[PATCH v1 1/1] rtc: zynqmp: ensure correct RTC calibration

[Lothar Rubusch]

From: Ivan Vera <ivan.vera at enclustra.com>

In the event of an uninitialized calibration register, ensure the register
is reset and properly programmed during the probe sequence.

At present, only the calibration register is evaluated. If it holds invalid
values after a power cycle, there's no longer a way to reset it, for
instance, via a devicetree entry to 0x7FFF. This issue is documented here:
https://adaptivesupport.amd.com/s/article/000036886?language=en_US 

The fix prioritizes an optional calibration value provided via the
devicetree over the value in the register.

Fixes: 07dcc6f9c76275d6679f28a69e042a2f9dc8f128 ("rtc: zynqmp: Add calibration set and get support")
Signed-off-by: Ivan Vera <ivan.vera at enclustra.com>
Signed-off-by: Lothar Rubusch <l.rubusch at gmail.com>
---
 drivers/rtc/rtc-zynqmp.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/rtc/rtc-zynqmp.c b/drivers/rtc/rtc-zynqmp.c
index f39102b66eac..0c063c3fae52 100644
--- a/drivers/rtc/rtc-zynqmp.c
+++ b/drivers/rtc/rtc-zynqmp.c
@@ -331,9 +331,9 @@ static int xlnx_rtc_probe(struct platform_device *pdev)
 		if (ret)
 			xrtcdev->freq = RTC_CALIB_DEF;
 	}
-	ret = readl(xrtcdev->reg_base + RTC_CALIB_RD);
-	if (!ret)
-		writel(xrtcdev->freq, (xrtcdev->reg_base + RTC_CALIB_WR));
+
+	/* Enable unconditional re-calibration to RTC_CALIB_DEF or DTB entry. */
+	writel(xrtcdev->freq, xrtcdev->reg_base + RTC_CALIB_WR);
 
 	xlnx_init_rtc(xrtcdev);
 
-- 
2.39.5