Re: [PATCH V5 3/3] irqchip/sifive-plic: Fixup thead,c900-plic request_threaded_irq with ONESHOT

[Guo Ren]

On Mon, Oct 25, 2021 at 6:48 PM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> On Sun, 24 Oct 2021 02:33:03 +0100,
> guoren@xxxxxxxxxx wrote:
> >
> > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >
> > When using "devm_request_threaded_irq(,,,,IRQF_ONESHOT,,)" in the driver,
> > only the first interrupt could be handled, and continue irq is blocked by
> > hw. Because the thead,c900-plic couldn't complete masked irq source which
> > has been disabled in enable register. Add thead_plic_chip which fix up
> > c906-plic irq source completion problem by unmask/mask wrapper.
> >
> > Here is the description of Interrupt Completion in PLIC spec [1]:
> >
> > The PLIC signals it has completed executing an interrupt handler by
> > writing the interrupt ID it received from the claim to the claim/complete
> > register. The PLIC does not check whether the completion ID is the same
> > as the last claim ID for that target. If the completion ID does not match
> > an interrupt source that is currently enabled for the target, the
> >                          ^^ ^^^^^^^^^ ^^^^^^^
> > completion is silently ignored.
>
> Given this bit of the spec...
>
> > +static void plic_thead_irq_eoi(struct irq_data *d)
> > +{
> > +     struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
> > +
> > +     if (irqd_irq_masked(d)) {
> > +             plic_irq_unmask(d);
> > +             writel(d->hwirq, handler->hart_base + CONTEXT_CLAIM);
> > +             plic_irq_mask(d);
> > +     } else {
> > +             writel(d->hwirq, handler->hart_base + CONTEXT_CLAIM);
> > +     }
> > +}
> > +
>
> ... it isn't obvious to me why this cannot happen on an SiFive PLIC.
I'm not sure about SiFive PLIC. Maybe they didn't follow that to implement.

>
> And it isn't only for threaded interrupts in oneshot mode. Any driver
> can mask an interrupt from its handler after having set the
> IRQ_DISABLE_UNLAZY flag, and the interrupt would need the exact same
> treatment.
Thx for mentioned here, and I'll add it in the comment of next version patch.

>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/