Re: [RFC PATCH] rtc: add rtc_systohc for ntp use

[David Woodhouse <dwmw2@infradead.org>]

On Mon, 2008-11-10 at 16:40 +0100, Alessandro Zummo wrote:
> Adds in-kernel hctosys functionality that can
> be used by ntp sync code.
> 
> This is an RFC and has not been tested, I just want
> to check if something similar could solve the problems
> of those who want the NTP sync mode.

You might do better to open the device once and keep it open, rather
than taking the mutex and opening it again _during_ each call? You're
going to be perturbing the timing by doing that.

I believe you were also concerned that some device wouldn't want the
behaviour given by the existing sync_cmos_clock() function and workqueue
stuff in kernel/ntp.c, where we update the clock precisely half-way
through the second?

We should probably rip that code out of ntp.c (or just disable it ifdef
CONFIG_RTC_CLASS), and provide our own version of notify_cmos_timer().

The workqueue stuff to trigger at half-past the second could be kept as
a library function which most RTC devices would use, but they'd have the
option to use their own instead.

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation