On Tue, Oct 03, 2017 at 03:31:58PM +0200, Alexandre Belloni wrote: > 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. That sounds like a nightmare - stuff should be documented in detail in one place and only one place, otherwise we risk the two sets of identical documentation going out of sync. A better idea would be to reference the detailed documentation - which I guess would be easier if rtc.txt were converted to a .rst file? -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up
