clock offset may be set and read in decimal parts per billion
attribute is /sys/class/rtc/rtcN/offset
The attribute is only visible for rtcs that have set_offset implemented.
Signed-off-by: Joshua Clayton <stillcompiling@xxxxxxxxx>
---
Documentation/rtc.txt | 6 ++++++
drivers/rtc/rtc-sysfs.c | 35 ++++++++++++++++++++++++++++++++++-
2 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt
index 8446f1e..ddc3660 100644
--- a/Documentation/rtc.txt
+++ b/Documentation/rtc.txt
@@ -157,6 +157,12 @@ wakealarm: The time at which the clock will generate a system wakeup
the epoch by default, or if there's a leading +, seconds in the
future, or if there is a leading +=, seconds ahead of the current
alarm.
+offset: The amount which the rtc clock has been adjusted in firmware.
+ Visible only if the driver supports clock offset adjustment.
+ The unit is parts per billion, i.e. The number of clock ticks
+ which are added to or removed from the rtc's base clock per
+ billion ticks. A positive value makes a day pass more slowly,
+ longer, and a negative value makes a day pass more quickly.
IOCTL INTERFACE
---------------
diff --git a/drivers/rtc/rtc-sysfs.c b/drivers/rtc/rtc-sysfs.c
index 463e286..63b9fb1 100644
--- a/drivers/rtc/rtc-sysfs.c
+++ b/drivers/rtc/rtc-sysfs.c
@@ -218,6 +218,34 @@ wakealarm_store(struct device *dev, struct device_attribute *attr,
}
static DEVICE_ATTR_RW(wakealarm);
+static ssize_t
+offset_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+ ssize_t retval;
+ long offset;
+
+ retval = rtc_read_offset(to_rtc_device(dev), &offset);
+ if (retval == 0)
+ retval = sprintf(buf, "%ld\n", offset);
+
+ return retval;
+}
+
+static ssize_t
+offset_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t n)
+{
+ ssize_t retval;
+ long offset;
+
+ retval = kstrtol(buf, 10, &offset);
+ if (retval == 0)
+ retval = rtc_set_offset(to_rtc_device(dev), offset);
+
+ return (retval < 0) ? retval : n;
+}
+static DEVICE_ATTR_RW(offset);
+
static struct attribute *rtc_attrs[] = {
&dev_attr_name.attr,
&dev_attr_date.attr,
@@ -226,6 +254,7 @@ static struct attribute *rtc_attrs[] = {
&dev_attr_max_user_freq.attr,
&dev_attr_hctosys.attr,
&dev_attr_wakealarm.attr,
+ &dev_attr_offset.attr,
NULL,
};
@@ -249,9 +278,13 @@ static umode_t rtc_attr_is_visible(struct kobject *kobj,
struct rtc_device *rtc = to_rtc_device(dev);
umode_t mode = attr->mode;
- if (attr == &dev_attr_wakealarm.attr)
+ if (attr == &dev_attr_wakealarm.attr) {
if (!rtc_does_wakealarm(rtc))
mode = 0;
+ } else if (attr == &dev_attr_offset.attr) {
+ if (!rtc->ops->set_offset)
+ mode = 0;
+ }
return mode;
}
--
2.5.0
--
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