watchdog: wdat_wdt: Avoid unimplemented get_timeleft

As per the specification the action QUERY_COUNTDOWN_PERIOD is optional.
If the action is not implemented by the physical device the driver would
always report "0" from get_timeleft().
Avoid confusing userspace by only providing get_timeleft() when
implemented by the hardware.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20221221-wdat_wdt-timeleft-v1-1-8e8a314c36cc@weissschuh.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/wdat_wdt.c

@@ -301,13 +301,12 @@ static const struct watchdog_info wdat_wdt_info = {
 	.identity = "wdat_wdt",
 };
 
-static const struct watchdog_ops wdat_wdt_ops = {
+static struct watchdog_ops wdat_wdt_ops = {
 	.owner = THIS_MODULE,
 	.start = wdat_wdt_start,
 	.stop = wdat_wdt_stop,
 	.ping = wdat_wdt_ping,
 	.set_timeout = wdat_wdt_set_timeout,
-	.get_timeleft = wdat_wdt_get_timeleft,
 };
 
 static int wdat_wdt_probe(struct platform_device *pdev)
@@ -436,6 +435,9 @@ static int wdat_wdt_probe(struct platform_device *pdev)
 		list_add_tail(&instr->node, instructions);
 	}
 
+	if (wdat->instructions[ACPI_WDAT_GET_CURRENT_COUNTDOWN])
+		wdat_wdt_ops.get_timeleft = wdat_wdt_get_timeleft;
+
 	wdat_wdt_boot_status(wdat);
 	wdat_wdt_set_running(wdat);