ACPI / watchdog: Prefer iTCO_wdt always when WDAT table uses RTC SRAM

After we added quirk for Lenovo Z50-70 it turns out there are at least
two more systems where WDAT table includes instructions accessing RTC
SRAM. Instead of quirking each system separately, look for such
instructions in the table and automatically prefer iTCO_wdt if found.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=199033
Reported-by: Arnold Guy <aurnoldg@gmail.com>
Reported-by: Alois Nespor <nespor@fssp.cz>
Reported-by: Yury Pakin <zxwarior@gmail.com>
Reported-by: Ihor Chyhin <ihorchyhin@ukr.net>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_watchdog.c

@@ -12,35 +12,51 @@
 #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"),
-		},
-	},
-	{}
-};
+#ifdef CONFIG_RTC_MC146818_LIB
+#include <linux/mc146818rtc.h>
+
+/*
+ * There are several systems where the WDAT table is accessing RTC SRAM to
+ * store persistent information. This does not work well with the Linux RTC
+ * driver so on those systems we skip WDAT driver and prefer iTCO_wdt
+ * instead.
+ *
+ * See also https://bugzilla.kernel.org/show_bug.cgi?id=199033.
+ */
+static bool acpi_watchdog_uses_rtc(const struct acpi_table_wdat *wdat)
+{
+	const struct acpi_wdat_entry *entries;
+	int i;
+
+	entries = (struct acpi_wdat_entry *)(wdat + 1);
+	for (i = 0; i < wdat->entries; i++) {
+		const struct acpi_generic_address *gas;
+
+		gas = &entries[i].register_region;
+		if (gas->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
+			switch (gas->address) {
+			case RTC_PORT(0):
+			case RTC_PORT(1):
+			case RTC_PORT(2):
+			case RTC_PORT(3):
+				return true;
+			}
+		}
+	}
+
+	return false;
+}
+#else
+static bool acpi_watchdog_uses_rtc(const struct acpi_table_wdat *wdat)
+{
+	return false;
+}
+#endif
 
 static const struct acpi_table_wdat *acpi_watchdog_get_wdat(void)
 {
@@ -50,16 +66,18 @@ static const struct acpi_table_wdat *acpi_watchdog_get_wdat(void)
 	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;
 	}
 
+	if (acpi_watchdog_uses_rtc(wdat)) {
+		pr_info("Skipping WDAT on this system because it uses RTC SRAM\n");
+		return NULL;
+	}
+
 	return wdat;
 }