rtc: add procfs sysctl to control RTC updates

Add a procfs sysctl to allow the RTC updates by the NTP code to be
disabled.

This is necessary if one wishes to adjust the RTC trimming.  When
performing such an adjustment, one would want to compare the RTC
against a good reference.  One way to do that is to synchronise the
systems own time using NTP, but doing so causes the kernel to set
the RTC every 11 minutes.

This repeated setting prevents measuring the long-term drift of the
RTC, and so prevents any attempt to trim the RTC for better accuracy.

This sysctl defaults to enabled, so existing behaviour is preserved.
When one wishes to adjust the long-term drift, the RTC update can be
disabled via: echo 0 > /proc/sys/kernel/ntp_rtc_sync, the drift
measured, and the update subsequently re-enabled.  The next update
will be triggered by the next successful adjtimex call.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

0 files changed, 0 insertions, 0 deletions