Some firmwares describe WDAT registers inside memory ranges marked as
ACPI NVS in the E820 map, failing with -EBUSY during probe, leaving the
hardware watchdog unserviced and triggering periodic system resets.

This issue was observed on a OnLogic Karbon 524 device (when watchdog is
enabled in BIOS):

wdat_wdt wdat_wdt: error -EBUSY: can't request region for resource [mem 0x63df7a98]
wdat_wdt wdat_wdt: probe with driver wdat_wdt failed with error -16

This commit fixes this issue by falling back to devm_memremap() when
devm_ioremap_resource() fails with -EBUSY on an ACPI NVS region.

Signed-off-by: Renê de Souza Pinto <rene@renesp.com.br>
---
 drivers/watchdog/wdat_wdt.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/wdat_wdt.c b/drivers/watchdog/wdat_wdt.c
index dd3c2d69c9df..a56224cf8d22 100644
--- a/drivers/watchdog/wdat_wdt.c
+++ b/drivers/watchdog/wdat_wdt.c
@@ -7,7 +7,9 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/io.h>
 #include <linux/ioport.h>
+#include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/pm.h>
@@ -309,6 +311,33 @@ static struct watchdog_ops wdat_wdt_ops = {
 	.set_timeout = wdat_wdt_set_timeout,
 };
 
+static void __iomem *wdat_wdt_map_mem(struct device *dev, struct resource *res)
+{
+	resource_size_t size = resource_size(res);
+	void __iomem *reg;
+	void *addr;
+
+	/* Try standard reservation + ioremap first */
+	reg = devm_ioremap_resource(dev, res);
+	if (!IS_ERR(reg) || PTR_ERR(reg) != -EBUSY)
+		return reg;
+
+	/* If busy, check if conflict is due to ACPI NVS memory */
+	if (region_intersects(res->start, size, IORESOURCE_MEM,
+			      IORES_DESC_ACPI_NV_STORAGE) != REGION_INTERSECTS)
+		return reg; /* Real conflict, return -EBUSY */
+
+	dev_warn(dev, "%pR is inside ACPI NVS, mapping without reservation\n", res);
+
+	addr = devm_memremap(dev, res->start, size, MEMREMAP_WB);
+	if (IS_ERR(addr)) {
+		dev_err(dev, "failed to map resource %pR\n", res);
+		return IOMEM_ERR_PTR(PTR_ERR(addr));
+	}
+
+	return (void __iomem __force *)addr;
+}
+
 static int wdat_wdt_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -362,7 +391,7 @@ static int wdat_wdt_probe(struct platform_device *pdev)
 
 		res = &pdev->resource[i];
 		if (resource_type(res) == IORESOURCE_MEM) {
-			reg = devm_ioremap_resource(dev, res);
+			reg = wdat_wdt_map_mem(dev, res);
 			if (IS_ERR(reg)) {
 				ret = PTR_ERR(reg);
 				goto out_put_table;
-- 
2.53.0

Some firmwares describe WDAT registers inside memory ranges marked as
ACPI NVS in the E820 map, failing with -EBUSY during probe, leaving the
hardware watchdog unserviced and triggering periodic system resets.

This issue was observed on a OnLogic Karbon 524 device (when watchdog is
enabled in BIOS):

wdat_wdt wdat_wdt: error -EBUSY: can't request region for resource [mem 0x63df7a98]
wdat_wdt wdat_wdt: probe with driver wdat_wdt failed with error -16

Check whether the region falls inside ACPI NVS before requesting it and,
if so, map it without reservation.

Signed-off-by: Renê de Souza Pinto <rene@renesp.com.br>
---
 drivers/watchdog/wdat_wdt.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/wdat_wdt.c b/drivers/watchdog/wdat_wdt.c
index dd3c2d69c9df..55ea16e73652 100644
--- a/drivers/watchdog/wdat_wdt.c
+++ b/drivers/watchdog/wdat_wdt.c
@@ -7,7 +7,9 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/io.h>
 #include <linux/ioport.h>
+#include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/pm.h>
@@ -309,6 +311,29 @@ static struct watchdog_ops wdat_wdt_ops = {
 	.set_timeout = wdat_wdt_set_timeout,
 };
 
+static void __iomem *wdat_wdt_map_mem(struct device *dev, struct resource *res)
+{
+	resource_size_t size = resource_size(res);
+	void *addr;
+
+	/* Map memory region without reserving it if it falls inside ACPI NVS */
+	if (region_intersects(res->start, size, IORESOURCE_MEM,
+			      IORES_DESC_ACPI_NV_STORAGE) == REGION_INTERSECTS) {
+		dev_warn(dev, "%pR is inside ACPI NVS, mapping without reservation\n",
+			 res);
+
+		addr = devm_memremap(dev, res->start, size, MEMREMAP_WB);
+		if (IS_ERR(addr)) {
+			dev_err(dev, "failed to map resource %pR\n", res);
+			return IOMEM_ERR_PTR(PTR_ERR(addr));
+		}
+
+		return (void __iomem __force *)addr;
+	}
+
+	return devm_ioremap_resource(dev, res);
+}
+
 static int wdat_wdt_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -362,7 +387,7 @@ static int wdat_wdt_probe(struct platform_device *pdev)
 
 		res = &pdev->resource[i];
 		if (resource_type(res) == IORESOURCE_MEM) {
-			reg = devm_ioremap_resource(dev, res);
+			reg = wdat_wdt_map_mem(dev, res);
 			if (IS_ERR(reg)) {
 				ret = PTR_ERR(reg);
 				goto out_put_table;
-- 
2.53.0

On Tue, Aug 04, 2026 at 12:39:57PM +0200, Renê de Souza Pinto wrote:
> Some firmwares describe WDAT registers inside memory ranges marked as
> ACPI NVS in the E820 map, failing with -EBUSY during probe, leaving the
> hardware watchdog unserviced and triggering periodic system resets.
> 
> This issue was observed on a OnLogic Karbon 524 device (when watchdog is
> enabled in BIOS):
> 
> wdat_wdt wdat_wdt: error -EBUSY: can't request region for resource [mem 0x63df7a98]
> wdat_wdt wdat_wdt: probe with driver wdat_wdt failed with error -16
> 
> Check whether the region falls inside ACPI NVS before requesting it and,
> if so, map it without reservation.
> 
> Signed-off-by: Renê de Souza Pinto <rene@renesp.com.br>

Applied.

Thanks,
Guenter