ACPI / watchdog: Prefer iTCO_wdt on Lenovo Z50-70

WDAT table on Lenovo Z50-70 is using RTC SRAM (ports 0x70 and 0x71) to
store state of the timer. This conflicts with Linux RTC driver
(rtc-cmos.c) who fails to reserve those ports for itself preventing RTC
from functioning. In addition the WDAT table seems not to be fully
functional because it does not reset the system when the watchdog times
out.

On this system iTCO_wdt works just fine so we simply prefer to use it
instead of WDAT. This makes RTC working again and also results working
watchdog via iTCO_wdt.
Reported-by: Peter Milley <pbmilley@gmail.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=199033Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_watchdog.c

@@ -12,23 +12,64 @@
 #define pr_fmt(fmt) "ACPI: watchdog: " fmt
 
 #include <linux/acpi.h>
+#include <linux/dmi.h>
 #include <linux/ioport.h>
 #include <linux/platform_device.h>
 
 #include "internal.h"
 
+static const struct dmi_system_id acpi_watchdog_skip[] = {
+	{
+		/*
+		 * On Lenovo Z50-70 there are two issues with the WDAT
+		 * table. First some of the instructions use RTC SRAM
+		 * to store persistent information. This does not work well
+		 * with Linux RTC driver. Second, more important thing is
+		 * that the instructions do not actually reset the system.
+		 *
+		 * On this particular system iTCO_wdt seems to work just
+		 * fine so we prefer that over WDAT for now.
+		 *
+		 * See also https://bugzilla.kernel.org/show_bug.cgi?id=199033.
+		 */
+		.ident = "Lenovo Z50-70",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "20354"),
+			DMI_MATCH(DMI_PRODUCT_VERSION, "Lenovo Z50-70"),
+		},
+	},
+	{}
+};
+
+static const struct acpi_table_wdat *acpi_watchdog_get_wdat(void)
+{
+	const struct acpi_table_wdat *wdat = NULL;
+	acpi_status status;
+
+	if (acpi_disabled)
+		return NULL;
+
+	if (dmi_check_system(acpi_watchdog_skip))
+		return NULL;
+
+	status = acpi_get_table(ACPI_SIG_WDAT, 0,
+				(struct acpi_table_header **)&wdat);
+	if (ACPI_FAILURE(status)) {
+		/* It is fine if there is no WDAT */
+		return NULL;
+	}
+
+	return wdat;
+}
+
 /**
  * Returns true if this system should prefer ACPI based watchdog instead of
  * the native one (which are typically the same hardware).
  */
 bool acpi_has_watchdog(void)
 {
-	struct acpi_table_header hdr;
-
-	if (acpi_disabled)
-		return false;
-
-	return ACPI_SUCCESS(acpi_get_table_header(ACPI_SIG_WDAT, 0, &hdr));
+	return !!acpi_watchdog_get_wdat();
 }
 EXPORT_SYMBOL_GPL(acpi_has_watchdog);
 
@@ -41,12 +82,10 @@ void __init acpi_watchdog_init(void)
 	struct platform_device *pdev;
 	struct resource *resources;
 	size_t nresources = 0;
-	acpi_status status;
 	int i;
 
-	status = acpi_get_table(ACPI_SIG_WDAT, 0,
-				(struct acpi_table_header **)&wdat);
-	if (ACPI_FAILURE(status)) {
+	wdat = acpi_watchdog_get_wdat();
+	if (!wdat) {
 		/* It is fine if there is no WDAT */
 		return;
 	}