rtc: armada38x: Align RTC set time procedure with the official errata

According to the Armada38x functional errata FE-3124064, writing to
the RTC TIME register may fail. As a workaround, after writing to RTC
TIME register, issue a dummy write of 0x0 twice to the RTC Status
register.  This is the updated implementation of the Errata that
eliminates the need of the long 100ms delay during the RTC set time
procedure.

[gregory.clement@free-electrons.com]: removed the mutex and use the
spinlock again

Signed-off-by: Nadav Haklai <nadavh@marvell.com>
Reviewed-by: Neta Zur Hershkovits <neta@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-armada38x.c

@@ -40,13 +40,6 @@ 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;
 };
 
@@ -64,9 +57,9 @@ static void rtc_delayed_write(u32 val, struct armada38x_rtc *rtc, int offset)
 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;
+	unsigned long time, time_check, flags;
 
-	mutex_lock(&rtc->mutex_time);
+	spin_lock_irqsave(&rtc->lock, flags);
 	time = readl(rtc->regs + RTC_TIME);
 	/*
 	 * WA for failing time set attempts. As stated in HW ERRATA if
@@ -77,7 +70,7 @@ 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);
 
-	mutex_unlock(&rtc->mutex_time);
+	spin_unlock_irqrestore(&rtc->lock, flags);
 
 	rtc_time_to_tm(time_check, tm);
 
@@ -88,23 +81,23 @@ static int armada38x_rtc_set_time(struct device *dev, struct rtc_time *tm)
 {
 	struct armada38x_rtc *rtc = dev_get_drvdata(dev);
 	int ret = 0;
-	unsigned long time;
+	unsigned long time, flags;
 
 	ret = rtc_tm_to_time(tm, &time);
 
 	if (ret)
 		goto out;
 	/*
-	 * Setting the RTC time not always succeeds. According to the
-	 * errata we need to first write on the status register and
-	 * then wait for 100ms before writing to the time register to be
-	 * sure that the data will be taken into account.
+	 * According to errata FE-3124064, Write to RTC TIME register
+	 * may fail. As a workaround, after writing to RTC TIME
+	 * register, issue a dummy write of 0x0 twice to RTC Status
+	 * register.
 	 */
-	mutex_lock(&rtc->mutex_time);
-	rtc_delayed_write(0, rtc, RTC_STATUS);
-	msleep(100);
+	spin_lock_irqsave(&rtc->lock, flags);
 	rtc_delayed_write(time, rtc, RTC_TIME);
-	mutex_unlock(&rtc->mutex_time);
+	rtc_delayed_write(0, rtc, RTC_STATUS);
+	rtc_delayed_write(0, rtc, RTC_STATUS);
+	spin_unlock_irqrestore(&rtc->lock, flags);
 
 out:
 	return ret;
@@ -229,7 +222,6 @@ 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);