	wdt_write(wdt, AT91_WDT_CR, AT91_WDT_KEY | AT91_WDT_WDRSTT);
+
 	return 0;
 }
 
 static int at91_wdt_set_timeout(struct watchdog_device *wdd, unsigned int new_timeout)
 {
-	wdd->timeout = new_timeout;
-	return at91_wdt_start(wdd);
+	struct at91wdt *wdt = to_wdt(wdd);
+	u32 reg, timeout;
+
+	if (wdt->drv_data->mr_writable) {
+		timeout = secs_to_ticks(new_timeout);
+		if (timeout > WDT_COUNTER_MAX_TICKS)
+			return -EINVAL;
+
+		reg = wdt_read(wdt, AT91_WDT_MR);
+		reg &= ~AT91_WDT_WDV;
+		reg |= AT91_WDT_WDV_(timeout);
+		reg &= ~AT91_WDT_WDD;
+		reg |= AT91_WDT_WDD_(timeout);
+		wdt_write(wdt, AT91_WDT_MR, reg);
+
+		wdd->timeout = new_timeout;
+
+		return 0;
+	} else {
+		wdd->timeout = new_timeout;
+		return at91_wdt_start(wdd);
+	}
 }
 
 static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
@@ -161,50 +218,65 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
 	unsigned long max_heartbeat;
 	struct device *dev = &pdev->dev;
 
-	tmp = wdt_read(wdt, AT91_WDT_MR);
-	if ((tmp & mask) != (wdt->mr & mask)) {
-		if (tmp == WDT_MR_RESET) {
-			wdt_write(wdt, AT91_WDT_MR, wdt->mr);
-			tmp = wdt_read(wdt, AT91_WDT_MR);
+	if (wdt->drv_data->mr_writable) {
+		wdt->use_timer = false;
+
+		wdt_write(wdt, AT91_WDT_MR, wdt->mr | AT91_WDT_WDDIS);
+	} else {
+		wdt->use_timer = true;
+
+		tmp = wdt_read(wdt, AT91_WDT_MR);
+		if ((tmp & mask) != (wdt->mr & mask)) {
+			if (tmp == WDT_MR_RESET) {
+				wdt_write(wdt, AT91_WDT_MR, wdt->mr);
+				tmp = wdt_read(wdt, AT91_WDT_MR);
+			}
 		}
-	}
 
-	if (tmp & AT91_WDT_WDDIS) {
-		if (wdt->mr & AT91_WDT_WDDIS)
-			return 0;
-		dev_err(dev, "watchdog is disabled\n");
-		return -EINVAL;
+		if (tmp & AT91_WDT_WDDIS) {
+			if (wdt->mr & AT91_WDT_WDDIS)
+				return 0;
+
+			dev_err(dev, "watchdog is disabled\n");
+			return -EINVAL;
+		}
 	}
 
-	value = tmp & AT91_WDT_WDV;
-	delta = (tmp & AT91_WDT_WDD) >> 16;
+	tmp = wdt_read(wdt, AT91_WDT_MR);
+	wdt->enabled = (tmp & AT91_WDT_WDDIS) ? false : true;
 
-	if (delta < value)
-		min_heartbeat = ticks_to_hz_roundup(value - delta);
+	if (wdt->use_timer) {
+		value = tmp & AT91_WDT_WDV;
+		delta = (tmp & AT91_WDT_WDD) >> 16;
 
-	max_heartbeat = ticks_to_hz_rounddown(value);
-	if (!max_heartbeat) {
-		dev_err(dev,
-			"heartbeat is too small for the system to handle it correctly\n");
-		return -EINVAL;
-	}
+		if (delta < value)
+			min_heartbeat = ticks_to_hz_roundup(value - delta);
 
