rtc: zynqmp: Update seconds time programming logic

We program RTC time using SET_TIME_WRITE register and read the RTC
current time using CURRENT_TIME register. When we set the time by
writing into SET_TIME_WRITE Register and immediately try to read the
rtc time from CURRENT_TIME register, the previous old value is
returned instead of the new loaded time. This is because RTC takes
nearly 1 sec to update the  new loaded value into the CURRENT_TIME
register. This behaviour is expected in our RTC IP.

This patch updates the driver to read the current time from SET_TIME_WRITE
register instead of CURRENT_TIME when rtc time is requested within an 1sec
period after setting the RTC time. Doing so will ensure the correct time is
given to the user.

Since there is a delay of 1sec in updating the CURRENT_TIME we are loading
set time +1sec while programming the SET_TIME_WRITE register, doing this
will give correct time without any delay when read from CURRENT_TIME.
Signed-off-by: Anurag Kumar Vulisha <anuragku@xilinx.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-zynqmp.c

@@ -64,7 +64,12 @@ static int xlnx_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	struct xlnx_rtc_dev *xrtcdev = dev_get_drvdata(dev);
 	unsigned long new_time;
 
-	new_time = rtc_tm_to_time64(tm);
+	/*
+	 * The value written will be updated after 1 sec into the
+	 * seconds read register, so we need to program time +1 sec
+	 * to get the correct time on read.
+	 */
+	new_time = rtc_tm_to_time64(tm) + 1;
 
 	if (new_time > RTC_SEC_MAX_VAL)
 		return -EINVAL;
@@ -78,14 +83,44 @@ static int xlnx_rtc_set_time(struct device *dev, struct rtc_time *tm)
 
 	writel(new_time, xrtcdev->reg_base + RTC_SET_TM_WR);
 
+	/*
+	 * Clear the rtc interrupt status register after setting the
+	 * time. During a read_time function, the code should read the
+	 * RTC_INT_STATUS register and if bit 0 is still 0, it means
+	 * that one second has not elapsed yet since RTC was set and
+	 * the current time should be read from SET_TIME_READ register;
+	 * otherwise, CURRENT_TIME register is read to report the time
+	 */
+	writel(RTC_INT_SEC, xrtcdev->reg_base + RTC_INT_STS);
+
 	return 0;
 }
 
 static int xlnx_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
+	u32 status;
+	unsigned long read_time;
 	struct xlnx_rtc_dev *xrtcdev = dev_get_drvdata(dev);
 
-	rtc_time64_to_tm(readl(xrtcdev->reg_base + RTC_CUR_TM), tm);
+	status = readl(xrtcdev->reg_base + RTC_INT_STS);
+
+	if (status & RTC_INT_SEC) {
+		/*
+		 * RTC has updated the CURRENT_TIME with the time written into
+		 * SET_TIME_WRITE register.
+		 */
+		rtc_time64_to_tm(readl(xrtcdev->reg_base + RTC_CUR_TM), tm);
+	} else {
+		/*
+		 * Time written in SET_TIME_WRITE has not yet updated into
+		 * the seconds read register, so read the time from the
+		 * SET_TIME_WRITE instead of CURRENT_TIME register.
+		 * Since we add +1 sec while writing, we need to -1 sec while
+		 * reading.
+		 */
+		read_time = readl(xrtcdev->reg_base + RTC_SET_TM_RD) - 1;
+		rtc_time64_to_tm(read_time, tm);
+	}
 
 	return rtc_valid_tm(tm);
 }
@@ -166,11 +201,9 @@ static irqreturn_t xlnx_rtc_interrupt(int irq, void *id)
 	if (!(status & (RTC_INT_SEC | RTC_INT_ALRM)))
 		return IRQ_NONE;
 
-	/* Clear interrupt */
-	writel(status, xrtcdev->reg_base + RTC_INT_STS);
+	/* Clear RTC_INT_ALRM interrupt only */
+	writel(RTC_INT_ALRM, xrtcdev->reg_base + RTC_INT_STS);
 
-	if (status & RTC_INT_SEC)
-		rtc_update_irq(xrtcdev->rtc, 1, RTC_IRQF | RTC_UF);
 	if (status & RTC_INT_ALRM)
 		rtc_update_irq(xrtcdev->rtc, 1, RTC_IRQF | RTC_AF);