RE: [PATCH net] ptp: netc: fix period truncation and potential divide-by-zero in PEROUT

> 
> On 26-08-21 01:52:37, Wei Fang wrote:
> >
> > NXP Confidential
> 
> Which part is confidential ?

Sorry, the company's email policy has been updated, and this label needs
to be manually deleted, but I didn't notice. :(


> 
> > > On Tue, Aug 18, 2026 at 11:33:41AM +0800, [email protected] wrote:
> > > > From: Wei Fang <[email protected]>
> > > >
> > > > The max_period bound in net_timer_enable_perout() was computed as:
> > > >
> > > >   max_period = (u64)NETC_TMR_DEFAULT_FIPER + integral_period;
> > > >
> > > > which exceeds U32_MAX when integral_period > 0 (e.g. 0x100000002
> > > > for the default 333333333 Hz clock). A period_ns that passes this
> > > > check but exceeds U32_MAX is then silently truncated when stored
> > > > into the u32 struct netc_pp::period field.
> > > >
> > > > A truncated value of zero can reach netc_timer_set_perout_alarm(),
> > > > where the local u32 period variable would also be 0, causing a
> > > > divide-by-zero in roundup_u64(delta, period) whenever the stime <
> > > > min_time branch is taken (which always happens for a start time of {0, 0}).
> > > >
> > > > Additionally, netc_timer_enable_periodic_pulse() and
> > > > netc_timer_enable_fiper() both compute:
> > > >
> > > >   fiper = pp->period - integral_period;
> > > >
> > > > A zero pp->period results in an unsigned wraparound to 0xFFFFFFFD,
> > > > mis-programming the FIPER hardware register.
> > > >
> > > > Fix all three issues by capping max_period at
> > > > NETC_TMR_DEFAULT_FIPER (0xFFFFFFFF). This ensures that any
> > > > period_ns passing the range check fits in a u32 without
> > > > truncation, so the stored value is always valid and non-zero. The
> > > > accepted range is reduced by integral_period ns (typically only a few
> nanoseconds), which is negligible in practice.
> > > >
> > > > Fixes: 671e266835b8 ("ptp: netc: add periodic pulse output
> > > > support")
> > > > Signed-off-by: Wei Fang <[email protected]>
> > >
> > > If so, then I think NETC_TMR_DEFAULT_FIPER can simply be used in
> > > place of max_period.
> >
> > Yes, I also considered this modification, but ultimately chose this
> > lazy approach. Since you brought it up, I will improve it in the next version.
> > Thanks. :)
> 
> Hopefully, not the lazy part. ;-)