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 <[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/imx_sc_wdt.c

···
 	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;
···
 	ret = imx_sc_wdt_set_timeout(wdog, wdog->timeout);
 	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);