Hi, On 29/09/2017 at 11:23:25 +0100, Russell King wrote: > The RTC offset correction documentation is not very clear about the > exact relationship between "offset" and the effect it has on the RTC. > Supplement the documentation with an equation giving the relationship. > > Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx> > --- > drivers/rtc/interface.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c > index 8cec9a02c0b8..045e0a72d14b 100644 > --- a/drivers/rtc/interface.c > +++ b/drivers/rtc/interface.c > @@ -1004,6 +1004,10 @@ int rtc_read_offset(struct rtc_device *rtc, long *offset) > * to compensate for differences in the actual clock rate due to temperature, > * the crystal, capacitor, etc. > * > + * The adjustment applied is as follows: > + * t = t0 * (1 + offset * 1e-9) > + * where t0 is the measured length of 1 RTC second with offset = 0 > + * More documentation is available in Documentation/rtc.txt. Maybe it is worth having the formula in both. > * 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 > -- > 2.7.4 > -- Alexandre Belloni, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
