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    SubjectRe: [PATCHv3 12/16] ntp: add hardpps implementation
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    On Thu, 2010-08-05 at 01:06 +0400, Alexander Gordeev wrote:
    > This commit adds hardpps() implementation based upon the original one
    > from the NTPv4 reference kernel code from David Mills. However, it is
    > highly optimized towards very fast syncronization and maximum stickness
    > to PPS signal. The typical error is less then a microsecond.
    > To make it sync faster I had to throw away exponential phase filter so
    > that the full phase offset is corrected immediately. Then I also had to
    > throw away median phase filter because it gives a bigger error itself
    > if used without exponential filter.
    > Maybe we will find an appropriate filtering scheme in the future but
    > it's not necessary if the signal quality is ok.
    >
    > Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>

    [snip]

    > +#ifdef CONFIG_NTP_PPS
    > +
    > +struct pps_normtime {
    > + __kernel_time_t sec; /* seconds */
    > + long nsec; /* nanoseconds */
    > +};

    I don't quite remember the history here (it may be I suggested you use
    this instead of overloading a timespec? I honestly don't recall), but
    could you add some extra context in a comment here for what a
    pps_normtime structure represents and why its used instead of a
    timespec? The comment below sort of hints at it, but it would be useful
    if it was more explicit.

    > +/* normalize the timestamp so that nsec is in the
    > + ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
    > +static inline struct pps_normtime pps_normalize_ts(struct timespec ts)
    > +{
    > + struct pps_normtime norm = {
    > + .sec = ts.tv_sec,
    > + .nsec = ts.tv_nsec
    > + };
    > +
    > + if (norm.nsec > (NSEC_PER_SEC >> 1)) {
    > + norm.nsec -= NSEC_PER_SEC;
    > + norm.sec++;
    > + }
    > +
    > + return norm;
    > +}

    Otherwise the code looks pretty good to me.

    Acked-by: John Stultz <johnstul@us.ibm.com>

    thanks
    -john




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