[PATCH v2 7/8] rtc: implement a sysfs interface for clock offset

[Joshua Clayton <stillcompiling@gmail.com>]

The file is called "offset", and may be set and read in decimal.
For rtcs that do not have read_offset or set_offset implemented,
read always returns zero and write will return -EINVAL.

Signed-off-by: Joshua Clayton <stillcompiling@gmail.com>
---
 drivers/rtc/interface.c |  2 +-
 drivers/rtc/rtc-sysfs.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index 57cd928..c064eb9 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -959,7 +959,7 @@ int rtc_read_offset(struct rtc_device *rtc, long *offset)
 		return -ENODEV;
 
 	if (!rtc->ops->set_offset) {
-		offset = 0;
+		*offset = 0;
 		return 0;
 	}
 
diff --git a/drivers/rtc/rtc-sysfs.c b/drivers/rtc/rtc-sysfs.c
index 7273855..622a0dc 100644
--- a/drivers/rtc/rtc-sysfs.c
+++ b/drivers/rtc/rtc-sysfs.c
@@ -211,6 +211,34 @@ 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,
@@ -219,6 +247,7 @@ static struct attribute *rtc_attrs[] = {
 	&dev_attr_max_user_freq.attr,
 	&dev_attr_hctosys.attr,
 	&dev_attr_wakealarm.attr,
+	&dev_attr_offset.attr,
 	NULL,
 };
 
-- 
2.5.0