watchdog: rti_wdt: Fix calculation and evaluation of preset heartbeat

This ensures that the same value is read back as was eventually
programmed when using seconds as accuracy. Even then, comparing the more
precise heartbeat_ms against heartbeat in seconds will almost never
provide a match and will needlessly raise a warning. Fix by comparing
apples to apples.

Tested in combination with U-Boot as watchdog starter.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/6a4b54ac-9588-e172-c4c7-b91d524a851e@siemens.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/rti_wdt.c

@@ -253,6 +253,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
 	}
 
 	if (readl(wdt->base + RTIDWDCTRL) == WDENABLE_KEY) {
+		int preset_heartbeat;
 		u32 time_left_ms;
 		u64 heartbeat_ms;
 		u32 wsize;
@@ -263,11 +264,12 @@ static int rti_wdt_probe(struct platform_device *pdev)
 		heartbeat_ms <<= WDT_PRELOAD_SHIFT;
 		heartbeat_ms *= 1000;
 		do_div(heartbeat_ms, wdt->freq);
-		if (heartbeat_ms != heartbeat * 1000)
+		preset_heartbeat = heartbeat_ms + 500;
+		preset_heartbeat /= 1000;
+		if (preset_heartbeat != heartbeat)
 			dev_warn(dev, "watchdog already running, ignoring heartbeat config!\n");
 
-		heartbeat = heartbeat_ms;
-		heartbeat /= 1000;
+		heartbeat = preset_heartbeat;
 
 		wsize = readl(wdt->base + RTIWWDSIZECTRL);
 		ret = rti_wdt_setup_hw_hb(wdd, wsize);