svn commit: r354076 - head/sys/dev/ow
Ian Lepore
ian at freebsd.org
Fri Oct 25 16:06:48 UTC 2019
On Fri, 2019-10-25 at 19:03 +0300, Andriy Gapon wrote:
> On 25/10/2019 18:56, Ian Lepore wrote:
> > On Fri, 2019-10-25 at 18:51 +0300, Andriy Gapon wrote:
> > > On 25/10/2019 18:46, Ian Lepore wrote:
> > > > On Fri, 2019-10-25 at 15:38 +0000, Andriy Gapon wrote:
> > > > > Author: avg
> > > > > Date: Fri Oct 25 15:38:09 2019
> > > > > New Revision: 354076
> > > > > URL: https://svnweb.freebsd.org/changeset/base/354076
> > > > >
> > > > > Log:
> > > > > owc_gpiobus_read_data: compare times in sbintime_t units
> > > > >
> > > > > Previously the code used sbttous() before microseconds
> > > > > comparison
> > > > > in one
> > > > > place, sbttons() and nanoseconds in another, division by
> > > > > SBT_1US
> > > > > and
> > > > > microseconds in yet another.
> > > > >
> > > > > Now the code consistently uses multiplication by SBT_1US to
> > > > > convert
> > > > > microseconds to sbintime_t before comparing them with
> > > > > periods
> > > > > between
> > > > > calls to sbinuptime(). This is fast, this is precise
> > > > > enough
> > > > > (below
> > > > > 0.03%) and the periods defined by the protocol cannot
> > > > > overflow.
> > > > >
> > > > > Reviewed by: imp (D22108)
> > > > > MFC after: 2 weeks
> > > > >
> > > > > Modified:
> > > > > head/sys/dev/ow/owc_gpiobus.c
> > > > >
> > > > > Modified: head/sys/dev/ow/owc_gpiobus.c
> > > > > =============================================================
> > > > > ====
> > > > > ====
> > > > > =========
> > > > > --- head/sys/dev/ow/owc_gpiobus.c Fri Oct 25 15:02:50
> > > > > 2019 (
> > > > > r354
> > > > > 075)
> > > > > +++ head/sys/dev/ow/owc_gpiobus.c Fri Oct 25 15:38:09
> > > > > 2019 (
> > > > > r354
> > > > > 076)
> > > > > @@ -296,10 +296,10 @@ owc_gpiobus_read_data(device_t dev,
> > > > > struct
> > > > > ow_timing *
> > > > > do {
> > > > > now = sbinuptime();
> > > > > GETPIN(sc, &sample);
> > > > > - } while (sbttous(now - then) < t->t_rdv + 2 && sample
> > > > > == 0);
> > > > > + } while (now - then < (t->t_rdv + 2) * SBT_1US &&
> > > > > sample == 0);
> > > > > critical_exit();
> > > > >
> > > > > - if (sbttons(now - then) < t->t_rdv * 1000)
> > > > > + if (now - then < t->t_rdv * SBT_1US)
> > > > > *bit = 1;
> > > > > else
> > > > > *bit = 0;
> > > > > @@ -307,7 +307,7 @@ owc_gpiobus_read_data(device_t dev,
> > > > > struct
> > > > > ow_timing *
> > > > > /* Wait out the rest of t_slot */
> > > > > do {
> > > > > now = sbinuptime();
> > > > > - } while ((now - then) / SBT_1US < t->t_slot);
> > > > > + } while (now - then < t->t_slot * SBT_1US);
> > > > >
> > > > > RELBUS(sc);
> > > > >
> > > >
> > > > Unit conversions with sbt times should be done using the macros
> > > > that
> > > > carefully avoid roundoff errors. I don't understand why you've
> > > > changed
> > > > the code that correctly did use those macros to inline math.
> > >
> > > I think that the commit message explains it:
> > > This is fast, this is precise enough (below 0.03%) and the
> > > periods
> > > defined by
> > > the protocol cannot overflow.
> > >
> > > Do you disagree?
> > > Could you please explain in which of the three lines changed the
> > > new
> > > code is
> > > worse and why?
> > >
> >
> > I absolutely disagree (or I wouldn't have replied). Unit
> > conversions
> > using sbt times should use the predefined macros, NOT incline
> > multiplication and division. I don't know how to say it more
> > clearly
> > than that. The conversion macros are idiomatic (at least, they
> > would
> > be if people stopped writing inline conversion expressions).
>
> I can agree that I should have used ustosbt() instead of
> multiplication by
> SBT_1US, but I don't agree with your original message that I changed
> the code
> that correctly used the macros.
>
> But again, I know the times being converted, they are fixed by the
> protocol and
> I do not see why I have to use this:
>
> static __inline sbintime_t
> ustosbt(int64_t _us)
> {
> sbintime_t sb = 0;
>
> #ifdef KASSERT
> KASSERT(_us >= 0, ("Negative values illegal for ustosbt:
> %jd", _us));
> #endif
> if (_us >= SBT_1S) {
> sb = (_us / 1000000) * SBT_1S;
> _us = _us % 1000000;
> }
> /* 9223372036855 = ceil(2^63 / 1000000) */
> sb += ((_us * 9223372036855ull) + 0x7fffffff) >> 31;
> return (sb);
> }
>
> instead of this
> x * (((sbintime_t)1 << 32) / 1000000)
>
> The times:
> static struct ow_timing timing_regular = {
> .t_slot = 60, /* 60 to 120 */
> .t_low0 = 60, /* really 60 to 120 */
> .t_low1 = 1, /* really 1 to 15 */
> .t_release = 45, /* <= 45us */
> .t_rec = 1, /* at least 1us */
> .t_rdv = 15, /* 15us */
> .t_rstl = 480, /* 480us or more */
> .t_rsth = 480, /* 480us or more */
> .t_pdl = 60, /* 60us to 240us */
> .t_pdh = 60, /* 15us to 60us */
> .t_lowr = 1, /* 1us */
> };
>
>
The fact that you could say all that means that there is nothing I can
say that is going to change your mind. I will say if you ever do
anything like this to code I wrote, I will revert it immediately.
-- Ian
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