diff --git a/drivers/rtc/rtc-at91rm9200.c b/drivers/rtc/rtc-at91rm9200.c
index 0eab77b..5f722c0 100644
--- a/drivers/rtc/rtc-at91rm9200.c
+++ b/drivers/rtc/rtc-at91rm9200.c
@@ -27,6 +27,7 @@
 #include <linux/interrupt.h>
 #include <linux/ioctl.h>
 #include <linux/completion.h>
+#include <linux/spinlock.h>
 #include <linux/io.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
@@ -43,10 +44,67 @@
 #define AT91_RTC_EPOCH		1900UL	/* just like arch/arm/common/rtctime.c */
 
 static DECLARE_COMPLETION(at91_rtc_updated);
+
+static DEFINE_SPINLOCK(at91_rtc_broken_imr);
+
 static unsigned int at91_alarm_year = AT91_RTC_EPOCH;
 static void __iomem *at91_rtc_regs;
 static int irq;
 
+static bool has_broken_imr;
+static int shadow_rtc_imr;
+
+
+
+static u32 at91_rtc_read_imr(void)
+{
+	if (has_broken_imr)
+		return shadow_rtc_imr;
+	else
+		return at91_rtc_read(AT91_RTC_IMR);
+}
+
+static void at91_rtc_write_ier(u32 val)
+{
+	if (has_broken_imr) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&at91_rtc_broken_imr, flags);
+		shadow_rtc_imr |= val;
+		at91_rtc_write(AT91_RTC_IER, val);
+		spin_unlock_irqrestore(&at91_rtc_broken_imr, flags);
+	} else
+		at91_rtc_write(AT91_RTC_IER, val);
+}
+
+static void at91_rtc_write_idr(u32 val)
+{
+	if (has_broken_imr) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&at91_rtc_broken_imr, flags);
+		shadow_rtc_imr &= ~val;
+		at91_rtc_write(AT91_RTC_IDR, val);
+		spin_unlock_irqrestore(&at91_rtc_broken_imr, flags);
+	} else
+		at91_rtc_write(AT91_RTC_IDR, val);
+}
+
+/*
+ * Check if AT91_RTC_IMR correctly reports AT91_RTC_CALEV enabled. Then
+ * disable all known rtc interrupts.
+ */
+static void at91_rtc_check_imr_and_disable(void)
+{
+	at91_rtc_write(AT91_RTC_IER, AT91_RTC_ACKUPD);
+	has_broken_imr = ! (AT91_RTC_ACKUPD & at91_rtc_read(AT91_RTC_IMR));
+	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ACKUPD | AT91_RTC_ALARM |
+				     AT91_RTC_SECEV | AT91_RTC_TIMEV |
+				     AT91_RTC_CALEV);
+	if (has_broken_imr)
+		shadow_rtc_imr = 0;
+}
+
 /*
  * Decode time/date into rtc_time structure
  */
@@ -110,9 +168,9 @@ static int at91_rtc_settime(struct device *dev, struct rtc_time *tm)
 	cr = at91_rtc_read(AT91_RTC_CR);
 	at91_rtc_write(AT91_RTC_CR, cr | AT91_RTC_UPDCAL | AT91_RTC_UPDTIM);
 
-	at91_rtc_write(AT91_RTC_IER, AT91_RTC_ACKUPD);
+	at91_rtc_write_ier(AT91_RTC_ACKUPD);
 	wait_for_completion(&at91_rtc_updated);	/* wait for ACKUPD interrupt */
-	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ACKUPD);
+	at91_rtc_write_idr(AT91_RTC_ACKUPD);
 
 	at91_rtc_write(AT91_RTC_TIMR,
 			  bin2bcd(tm->tm_sec) << 0
@@ -169,7 +227,7 @@ static int at91_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
 	tm.tm_min = alrm->time.tm_min;
 	tm.tm_sec = alrm->time.tm_sec;
 
