diff options
author | Joshua Clayton <stillcompiling@gmail.com> | 2016-02-05 12:41:11 -0800 |
---|---|---|
committer | Alexandre Belloni <alexandre.belloni@free-electrons.com> | 2016-03-14 17:08:15 +0100 |
commit | b3967067c273359c7462f4be9a887c3d1a515f49 (patch) | |
tree | 1f2ca90d34dae4961b97d68ccdb93a979ee5e2b8 /drivers/rtc | |
parent | 9d1fa4c3737ac82520931d940dcd2426719f8dd2 (diff) | |
download | linux-b3967067c273359c7462f4be9a887c3d1a515f49.tar.bz2 |
rtc: Add functions to set and read rtc offset
A number of rtc devices, such as the NXP pcf2123 include a facility
to adjust the clock in order to compensate for temperature or a
crystal, capacitor, etc, that results in the rtc clock not running
at exactly 32.768 kHz.
Data sheets I have seen refer to this as a clock offset, and measure it
in parts per million, however they often reference ppm to 2 digits of
precision, which makes integer ppm less than ideal.
We use parts per billion, which more than covers the precision needed
and works nicely within 32 bits
Signed-off-by: Joshua Clayton <stillcompiling@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Diffstat (limited to 'drivers/rtc')
-rw-r--r-- | drivers/rtc/interface.c | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c index 5836751b8203..9ef5f6f89f98 100644 --- a/drivers/rtc/interface.c +++ b/drivers/rtc/interface.c @@ -939,4 +939,58 @@ 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 read_offset() is not implemented for the rtc, return -EINVAL + */ +int rtc_read_offset(struct rtc_device *rtc, long *offset) +{ + int ret; + + if (!rtc->ops) + return -ENODEV; + + if (!rtc->ops->read_offset) + return -EINVAL; + + 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; + + 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; +} |