On Fri, Sep 09, 2022 at 03:59:01PM +1000, Jonathan Gray wrote:
> On Thu, Sep 08, 2022 at 08:31:21PM -0500, Scott Cheloha wrote:
> > On Sat, Aug 27, 2022 at 09:28:06PM -0500, Scott Cheloha wrote:
> > > Whoops, forgot about the split read problem. My mistake.
> > >
> > > Because 32-bit platforms cannot do bus_space_read_8 atomically, and
> > > i386 can use acpihpet(4), we can only safely use the lower 32 bits of
> > > the counter in acpihpet_delay() (unless we want two versions of
> > > acpihpet_delay()... which I don't).
> > >
> > > Switch from acpihpet_r() to bus_space_read_4(9) and accumulate cycles
> > > as we do in acpihpet_delay(). Unlike acpitimer(4), the HPET is a
> > > 64-bit counter so we don't need to mask the difference between val1
> > > and val2.
> > >
> > > [...]
> >
> > 12 day ping.
> >
> > This needs fixing before it causes problems.
>
> the hpet spec says to set a bit to force a 32-bit counter on
> 32-bit platforms
>
> see 2.4.7 Issues related to 64-bit Timers with 32-bit CPUs, in
> https://www.intel.com/content/dam/www/public/us/en/documents/technical-specifications/software-developers-hpet-spec-1-0a.pdf
I don't follow your meaning. Putting the HPET in 32-bit mode doesn't
help us here, it would just break acpihpet_delay() in a different way.
The problem is that acpihpet_delay() is written as a 64-bit delay(9)
and there's no way to do that safely on i386 without introducing extra
overhead.
The easiest and cheapest fix is to rewrite acpihpet_delay() as a
32-bit delay(9), i.e. we count cycles until we pass a threshold.
acpitimer_delay() in acpi/acpitimer.c is a 32-bit delay(9) and it
works great, let's just do the same thing again here.
ok?
Index: acpihpet.c
===================================================================
RCS file: /cvs/src/sys/dev/acpi/acpihpet.c,v
retrieving revision 1.28
diff -u -p -r1.28 acpihpet.c
--- acpihpet.c 25 Aug 2022 18:01:54 -0000 1.28
+++ acpihpet.c 9 Sep 2022 12:29:41 -0000
@@ -281,13 +281,19 @@ acpihpet_attach(struct device *parent, s
void
acpihpet_delay(int usecs)
{
- uint64_t c, s;
+ uint64_t count = 0, cycles;
struct acpihpet_softc *sc = hpet_timecounter.tc_priv;
+ uint32_t val1, val2;
- s = acpihpet_r(sc->sc_iot, sc->sc_ioh, HPET_MAIN_COUNTER);
- c = usecs * hpet_timecounter.tc_frequency / 1000000;
- while (acpihpet_r(sc->sc_iot, sc->sc_ioh, HPET_MAIN_COUNTER) - s < c)
+ val2 = bus_space_read_4(sc->sc_iot, sc->sc_ioh, HPET_MAIN_COUNTER);
+ cycles = usecs * hpet_timecounter.tc_frequency / 1000000;
+ while (count < cycles) {
CPU_BUSY_CYCLE();
+ val1 = val2;
+ val2 = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
+ HPET_MAIN_COUNTER);
+ count += val2 - val1;
+ }
}
u_int