-	/*
-	 * Try to reset the watchdog counter 4 or 2 times more often than
-	 * actually requested, to avoid spurious watchdog reset.
-	 * If this is not possible because of the min_heartbeat value, reset
-	 * it at the min_heartbeat period.
-	 */
-	if ((max_heartbeat / 4) >= min_heartbeat)
-		wdt->heartbeat = max_heartbeat / 4;
-	else if ((max_heartbeat / 2) >= min_heartbeat)
-		wdt->heartbeat = max_heartbeat / 2;
-	else
-		wdt->heartbeat = min_heartbeat;
-
-	if (max_heartbeat < min_heartbeat + 4)
-		dev_warn(dev,
-			 "min heartbeat and max heartbeat might be too close for the system to handle it correctly\n");
+		max_heartbeat = ticks_to_hz_rounddown(value);
+		if (!max_heartbeat) {
+			dev_err(dev,
+				"heartbeat is too small for the system to handle it correctly\n");
+			return -EINVAL;
+		}
+
+		/*
+		 * Try to reset the watchdog counter 4 or 2 times more often than
+		 * actually requested, to avoid spurious watchdog reset.
+		 * If this is not possible because of the min_heartbeat value, reset
+		 * it at the min_heartbeat period.
+		 */
+		if ((max_heartbeat / 4) >= min_heartbeat)
+			wdt->heartbeat = max_heartbeat / 4;
+		else if ((max_heartbeat / 2) >= min_heartbeat)
+			wdt->heartbeat = max_heartbeat / 2;
+		else
+			wdt->heartbeat = min_heartbeat;
+
+		if (max_heartbeat < min_heartbeat + 4) {
+			dev_warn(dev,
+				 "min heartbeat and max heartbeat might be too close for the system to handle it correctly\n");
+		}
+	}
 
 	if ((tmp & AT91_WDT_WDFIEN) && wdt->irq) {
 		err = request_irq(wdt->irq, wdt_interrupt,
@@ -215,21 +287,24 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
 			return err;
 	}
 
-	if ((tmp & wdt->mr_mask) != (wdt->mr & wdt->mr_mask))
-		dev_warn(dev,
-			 "watchdog already configured differently (mr = %x expecting %x)\n",
-			 tmp & wdt->mr_mask, wdt->mr & wdt->mr_mask);
+	if (wdt->use_timer) {
+		if ((tmp & wdt->mr_mask) != (wdt->mr & wdt->mr_mask)) {
+			dev_warn(dev,
+				 "watchdog already configured differently (mr = %x expecting %x)\n",
+				 tmp & wdt->mr_mask, wdt->mr & wdt->mr_mask);
+		}
 
-	setup_timer(&wdt->timer, at91_ping, (unsigned long)wdt);
+		setup_timer(&wdt->timer, at91_ping, (unsigned long)wdt);
 
-	/*
-	 * Use min_heartbeat the first time to avoid spurious watchdog reset:
-	 * we don't know for how long the watchdog counter is running, and
-	 *  - resetting it right now might trigger a watchdog fault reset
-	 *  - waiting for heartbeat time might lead to a watchdog timeout
-	 *    reset
-	 */
-	mod_timer(&wdt->timer, jiffies + min_heartbeat);
+		/*
+		 * Use min_heartbeat the first time to avoid spurious watchdog reset:
+		 * we don't know for how long the watchdog counter is running, and
+		 *  - resetting it right now might trigger a watchdog fault reset
+		 *  - waiting for heartbeat time might lead to a watchdog timeout
+		 *    reset
+		 */
+		mod_timer(&wdt->timer, jiffies + min_heartbeat);
+	}
 
 	/* Try to set timeout from device tree first */
 	if (watchdog_init_timeout(&wdt->wdd, 0, dev))
@@ -239,12 +314,14 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
 	if (err)
 		goto out_stop_timer;
 
-	wdt->next_heartbeat = jiffies + wdt->wdd.timeout * HZ;
+	if (wdt->use_timer)
+		wdt->next_heartbeat = jiffies + wdt->wdd.timeout * HZ;
 
 	return 0;
 
 out_stop_timer:
-	del_timer(&wdt->timer);
+	if (wdt->use_timer)
+		del_timer(&wdt->timer);
 	return err;
 }
 
@@ -256,13 +333,54 @@ static const struct watchdog_info at91_wdt_info = {
 						WDIOF_MAGICCLOSE,
 };
 
-static const struct watchdog_ops at91_wdt_ops = {
+static struct watchdog_ops at91_wdt_ops = {
 	.owner =	THIS_MODULE,
 	.start =	at91_wdt_start,
 	.stop =		at91_wdt_stop,
 	.set_timeout =	at91_wdt_set_timeout,
 };
 
