[PATCH V2] rtc: zynqmp: Add calibration set and get support

[Srinivas Neeli]

Zynqmp RTC controller has a calibration feature to compensate
time deviation due to input clock inaccuracy.
Set and get calibration API's are used for setting and getting
calibration value from the controller calibration register.

Signed-off-by: Srinivas Neeli <srinivas.neeli@xxxxxxxxxx>
---
Changes in V2:
-Removed unused macro.
-Updated code with review comments.
---
 drivers/rtc/rtc-zynqmp.c | 100 ++++++++++++++++++++++++++++++++-------
 1 file changed, 83 insertions(+), 17 deletions(-)

diff --git a/drivers/rtc/rtc-zynqmp.c b/drivers/rtc/rtc-zynqmp.c
index f440bb52be92..3731ddfbd90f 100644
--- a/drivers/rtc/rtc-zynqmp.c
+++ b/drivers/rtc/rtc-zynqmp.c
@@ -36,10 +36,15 @@
 #define RTC_OSC_EN		BIT(24)
 #define RTC_BATT_EN		BIT(31)
 
-#define RTC_CALIB_DEF		0x198233
+#define RTC_CALIB_DEF		0x8000
 #define RTC_CALIB_MASK		0x1FFFFF
 #define RTC_ALRM_MASK          BIT(1)
 #define RTC_MSEC               1000
+#define RTC_FR_MASK		0xF0000
+#define RTC_FR_MAX_TICKS	16
+#define RTC_OFFSET_MAX		150000
+#define RTC_OFFSET_MIN		-150000
+#define RTC_PPB			1000000000LL
 
 struct xlnx_rtc_dev {
 	struct rtc_device	*rtc;
@@ -61,13 +66,6 @@ static int xlnx_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	 */
 	new_time = rtc_tm_to_time64(tm) + 1;
 
-	/*
-	 * Writing into calibration register will clear the Tick Counter and
-	 * force the next second to be signaled exactly in 1 second period
-	 */
-	xrtcdev->calibval &= RTC_CALIB_MASK;
-	writel(xrtcdev->calibval, (xrtcdev->reg_base + RTC_CALIB_WR));
-
 	writel(new_time, xrtcdev->reg_base + RTC_SET_TM_WR);
 
 	/*
@@ -174,14 +172,76 @@ static void xlnx_init_rtc(struct xlnx_rtc_dev *xrtcdev)
 	rtc_ctrl |= RTC_BATT_EN;
 	writel(rtc_ctrl, xrtcdev->reg_base + RTC_CTRL);
 
-	/*
-	 * Based on crystal freq of 33.330 KHz
-	 * set the seconds counter and enable, set fractions counter
-	 * to default value suggested as per design spec
-	 * to correct RTC delay in frequency over period of time.
+	/* Update calibvalue */
+	xrtcdev->calibval = readl(xrtcdev->reg_base + RTC_CALIB_RD);
+}
+
+static int xlnx_rtc_read_offset(struct device *dev, long *offset)
+{
+	struct xlnx_rtc_dev *xrtcdev = dev_get_drvdata(dev);
+	long offset_val = 0;
+	unsigned int tick_mult = RTC_PPB / (xrtcdev->calibval & RTC_TICK_MASK);
+
+	/* Offset with seconds ticks */
+	offset_val = xrtcdev->calibval & RTC_TICK_MASK;
+	offset_val = offset_val - RTC_CALIB_DEF;
+	offset_val = offset_val * tick_mult;
+
+	/* Offset with fractional ticks */
+	if (xrtcdev->calibval & RTC_FR_EN)
+		offset_val += ((xrtcdev->calibval & RTC_FR_MASK) >> RTC_FR_DATSHIFT)
+			* (tick_mult / RTC_FR_MAX_TICKS);
+	*offset = offset_val;
+
+	return 0;
+}
+
+static int xlnx_rtc_set_offset(struct device *dev, long offset)
+{
+	struct xlnx_rtc_dev *xrtcdev = dev_get_drvdata(dev);
+	short int  max_tick;
+	unsigned char fract_tick = 0;
+	unsigned int calibval;
+	int fract_offset;
+	unsigned int tick_mult = RTC_PPB / (xrtcdev->calibval & RTC_TICK_MASK);
+
+	/* Make sure offset value is within supported range */
+	if (offset < RTC_OFFSET_MIN || offset > RTC_OFFSET_MAX)
+		return -ERANGE;
+
+	/* Number ticks for given offset */
+	max_tick = div_s64_rem(offset, tick_mult, &fract_offset);
+
+	/* Number fractional ticks for given offset */
+	if (fract_offset) {
+		if (fract_offset < 0) {
+			fract_offset = fract_offset + tick_mult;
+			max_tick--;
+		}
+		if (fract_offset > (tick_mult / RTC_FR_MAX_TICKS)) {
+			for (fract_tick = 1; fract_tick < 16; fract_tick++) {
+				if (fract_offset <=
+				    (fract_tick *
+				     (tick_mult / RTC_FR_MAX_TICKS)))
+					break;
+			}
+		}
+	}
+
+	/* Zynqmp RTC uses second and fractional tick
+	 * counters for compensation
 	 */
-	xrtcdev->calibval &= RTC_CALIB_MASK;
-	writel(xrtcdev->calibval, (xrtcdev->reg_base + RTC_CALIB_WR));
+	calibval = max_tick + RTC_CALIB_DEF;
+
+	if (fract_tick)
+		calibval |= RTC_FR_EN;
+
+	calibval |= (fract_tick << RTC_FR_DATSHIFT);
+
+	writel(calibval, (xrtcdev->reg_base + RTC_CALIB_WR));
+	xrtcdev->calibval = calibval;
+
+	return 0;
 }
 
 static const struct rtc_class_ops xlnx_rtc_ops = {
@@ -190,6 +250,8 @@ static const struct rtc_class_ops xlnx_rtc_ops = {
 	.read_alarm	  = xlnx_rtc_read_alarm,
 	.set_alarm	  = xlnx_rtc_set_alarm,
 	.alarm_irq_enable = xlnx_rtc_alarm_irq_enable,
+	.read_offset	  = xlnx_rtc_read_offset,
+	.set_offset	  = xlnx_rtc_set_offset,
 };
 
 static irqreturn_t xlnx_rtc_interrupt(int irq, void *id)
@@ -215,6 +277,7 @@ static int xlnx_rtc_probe(struct platform_device *pdev)
 {
 	struct xlnx_rtc_dev *xrtcdev;
 	int ret;
+	unsigned int calibval;
 
 	xrtcdev = devm_kzalloc(&pdev->dev, sizeof(*xrtcdev), GFP_KERNEL);
 	if (!xrtcdev)
@@ -256,9 +319,12 @@ static int xlnx_rtc_probe(struct platform_device *pdev)
 	}
 
 	ret = of_property_read_u32(pdev->dev.of_node, "calibration",
-				   &xrtcdev->calibval);
+				   &calibval);
 	if (ret)
-		xrtcdev->calibval = RTC_CALIB_DEF;
+		calibval = RTC_CALIB_DEF;
+	ret = readl(xrtcdev->reg_base + RTC_CALIB_RD);
+	if (!ret)
+		writel(calibval, (xrtcdev->reg_base + RTC_CALIB_WR));
 
 	xlnx_init_rtc(xrtcdev);
 
-- 
2.17.1