On Thu, 4 Feb 2016 23:07:54 +0100
Alexandre Belloni [off-list ref] wrote:

Hi,

On 03/02/2016 at 09:16:42 -0800, Joshua Clayton wrote :

quoted

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index 5836751..c064eb9 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c

@@ -939,4 +939,61 @@ void rtc_timer_cancel(struct rtc_device *rtc,

struct rtc_timer *timer) mutex_unlock(&rtc->ops_lock);
 }
 
+/**
+ * rtc_read_offset - Read the amount of rtc offset in parts per
billion
+ * @ rtc: rtc device to be used
+ * @ offset: the offset in parts per billion
+ *
+ * see below for details.
+ *
+ * Kernel interface to read rtc clock offset
+ * Returns 0 on success, or a negative number on error.
+ * If the rtc offset is not setable (or not implemented), return 0
and put
+ * 0 in the offset value;
+ */
+int rtc_read_offset(struct rtc_device *rtc, long *offset)
+{
+	int ret = 0;
+
+	if (!rtc->ops)
+		return -ENODEV;
+
+	if (!rtc->ops->set_offset) {
+		*offset = 0;
+		return 0;
+	}
+

I should have been clearer but this is not necessary anymore since the
sysfs interface will not always be present but you
should probably test rtc->ops->read_offset instead.

I left it because the kernel API is still there even if the sysfs
file is not...
but yeah, you are right. I'll fix the check, and the formatting
in the other patch.

quoted

+	mutex_lock(&rtc->ops_lock);
+	ret = rtc->ops->read_offset(rtc->dev.parent, offset);
+	mutex_unlock(&rtc->ops_lock);
+	return ret;
+}
 
+/**
+ * rtc_set_offset - Adjusts the duration of the average second
+ * @ rtc: rtc device to be used
+ * @ offset: the offset in parts per billion
+ *
+ * Some rtc's allow an adjustment to the average duration of a
second
+ * to compensate for differences in the actual clock rate due to
temperature,
+ * the crystal, capacitor, etc.
+ *
+ * Kernel interface to adjust an rtc clock offset.
+ * Return 0 on success, or a negative number on error.
+ * If the rtc offset is not setable (or not implemented), return
-EINVAL
+ */
+int rtc_set_offset(struct rtc_device *rtc, long offset)
+{
+	int ret = 0;
+
+	if (!rtc->ops)
+		return -ENODEV;
+
+	if (!rtc->ops->set_offset)
+		return -EINVAL;
+
+	mutex_lock(&rtc->ops_lock);
+	ret = rtc->ops->set_offset(rtc->dev.parent, offset);
+	mutex_unlock(&rtc->ops_lock);
+	return ret;
+}

diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 3359f04..b693ada 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h

@@ -89,6 +89,8 @@ struct rtc_class_ops {
 	int (*set_mmss)(struct device *, unsigned long secs);
 	int (*read_callback)(struct device *, int data);
 	int (*alarm_irq_enable)(struct device *, unsigned int

enabled);
+	int (*read_offset)(struct device *, long *offset);
+	int (*set_offset)(struct device *, long offset);
 };
 
 #define RTC_DEVICE_NAME_SIZE 20

@@ -208,6 +210,8 @@ void rtc_timer_init(struct rtc_timer *timer,

void (*f)(void *p), void *data); int rtc_timer_start(struct
rtc_device *rtc, struct rtc_timer *timer, ktime_t expires, ktime_t
period); void rtc_timer_cancel(struct rtc_device *rtc, struct
rtc_timer *timer); +int rtc_read_offset(struct rtc_device *rtc,
long *offset); +int rtc_set_offset(struct rtc_device *rtc, long
offset); void rtc_timer_do_work(struct work_struct *work);
 
 static inline bool is_leap_year(unsigned int year)
-- 
2.5.0

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