watchdog: imx_sc_wdt: detect if already running

Firmware (SC) WDT can be already enabled in U-Boot. Detect this case and
make CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED functional by setting
WDOG_HW_RUNNING.
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240828060212.108608-1-alexander.sverdlin@siemens.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/imx_sc_wdt.c

@@ -56,6 +56,25 @@ static int imx_sc_wdt_ping(struct watchdog_device *wdog)
 	return 0;
 }
 
+static bool imx_sc_wdt_is_running(void)
+{
+	struct arm_smccc_res res;
+
+	arm_smccc_smc(IMX_SIP_TIMER, IMX_SIP_TIMER_START_WDOG,
+		      0, 0, 0, 0, 0, 0, &res);
+
+	/* Already enabled (SC_TIMER_ERR_BUSY)? */
+	if (res.a0 == SC_TIMER_ERR_BUSY)
+		return true;
+
+	/* Undo only if that was us who has (successfully) enabled the WDT */
+	if (!res.a0)
+		arm_smccc_smc(IMX_SIP_TIMER, IMX_SIP_TIMER_STOP_WDOG,
+			      0, 0, 0, 0, 0, 0, &res);
+
+	return false;
+}
+
 static int imx_sc_wdt_start(struct watchdog_device *wdog)
 {
 	struct arm_smccc_res res;
@@ -183,6 +202,9 @@ static int imx_sc_wdt_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	if (imx_sc_wdt_is_running())
+		set_bit(WDOG_HW_RUNNING, &wdog->status);
+
 	watchdog_stop_on_reboot(wdog);
 	watchdog_stop_on_unregister(wdog);