AW: [PATCH] kern_tc.c: Update pps_event() for uniprocessor configurations

[Gabriel.Moyano at dlr.de]

> On 30/05/2022 09:29, Gabriel Moyano wrote:
> > Since pps->capgen is not used in uniprocessor configurations, there is
> > no need to verified if it is equal to zero
> >
> > Update #2349
> > ---
> >   cpukit/score/src/kern_tc.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/cpukit/score/src/kern_tc.c b/cpukit/score/src/kern_tc.c
> > index 92739d8edd..897f81511e 100644
> > --- a/cpukit/score/src/kern_tc.c
> > +++ b/cpukit/score/src/kern_tc.c
> > @@ -2165,7 +2165,11 @@ pps_event(struct pps_state *pps, int event)
> >   	if ((event & pps->ppsparam.mode) == 0)
> >   		return;
> >   	/* If the timecounter was wound up underneath us, bail out. */
> > +#if defined(RTEMS_SMP)
> >   	if (pps->capgen == 0 || pps->capgen !=
> > +#else
> > +	if (pps->capgen !=
> > +#endif
> >   	    atomic_load_acq_int(&pps->capth->th_generation))
> >   		return;
> >
> 
> I think this fix is incomplete. What is with:
> 
> void
> pps_capture(struct pps_state *pps)
> {
> 	struct timehands *th;
> 
> 	KASSERT(pps != NULL, ("NULL pps pointer in pps_capture"));
> 	th = timehands;
> 	pps->capgen = atomic_load_acq_int(&th->th_generation);
> 	pps->capth = th;
> #ifdef FFCLOCK
> 	pps->capffth = fftimehands;
> #endif
> 	pps->capcount = th->th_counter->tc_get_timecount(th->th_counter);
> 	atomic_thread_fence_acq();
> 	if (pps->capgen != th->th_generation)
> 		pps->capgen = 0;
> }
> 
> I don't know why there is this "if" in the code. I will ask on a FreeBSD mailing list.
> 

I think it is for the case that th_generation has changed in between saving the th and th_counter. If this happens pps->capgen is set to 0 and later pps_event() returns earlier. Since for uniprocessor th_generation equal to 0 is not used, I guess we can removed this if for those configurations