[PATCH] rtc: Allow rtc drivers to specify the tv_nsec value for ntp

[J William Piggott]

On 11/23/2017 07:53 AM, Russell King - ARM Linux wrote:
> On Thu, Nov 23, 2017 at 01:04:51PM +0100, Alexandre Belloni wrote:
>>

 8<

>> But nothing prevents you from using hwclock every 11 minutes from
>> userspace. I really don't think this should be done from the kernel.
> 
> It's not just about running hwclock every 11 minutes.  It's about
> running hwclock when NTP sync'd.  If the local clock is not sync'd
> you don't want to be running hwclock, especially if you've trimmed
> the RTC.  So merely throwing hwclock -uw into a cron job really
> doesn't solve it.
> 
> A way around that would be to install adjtimex, so that the kernel's
> NTP flags can be read out.  However, that comes with its own set of
> problems.
> 
> On Debian, installing adjtimex will disrupt the timekeeping because
> of the post-install scripts debian runs.  It seems Debian assumes
> that if you install something, it has the right to modify the system
> timekeeping parameters immediately, screwing up ntpd in the process,
> if it's running.  The thought that you're installing adjtimex because
> you want to _inspect_ the kernel ntp parameters is not one that
> Debian folk appear to have considered as being a reason for installing
> the package.
> 

IMO, adjtimex is broken anyway. Use ntptime, it should be included
in the ntp package:

 $ /usr/sbin/ntptime | grep status
  status 0x40 (UNSYNC),

'ntptime -f ppm' allows correcting the system clock. So adjtimex really
isn't needed anymore.