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rtc: implement a sysfs interface for clock offset 

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@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
This commit is contained in:
Joshua Clayton 2016-02-05 12:41:12 -08:00 committed by Alexandre Belloni
parent b3967067c2
commit 5495a4159f
2 changed files with 40 additions and 1 deletions
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6
Documentation/rtc.txt
View File

@ -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
---------------

35
drivers/rtc/rtc-sysfs.c
View File

@ -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;
}