watchdog: arm_smc_wdt: get wdt status through SMCWD_GET_TIMELEFT

The optional SMCWD_GET_TIMELEFT command can be used to detect if
the watchdog has already been started.
See the implementation in OP-TEE secure OS [1].

At probe time, check if the watchdog is already started and then
set WDOG_HW_RUNNING in the watchdog status. This will cause the
watchdog framework to ping the watchdog until a userspace watchdog
daemon takes over the control.

Link: OP-TEE/optee_os@a7f2d4bd8632 [1]

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20250520085952.210723-1-antonio.borneo@foss.st.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Author: AntonioBorneo

drivers/watchdog/arm_smc_wdt.c

@@ -46,6 +46,8 @@ static int smcwd_call(struct watchdog_device *wdd, enum smcwd_call call,
 		return -ENODEV;
 	if (res->a0 == PSCI_RET_INVALID_PARAMS)
 		return -EINVAL;
+	if (res->a0 == PSCI_RET_DISABLED)
+		return -ENODATA;
 	if (res->a0 != PSCI_RET_SUCCESS)
 		return -EIO;
 	return 0;
@@ -131,10 +133,19 @@ static int smcwd_probe(struct platform_device *pdev)
 
 	wdd->info = &smcwd_info;
 	/* get_timeleft is optional */
-	if (smcwd_call(wdd, SMCWD_GET_TIMELEFT, 0, NULL))
-		wdd->ops = &smcwd_ops;
-	else
+	err = smcwd_call(wdd, SMCWD_GET_TIMELEFT, 0, NULL);
+	switch (err) {
+	case 0:
+		set_bit(WDOG_HW_RUNNING, &wdd->status);
+		fallthrough;
+	case -ENODATA:
 		wdd->ops = &smcwd_timeleft_ops;
+		break;
+	default:
+		wdd->ops = &smcwd_ops;
+		break;
+	}
+
 	wdd->timeout = res.a2;
 	wdd->max_timeout = res.a2;
 	wdd->min_timeout = res.a1;