[rtc-linux] [PATCH] rtc: sunxi: use external oscillator

[Stephan Roslen <stephan@roslen.de>]

We noticed some serious drift problems in Allwinner A20 RTCs. I found out, that the oscillator source needs to be set to an external 32.768 KHz oscillator instead of the internal 32.000 KHz oscillator.

Signed-off-by: Stephan Roslen <stephan@roslen.de>
---
 drivers/rtc/rtc-sunxi.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/rtc/rtc-sunxi.c b/drivers/rtc/rtc-sunxi.c
index abada60..001256e 100644
--- a/drivers/rtc/rtc-sunxi.c
+++ b/drivers/rtc/rtc-sunxi.c
@@ -34,9 +34,19 @@
 #include <linux/types.h>
 
 #define SUNXI_LOSC_CTRL				0x0000
+
+/* magic number required to set bit 0 */
+#define SUNXI_LOSC_CTRL_KEY			0x16AA0000
+
+#define SUNXI_LOSC_CTRL_AUTO_SWT_EN		BIT(14)
+
 #define SUNXI_LOSC_CTRL_RTC_HMS_ACC		BIT(8)
 #define SUNXI_LOSC_CTRL_RTC_YMD_ACC		BIT(7)
 
+#define SUNXI_LOSC_CTRL_EXT_GSM1		BIT(3)
+#define SUNXI_LOSC_CTRL_EXT_GSM0		BIT(2)
+#define SUNXI_LOSC_CTRL_SRC_SEL			BIT(0)
+
 #define SUNXI_RTC_YMD				0x0004
 
 #define SUNXI_RTC_HMS				0x0008
@@ -438,6 +448,8 @@ static int sunxi_rtc_probe(struct platform_device *pdev)
 	struct resource *res;
 	int ret;
 
+	uint32_t loscctrl;
+
 	chip = devm_kzalloc(&pdev->dev, sizeof(*chip), GFP_KERNEL);
 	if (!chip)
 		return -ENOMEM;
@@ -468,6 +480,19 @@ static int sunxi_rtc_probe(struct platform_device *pdev)
 		return -ENODEV;
 	}
 
+	loscctrl = readl(chip->base + SUNXI_LOSC_CTRL);
+	loscctrl &= ~(SUNXI_LOSC_CTRL_AUTO_SWT_EN);
+	loscctrl |= (SUNXI_LOSC_CTRL_SRC_SEL | SUNXI_LOSC_CTRL_KEY);
+	loscctrl |= SUNXI_LOSC_CTRL_EXT_GSM1;
+	writel(loscctrl, chip->base + SUNXI_LOSC_CTRL);
+	udelay(100);
+
+	loscctrl = readl(chip->base + SUNXI_LOSC_CTRL);
+	if (!(loscctrl & SUNXI_LOSC_CTRL_SRC_SEL)) {
+		dev_err(&pdev->dev, "Error: Set LOSC to external failed.\n");
+		dev_err(&pdev->dev, "Warning: RTC time will be wrong!\n");
+	}
+
 	/* clear the alarm count value */
 	writel(0, chip->base + SUNXI_ALRM_DHMS);
 
-- 
2.7.4

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