netdev - Re: [PATCH net] ptp: ocp: have adjtime handle negative delta

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Date:   Sat, 7 May 2022 21:55:07 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Vadim Fedorenko <vfedorenko@...ek.ru>
Cc:     netdev@...r.kernel.org, richardcochran@...il.com,
        kernel-team@...com, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com
Subject: Re: [PATCH net] ptp: ocp: have adjtime handle negative delta_ns
 correctly

On Sat, May 07, 2022 at 01:19:54AM +0100, Vadim Fedorenko wrote:
> On 06.05.2022 00:40, Jonathan Lemon wrote:
> > delta_ns is a s64, but it was being passed ptp_ocp_adjtime_coarse
> > as an u64.  Also, it turns out that timespec64_add_ns() only handles
> > positive values, so the math needs to be updated.
> > 
> > Fix by passing in the correct signed value, then adding to a
> > nanosecond version of the timespec.
> > 
> > Fixes: '90f8f4c0e3ce ("ptp: ocp: Add ptp_ocp_adjtime_coarse for large adjustments")'
> > Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> > ---
> >   drivers/ptp/ptp_ocp.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
> > index dd45471f6780..65e592ec272e 100644
> > --- a/drivers/ptp/ptp_ocp.c
> > +++ b/drivers/ptp/ptp_ocp.c
> > @@ -841,16 +841,18 @@ __ptp_ocp_adjtime_locked(struct ptp_ocp *bp, u32 adj_val)
> >   }
> >   static void
> > -ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, u64 delta_ns)
> > +ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, s64 delta_ns)
> >   {
> >   	struct timespec64 ts;
> >   	unsigned long flags;
> >   	int err;
> > +	s64 ns;
> >   	spin_lock_irqsave(&bp->lock, flags);
> >   	err = __ptp_ocp_gettime_locked(bp, &ts, NULL);
> >   	if (likely(!err)) {
> > -		timespec64_add_ns(&ts, delta_ns);
> > +		ns = timespec64_to_ns(&ts) + delta_ns;
> > +		ts = ns_to_timespec64(ns);
> 
> Maybe use set_normalized_timespec64 instead of this ugly transformations and
> additional variable?

I don't see how that would work - set_normalized_timespec64 just sets
the ts from a <sec>.<nsec> value.  In this case, delta_ns need to be
added in to the ts value, but timespec64_add_ns() doeesn't handle
negative values, hence the conversion / add / reconversion.
-- 
Jonathan