linux-kernel - [PATCH] watchdog: Always return time left until watchdog times out

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Message-ID: <20251118210407.2362338-1-linux@roeck-us.net>
Date: Tue, 18 Nov 2025 13:04:07 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Wim Van Sebroeck <wim@...ux-watchdog.org>
Cc: linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH] watchdog: Always return time left until watchdog times out

The watchdog core knows when the most recent keepalive was sent. It also
knows the configured timeout. With that, it can always calculate and
return the time left until a watchdog times out, even if its driver does
not support it.

Convert watchdog_get_timeleft() into a void function. It never returns an
error after this patch is applied, so the error checks in the calling code
are now pointless and can be removed.

Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
Tested on system which supports reading the remaining time from the
hardware. Confirmed that the calculated remaining time is never more
than 1 second different than the time reported by the hardware.

 drivers/watchdog/watchdog_dev.c | 35 ++++++++++++++-------------------
 1 file changed, 15 insertions(+), 20 deletions(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 8369fd94fc1a..9a5e544b886b 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -424,20 +424,22 @@ static int watchdog_set_pretimeout(struct watchdog_device *wdd,
  *
  * Get the time before a watchdog will reboot (if not pinged).
  * The caller must hold wd_data->lock.
- *
- * Return: 0 if successful, error otherwise.
  */
-static int watchdog_get_timeleft(struct watchdog_device *wdd,
-							unsigned int *timeleft)
+static void watchdog_get_timeleft(struct watchdog_device *wdd,
+				  unsigned int *timeleft)
 {
 	*timeleft = 0;
 
-	if (!wdd->ops->get_timeleft)
-		return -EOPNOTSUPP;
+	if (wdd->ops->get_timeleft) {
+		*timeleft = wdd->ops->get_timeleft(wdd);
+	} else {
+		struct watchdog_core_data *wd_data = wdd->wd_data;
+		s64 last_keepalive_ms = ktime_ms_delta(ktime_get(), wd_data->last_keepalive);
+		s64 last_keepalive = DIV_ROUND_UP_ULL(last_keepalive_ms, 1000);
 
-	*timeleft = wdd->ops->get_timeleft(wdd);
-
-	return 0;
+		if (wdd->timeout > last_keepalive)
+			*timeleft = wdd->timeout - last_keepalive;
+	}
 }
 
 #ifdef CONFIG_WATCHDOG_SYSFS
@@ -499,16 +501,13 @@ static ssize_t timeleft_show(struct device *dev, struct device_attribute *attr,
 {
 	struct watchdog_device *wdd = dev_get_drvdata(dev);
 	struct watchdog_core_data *wd_data = wdd->wd_data;
-	ssize_t status;
 	unsigned int val;
 
 	mutex_lock(&wd_data->lock);
-	status = watchdog_get_timeleft(wdd, &val);
+	watchdog_get_timeleft(wdd, &val);
 	mutex_unlock(&wd_data->lock);
-	if (!status)
-		status = sysfs_emit(buf, "%u\n", val);
 
-	return status;
+	return sysfs_emit(buf, "%u\n", val);
 }
 static DEVICE_ATTR_RO(timeleft);
 
@@ -624,9 +623,7 @@ static umode_t wdt_is_visible(struct kobject *kobj, struct attribute *attr,
 	struct watchdog_device *wdd = dev_get_drvdata(dev);
 	umode_t mode = attr->mode;
 
-	if (attr == &dev_attr_timeleft.attr && !wdd->ops->get_timeleft)
-		mode = 0;
-	else if (attr == &dev_attr_pretimeout.attr && !watchdog_have_pretimeout(wdd))
+	if (attr == &dev_attr_pretimeout.attr && !watchdog_have_pretimeout(wdd))
 		mode = 0;
 	else if ((attr == &dev_attr_pretimeout_governor.attr ||
 		  attr == &dev_attr_pretimeout_available_governors.attr) &&
@@ -825,9 +822,7 @@ static long watchdog_ioctl(struct file *file, unsigned int cmd,
 		err = put_user(wdd->timeout, p);
 		break;
 	case WDIOC_GETTIMELEFT:
-		err = watchdog_get_timeleft(wdd, &val);
-		if (err < 0)
-			break;
+		watchdog_get_timeleft(wdd, &val);
 		err = put_user(val, p);
 		break;
 	case WDIOC_SETPRETIMEOUT:
-- 
2.45.2