[ARM] Kirkwood: fail the probe if internal RTC does not work

Having a RTC that doesn't maintain proper time across a reboot is one
thing.  But a RTC that doesn't work at all and only causes timeouts is
another.
Tested-by: Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>

drivers/rtc/rtc-mv.c

@@ -12,6 +12,7 @@
 #include <linux/bcd.h>
 #include <linux/io.h>
 #include <linux/platform_device.h>
+#include <linux/delay.h>
 
 
 #define RTC_TIME_REG_OFFS	0
@@ -119,6 +120,16 @@ static int __init mv_rtc_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
+	/* make sure it is actually functional */
+	if (rtc_time == 0x01000000) {
+		ssleep(1);
+		rtc_time = readl(pdata->ioaddr + RTC_TIME_REG_OFFS);
+		if (rtc_time == 0x01000000) {
+			dev_err(&pdev->dev, "internal RTC not ticking\n");
+			return -ENODEV;
+		}
+	}
+
 	platform_set_drvdata(pdev, pdata);
 	pdata->rtc = rtc_device_register(pdev->name, &pdev->dev,
 					 &mv_rtc_ops, THIS_MODULE);