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: https://github.com/OP-TEE/optee_os/commit/a7f2d4bd8632 [1]

Signed-off-by: Antonio Borneo <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

drivers/watchdog/arm_smc_wdt.c

···
 		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;
···
 
 	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;