[PATCH v2] fix it87_wdt early reboot w/ FW started timer

["René Rebe" <rene@exactco.de>]

Some products, such as the Ugreen dxp4800 plus NAS, ship with the it87
wdt enabled by the firmware and a broken BIOS option that does not
allow to change the defautl time or turn it off. This makes installing
Linux difficult and annoyingly rebooting early in an installer; unless
one loads and starts a watchdogd in the installer environment.

Change it87_wdt to report a running timer to the watchdog core using
the user supplied or module's default time and set it as the timer
might already be up and trigger soon.

Signed-off-by: René Rebe <rene@exactco.de>

--- a/drivers/watchdog/it87_wdt.c	2025-09-28 23:39:22.000000000 +0200
+++ b/drivers/watchdog/it87_wdt.c	2025-11-16 14:18:24.759115286 +0100
@@ -4,6 +4,7 @@
  *	   for ITE IT87xx Environment Control - Low Pin Count Input / Output
  *
  *	(c) Copyright 2007  Oliver Schuster <olivers137@aol.com>
+ *	(c) Copyright 2025  René Rebe <rene@exactco.de>
  *
  *	Based on softdog.c	by Alan Cox,
  *		 83977f_wdt.c	by Jose Goncalves,
@@ -188,6 +189,15 @@
 		superio_outb(t >> 8, WDTVALMSB);
 }
 
+/* Internal function, should be called after superio_select(GPIO) */
+static unsigned int _wdt_get_timeout(void)
+{
+	unsigned int ret = superio_inb(WDTVALLSB);
+	if (max_units > 255)
+		ret |= superio_inb(WDTVALMSB) << 8;
+	return ret;
+}
+
 static int wdt_update_timeout(unsigned int t)
 {
 	int ret;
@@ -292,6 +302,7 @@
 	u8 ctrl;
 	int quirks = 0;
 	int rc;
+	unsigned int _timeout;
 
 	rc = superio_enter();
 	if (rc)
@@ -374,8 +385,6 @@
 		}
 	}
 
-	superio_exit();
-
 	if (timeout < 1 || timeout > max_units * 60) {
 		timeout = DEFAULT_TIMEOUT;
 		pr_warn("Timeout value out of range, use default %d sec\n",
@@ -388,6 +397,17 @@
 	wdt_dev.timeout = timeout;
 	wdt_dev.max_timeout = max_units * 60;
 
+	/* wdt already left running by fw bios? */
+	_timeout = _wdt_get_timeout();
+	if (_timeout) {
+		pr_warn("Left running by firmware.\n");
+		wdt_dev.max_hw_heartbeat_ms = timeout * 1000;
+		set_bit(WDOG_HW_RUNNING, &wdt_dev.status);
+		_wdt_update_timeout(timeout);
+	}
+
+	superio_exit();
+
 	watchdog_stop_on_reboot(&wdt_dev);
 	rc = watchdog_register_device(&wdt_dev);
 	if (rc)

-- 
  René Rebe, ExactCODE GmbH, Berlin, Germany
  https://exactcode.com | https://t2linux.com | https://rene.rebe.de