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Commit 8a25c8f6 authored by Russell King's avatar Russell King Committed by Alexandre Belloni
Browse files

rtc: clarify the RTC offset correction 



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: default avatarRussell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: default avatarAlexandre Belloni <alexandre.belloni@free-electrons.com>
parent 9d7ed21f

drivers/rtc/interface.c

+4 −0
Original line number Diff line number Diff line
@@ -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

 *

 * 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