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Banana pi clock drift patch

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https://github.com/armbian/build/issues/834
This commit is contained in:
Igor Pecovnik 2017-12-13 12:30:41 +01:00
parent 67984f1078
commit 2fb1217966
1 changed files with 121 additions and 0 deletions
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121
patch/kernel/sunxi-next/rtc-sunxi-clocksource.patch Normal file
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@ -0,0 +1,121 @@
This adds a sysfs 'clock_source' attribute which can be used to query
and set the clock source of the RTC, either 'internal' or 'external'.
Important note: Probing the pins of the 32kHz crystal with a scope will
not reliably tell you whether the (usually) more accurate external is
selected! On a 'Cubietech Cubietruck' board, the author saw a stable
32768Hz signal on the crystal, even though the internal oscillator was
selected and the clock wildly drifting.
Using adjtimex might help to figure out which oscillator is selected:
~# echo internal > /sys/devices/.../1c20d00.rtc/clock_source
~# adjtimex -n -c=3
--- current --- -- suggested --
cmos time system-cmos error_ppm tick freq tick freq
1469627826 31.224561
1469627835 31.858098 63353.6 10000 0
1469627844 32.490782 63268.4 10000 0 9367 2069425
~# echo external > /sys/devices/.../1c20d00.rtc/clock_source
~# adjtimex -n -c=3
--- current --- -- suggested --
cmos time system-cmos error_ppm tick freq tick freq
1469627851 32.883407
1469627861 32.883380 -2.7 10000 0
1469627871 32.883352 -2.8 10000 0 10000 185937
Signed-off-by: Onno Kortmann <on...@gmx.net>
---
drivers/rtc/rtc-sunxi.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 54 insertions(+)
diff --git a/drivers/rtc/rtc-sunxi.c b/drivers/rtc/rtc-sunxi.c
index abada60..3fcf571 100644
--- a/drivers/rtc/rtc-sunxi.c
+++ b/drivers/rtc/rtc-sunxi.c
@@ -36,6 +36,8 @@
#define SUNXI_LOSC_CTRL 0x0000
#define SUNXI_LOSC_CTRL_RTC_HMS_ACC BIT(8)
#define SUNXI_LOSC_CTRL_RTC_YMD_ACC BIT(7)
+#define SUNXI_LOSC_OSC32K_SRC_SEL BIT(0)
+#define SUNXI_LOSC_KEY_VALUE 0x16aa0000
#define SUNXI_RTC_YMD 0x0004
@@ -432,6 +434,50 @@ static const struct of_device_id sunxi_rtc_dt_ids[] = {
};
MODULE_DEVICE_TABLE(of, sunxi_rtc_dt_ids);
+/* As per page 126 of the A20 manual, the lowest bit in LOSC_CTRL_REG controls
+ * the 32.768KHz clock source to use for the RTC. Using the clock_source sysfs
+ * attribute, the clock can be selected between external (accurate 32kHz
+ * crystal) and internal (seems to be an inaccurate RC oscillator) mode. It
+ * appears that this bit is non-volatile and will be kept in the RTC when the
+ * system is powered off.
+ */
+static ssize_t sunxi_rtc_show_clock_source(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct sunxi_rtc_dev *chip = dev_get_drvdata(dev);
+ u32 val = readl(chip->base + SUNXI_LOSC_CTRL);
+ if (val & SUNXI_LOSC_OSC32K_SRC_SEL)
+ return sprintf(buf, "internal [external]\n");
+ else
+ return sprintf(buf, "[internal] external\n");
+}
+
+static ssize_t sunxi_rtc_store_clock_source(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count) {
+ struct sunxi_rtc_dev *chip = dev_get_drvdata(dev);
+ u32 val = readl(chip->base + SUNXI_LOSC_CTRL);
+
+ if (strncmp(buf, "external", 8) == 0)
+ val|=SUNXI_LOSC_OSC32K_SRC_SEL;
+ else if (strncmp(buf, "internal", 8) == 0)
+ val&=~SUNXI_LOSC_OSC32K_SRC_SEL;
+ else
+ return -EINVAL;
+
+ /* Writing this bit requires setting the upper 16 bit to 0x16aa (key
+ * value). */
+ val |= SUNXI_LOSC_KEY_VALUE;
+
+ writel(val, chip->base + SUNXI_LOSC_CTRL);
+ return count;
+}
+
+static DEVICE_ATTR(clock_source, S_IRUGO | S_IWUSR,
+ sunxi_rtc_show_clock_source,
+ sunxi_rtc_store_clock_source);
+
static int sunxi_rtc_probe(struct platform_device *pdev)
{
struct sunxi_rtc_dev *chip;
@@ -490,6 +536,13 @@ static int sunxi_rtc_probe(struct platform_device *pdev)
dev_info(&pdev->dev, "RTC enabled\n");
+ ret = device_create_file(&pdev->dev, &dev_attr_clock_source);
+ if (ret) {
+ dev_err(&pdev->dev, "Unable to create sysfs entry: %s\n",
+ dev_attr_clock_source.attr.name);
+ return ret;
+ }
+
return 0;
}
@@ -499,6 +552,7 @@ static int sunxi_rtc_remove(struct platform_device *pdev)
rtc_device_unregister(chip->rtc);
+ device_remove_file(&pdev->dev, &dev_attr_clock_source);
return 0;
}
--
2.2.0.34.gb8f29bf