On Thu, 14 Aug 2025 11:49:26 +0100,
Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> On Thu, 14 Aug 2025 11:13:47 +0100,
> Steven Price <steven.price@xxxxxxx> wrote:
> >
> > On 07/08/2025 17:02, Marc Zyngier wrote:
> > > Add a new driver for the MMIO side of the ARM architected timer.
> > > Most of it has been lifted from the existing arch timer code,
> > > massaged, and finally rewritten.
> > >
> > > It supports both DT and ACPI as firmware descriptions.
> > >
> > > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > > ---
> > > MAINTAINERS | 1 +
> > > drivers/clocksource/arm_arch_timer_mmio.c | 420 ++++++++++++++++++++++
> > > 2 files changed, 421 insertions(+)
> > > create mode 100644 drivers/clocksource/arm_arch_timer_mmio.c
> > >
> > [...]
> > > +static void arch_timer_mmio_setup(struct arch_timer *at, int irq)
> > > +{
> > > + at->evt = (struct clock_event_device) {
> > > + .features = (CLOCK_EVT_FEAT_ONESHOT |
> > > + CLOCK_EVT_FEAT_DYNIRQ),
> > > + .name = "arch_mem_timer",
> > > + .rating = 400,
> > > + .cpumask = cpu_possible_mask,
> > > + .irq = irq,
> > > + .set_next_event = arch_timer_mmio_set_next_event,
> > > + .set_state_oneshot_stopped = arch_timer_mmio_shutdown,
> > > + .set_state_shutdown = arch_timer_mmio_shutdown,
> > > + };
> > > +
> > > + at->evt.set_state_shutdown(&at->evt);
> > > +
> > > + clockevents_config_and_register(&at->evt, at->rate, 0xf, CLOCKSOURCE_MASK(56));
> >
> > This doesn't work on 32 bit - clockevents_config_and_register()'s final
> > argument is an unsigned long, and a 56 bit mask doesn't fit. This
> > triggers a compiler warning:
>
> Already reported, see 20250814111657.7debc9f1@xxxxxxxxxxxxxxxx.
>
> > Possible this should really be min(CLOCKSOURCE_MASK(56), ULONG_MAX)? But
> > I'm not familiar enough with this code. Most likely it's dead code on a
> > 32 bit platform.
>
> No, this definitely exists on 32bit crap, since it has been part of
> the architecture from the ARMv7+VE days.
>
> I think this is more of an impedance mismatch between the
> CLOCKSOURCE_MASK() helper and the clockevents_config_and_register(),
> and a (unsigned long) cast would do the trick.
Of course not. That would just result in a big fat zero.
> But it also means that the per-cpu timer also gets truncated the same
> way, and that has interesting impacts on how often the timer is
> reprogrammed.
That question still stand, and I wonder whether we have ugly bugs
lurking on 32bit platforms because of that... I'll try and have a
look.
M.
--
Jazz isn't dead. It just smells funny.
