[PATCH] rtc: armada38x: Fix concurrency access in armada38x_rtc_set_time

[Gregory CLEMENT]

While setting the time, the RTC TIME register should not be
accessed. However due to hardware constraints, setting the RTC time
involves sleeping during 100ms. This sleep was done outside the
critical section protected by the spinlock, so it was possible to read
the RTC TIME register and get an incorrect value. This patch
introduces a mutex for protecting the RTC TIME access, unlike the
spinlock it is allowed to sleep in a critical section protected by a
mutex. The RTC STATUS register can still be used from the interrupt
handler but it has no effect on setting the time.

Signed-off-by: Gregory CLEMENT <gregory.clement at free-electrons.com>
Cc: <stable at vger.kernel.org> #v4.0
---
Hi,

I finally got more information about the RTC behavior and while it is
fine accessing RTC_STATUS register during between RTC_STATUS reset and
writing time in RTC_TIME register, reading RTC_TIME during this period
might five incorrect value.

It is too late to fix 4.0, but we are in time for 4.1 and this patch
was tagged to be applied to the stable version of 4.0.

Gregory


 drivers/rtc/rtc-armada38x.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/rtc/rtc-armada38x.c b/drivers/rtc/rtc-armada38x.c
index 43e04af39e09..cb70ced7e0db 100644
--- a/drivers/rtc/rtc-armada38x.c
+++ b/drivers/rtc/rtc-armada38x.c
@@ -40,6 +40,13 @@ struct armada38x_rtc {
 	void __iomem	    *regs;
 	void __iomem	    *regs_soc;
 	spinlock_t	    lock;
+	/*
+	 * While setting the time, the RTC TIME register should not be
+	 * accessed. Setting the RTC time involves sleeping during
+	 * 100ms, so a mutex instead of a spinlock is used to protect
+	 * it
+	 */
+	struct mutex	    mutex_time;
 	int		    irq;
 };
 
@@ -59,8 +66,7 @@ static int armada38x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	struct armada38x_rtc *rtc = dev_get_drvdata(dev);
 	unsigned long time, time_check, flags;
 
-	spin_lock_irqsave(&rtc->lock, flags);
-
+	mutex_lock(&rtc->mutex_time);
 	time = readl(rtc->regs + RTC_TIME);
 	/*
 	 * WA for failing time set attempts. As stated in HW ERRATA if
@@ -71,7 +77,7 @@ static int armada38x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	if ((time_check - time) > 1)
 		time_check = readl(rtc->regs + RTC_TIME);
 
-	spin_unlock_irqrestore(&rtc->lock, flags);
+	mutex_unlock(&rtc->mutex_time);
 
 	rtc_time_to_tm(time_check, tm);
 
@@ -94,19 +100,12 @@ static int armada38x_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	 * then wait for 100ms before writing to the time register to be
 	 * sure that the data will be taken into account.
 	 */
-	spin_lock_irqsave(&rtc->lock, flags);
-
+	mutex_lock(&rtc->mutex_time);
 	rtc_delayed_write(0, rtc, RTC_STATUS);
-
-	spin_unlock_irqrestore(&rtc->lock, flags);
-
 	msleep(100);
-
-	spin_lock_irqsave(&rtc->lock, flags);
-
 	rtc_delayed_write(time, rtc, RTC_TIME);
+	mutex_unlock(&rtc->mutex_time);
 
-	spin_unlock_irqrestore(&rtc->lock, flags);
 out:
 	return ret;
 }
@@ -230,6 +229,7 @@ static __init int armada38x_rtc_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	spin_lock_init(&rtc->lock);
+	mutex_init(&rtc->mutex_time);
 
 	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "rtc");
 	rtc->regs = devm_ioremap_resource(&pdev->dev, res);
-- 
2.1.0