-	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ALARM);
+	at91_rtc_write_idr(AT91_RTC_ALARM);
 	at91_rtc_write(AT91_RTC_TIMALR,
 		  bin2bcd(tm.tm_sec) << 0
 		| bin2bcd(tm.tm_min) << 8
@@ -182,7 +240,7 @@ static int at91_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
 
 	if (alrm->enabled) {
 		at91_rtc_write(AT91_RTC_SCCR, AT91_RTC_ALARM);
-		at91_rtc_write(AT91_RTC_IER, AT91_RTC_ALARM);
+		at91_rtc_write_ier(AT91_RTC_ALARM);
 	}
 
 	dev_dbg(dev, "%s(): %4d-%02d-%02d %02d:%02d:%02d\n", __func__,
@@ -198,9 +256,9 @@ static int at91_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
 
 	if (enabled) {
 		at91_rtc_write(AT91_RTC_SCCR, AT91_RTC_ALARM);
-		at91_rtc_write(AT91_RTC_IER, AT91_RTC_ALARM);
+		at91_rtc_write_ier(AT91_RTC_ALARM);
 	} else
-		at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ALARM);
+		at91_rtc_write_idr(AT91_RTC_ALARM);
 
 	return 0;
 }
@@ -229,7 +287,7 @@ static irqreturn_t at91_rtc_interrupt(int irq, void *dev_id)
 	unsigned int rtsr;
 	unsigned long events = 0;
 
-	rtsr = at91_rtc_read(AT91_RTC_SR) & at91_rtc_read(AT91_RTC_IMR);
+	rtsr = at91_rtc_read(AT91_RTC_SR) & at91_rtc_read_imr();
 	if (rtsr) {		/* this interrupt is shared!  Is it ours? */
 		if (rtsr & AT91_RTC_ALARM)
 			events |= (RTC_AF | RTC_IRQF);
@@ -289,10 +347,9 @@ static int __init at91_rtc_probe(struct platform_device *pdev)
 	at91_rtc_write(AT91_RTC_CR, 0);
 	at91_rtc_write(AT91_RTC_MR, 0);		/* 24 hour mode */
 
+	/* AT91_RTC_IMR register is broken on some SoCs using this driver */
 	/* Disable all interrupts */
-	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ACKUPD | AT91_RTC_ALARM |
-					AT91_RTC_SECEV | AT91_RTC_TIMEV |
-					AT91_RTC_CALEV);
+	at91_rtc_check_imr_and_disable();
 
 	ret = request_irq(irq, at91_rtc_interrupt,
 				IRQF_SHARED,
@@ -316,7 +373,8 @@ static int __init at91_rtc_probe(struct platform_device *pdev)
 	}
 	platform_set_drvdata(pdev, rtc);
 
-	dev_info(&pdev->dev, "AT91 Real Time Clock driver.\n");
+	dev_info(&pdev->dev, "AT91 Real Time Clock driver.%s\n",
+		 (has_broken_imr ? " [AT91_RTC_IMR broken]" : ""));
 	return 0;
 
 err_free_irq:
@@ -335,9 +393,9 @@ static int __exit at91_rtc_remove(struct platform_device *pdev)
 	struct rtc_device *rtc = platform_get_drvdata(pdev);
 
 	/* Disable all interrupts */
-	at91_rtc_write(AT91_RTC_IDR, AT91_RTC_ACKUPD | AT91_RTC_ALARM |
-					AT91_RTC_SECEV | AT91_RTC_TIMEV |
-					AT91_RTC_CALEV);
+	at91_rtc_write_idr(AT91_RTC_ACKUPD | AT91_RTC_ALARM |
+			   AT91_RTC_SECEV | AT91_RTC_TIMEV |
+			   AT91_RTC_CALEV);
 	free_irq(irq, pdev);
 
 	rtc_device_unregister(rtc);
@@ -364,7 +422,7 @@ static int at91_rtc_suspend(struct device *dev)
 		if (device_may_wakeup(dev))
 			enable_irq_wake(irq);
 		else
-			at91_rtc_write(AT91_RTC_IDR, at91_rtc_imr);
+			at91_rtc_write_idr(at91_rtc_imr);
 	}
 	return 0;
 }
@@ -375,7 +433,7 @@ static int at91_rtc_resume(struct device *dev)
 		if (device_may_wakeup(dev))
 			disable_irq_wake(irq);
 		else
-			at91_rtc_write(AT91_RTC_IER, at91_rtc_imr);
+			at91_rtc_write_ier(at91_rtc_imr);
 	}
 	return 0;
 }
-- 
1.7.10.4