+static const struct at91wdt_variant drv_data_at91sam9260 = {
+	.mr_writable = false,
+};
+
+#if defined(CONFIG_OF)
+static const struct at91wdt_variant drv_data_sama5d4 = {
+	.mr_writable = true,
+};
+
+static const struct of_device_id at91_wdt_dt_ids[] = {
+	{ .compatible = "atmel,at91sam9260-wdt",
+	  .data = &drv_data_at91sam9260 },
+	{ .compatible = "atmel,sama5d4-wdt",
+	  .data = &drv_data_sama5d4 },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, at91_wdt_dt_ids);
+#endif
+
+static const struct platform_device_id at91wdt_ids[] = {
+	{
+		.name = "at91_wdt",
+		.driver_data = (unsigned long)&drv_data_at91sam9260,
+	},
+	{}
+};
+MODULE_DEVICE_TABLE(platform, at91wdt_ids);
+
+static struct at91wdt_variant *at91wdt_get_drv_data(struct platform_device *pdev)
+{
+	const struct of_device_id *match;
+
+	if (pdev->dev.of_node) {
+		match = of_match_node(at91_wdt_dt_ids, pdev->dev.of_node);
+		return (struct at91wdt_variant *)match->data;
+	} else {
+		return (struct at91wdt_variant *)
+			platform_get_device_id(pdev)->driver_data;
+	}
+}
+
 #if defined(CONFIG_OF)
 static int of_at91wdt_init(struct device_node *np, struct at91wdt *wdt)
 {
@@ -336,6 +454,10 @@ static int __init at91wdt_probe(struct platform_device *pdev)
 	if (!wdt)
 		return -ENOMEM;
 
+	wdt->drv_data = at91wdt_get_drv_data(pdev);
+	if (wdt->drv_data->mr_writable)
+		at91_wdt_ops.ping = at91_wdt_ping;
+
 	wdt->mr = (WDT_HW_TIMEOUT * 256) | AT91_WDT_WDRSTEN | AT91_WDT_WDD |
 		  AT91_WDT_WDDBGHLT | AT91_WDT_WDIDLEHLT;
 	wdt->mr_mask = 0x3FFFFFFF;
@@ -364,8 +486,12 @@ static int __init at91wdt_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, wdt);
 
-	pr_info("enabled (heartbeat=%d sec, nowayout=%d)\n",
-		wdt->wdd.timeout, wdt->nowayout);
+	if (wdt->enabled) {
+		dev_info(&pdev->dev, "enabled (heartbeat=%d sec, nowayout=%d)\n",
+			wdt->wdd.timeout, wdt->nowayout);
+	} else {
+		dev_info(&pdev->dev, "not enabled\n");
+	}
 
 	return 0;
 }
@@ -381,15 +507,6 @@ static int __exit at91wdt_remove(struct platform_device *pdev)
 	return 0;
 }
 
-#if defined(CONFIG_OF)
-static const struct of_device_id at91_wdt_dt_ids[] = {
-	{ .compatible = "atmel,at91sam9260-wdt" },
-	{ /* sentinel */ }
-};
-
-MODULE_DEVICE_TABLE(of, at91_wdt_dt_ids);
-#endif
-
 static struct platform_driver at91wdt_driver = {
 	.remove		= __exit_p(at91wdt_remove),
 	.driver		= {
diff --git a/drivers/watchdog/at91sam9_wdt.h b/drivers/watchdog/at91sam9_wdt.h
index c6fbb2e6..79add4f 100644
--- a/drivers/watchdog/at91sam9_wdt.h
+++ b/drivers/watchdog/at91sam9_wdt.h
@@ -22,11 +22,15 @@
 
 #define AT91_WDT_MR		0x04			/* Watchdog Mode Register */
 #define		AT91_WDT_WDV		(0xfff << 0)		/* Counter Value */
+#define			AT91_WDT_WDV_MSK	(0xfff)
+#define			AT91_WDT_WDV_(x)	(((x) & AT91_WDT_WDV_MSK) << 0)
 #define		AT91_WDT_WDFIEN		(1     << 12)		/* Fault Interrupt Enable */
 #define		AT91_WDT_WDRSTEN	(1     << 13)		/* Reset Processor */
 #define		AT91_WDT_WDRPROC	(1     << 14)		/* Timer Restart */
 #define		AT91_WDT_WDDIS		(1     << 15)		/* Watchdog Disable */
 #define		AT91_WDT_WDD		(0xfff << 16)		/* Delta Value */
+#define			AT91_WDT_WDD_MSK	(0xfff)
+#define			AT91_WDT_WDD_(x)	(((x) & AT91_WDT_WDD_MSK) << 16)
 #define		AT91_WDT_WDDBGHLT	(1     << 28)		/* Debug Halt */
 #define		AT91_WDT_WDIDLEHLT	(1     << 29)		/* Idle Halt */
 
