ACPI: watchdog: Allow disabling WDAT at boot

In case the WDAT interface is broken, give the user an option to
ignore it to let a native driver bind to the watchdog device instead.
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -136,6 +136,10 @@
 			dynamic table installation which will install SSDT
 			tables to /sys/firmware/acpi/tables/dynamic.
 
+	acpi_no_watchdog	[HW,ACPI,WDT]
+			Ignore the ACPI-based watchdog interface (WDAT) and let
+			a native driver control the watchdog device instead.
+
 	acpi_rsdp=	[ACPI,EFI,KEXEC]
 			Pass the RSDP address to the kernel, mostly used
 			on machines running EFI runtime service to boot the

drivers/acpi/acpi_watchdog.c

@@ -55,12 +55,14 @@ static bool acpi_watchdog_uses_rtc(const struct acpi_table_wdat *wdat)
 }
 #endif
 
+static bool acpi_no_watchdog;
+
 static const struct acpi_table_wdat *acpi_watchdog_get_wdat(void)
 {
 	const struct acpi_table_wdat *wdat = NULL;
 	acpi_status status;
 
-	if (acpi_disabled)
+	if (acpi_disabled || acpi_no_watchdog)
 		return NULL;
 
 	status = acpi_get_table(ACPI_SIG_WDAT, 0,
@@ -88,6 +90,14 @@ bool acpi_has_watchdog(void)
 }
 EXPORT_SYMBOL_GPL(acpi_has_watchdog);
 
+/* ACPI watchdog can be disabled on boot command line */
+static int __init disable_acpi_watchdog(char *str)
+{
+	acpi_no_watchdog = true;
+	return 1;
+}
+__setup("acpi_no_watchdog", disable_acpi_watchdog);
+
 void __init acpi_watchdog_init(void)
 {
 	const struct acpi_wdat_entry *entries;