Re: [RFC PATCH 03/13] target/ppc: move interrupt masking out of ppc_hw_interrupt

[Matheus K. Ferst]

On 15/08/2022 17:09, Fabiano Rosas wrote:
> Matheus Ferst <matheus.ferst@eldorado.org.br> writes:
>
> > Move the interrupt masking logic to a new method, ppc_pending_interrupt,
> > and only handle the interrupt processing in ppc_hw_interrupt.
> >
> > Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
> > ---
> >   target/ppc/excp_helper.c | 228 ++++++++++++++++++++++++---------------
> >   1 file changed, 141 insertions(+), 87 deletions(-)
> >
> > diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
>
> <snip>
>
> > @@ -1884,15 +1915,38 @@ bool ppc_cpu_exec_interrupt(CPUState *cs, int 
> > interrupt_request)
> >   {
> >       PowerPCCPU *cpu = POWERPC_CPU(cs);
> >       CPUPPCState *env = &cpu->env;
> > +    int pending_interrupt;
>
> I would give this a simpler name to avoid confusion with the other two
> pending_interrupt terms.
>
> > -    if (interrupt_request & CPU_INTERRUPT_HARD) {
> > -        ppc_hw_interrupt(env);
> > -        if (env->pending_interrupts == 0) {
> > -            cs->interrupt_request &= ~CPU_INTERRUPT_HARD;
> > -        }
> > -        return true;
> > +    if ((interrupt_request & CPU_INTERRUPT_HARD) == 0) {
> > +        return false;
> >       }
> > -    return false;
> > +
>
> It seems we're assuming that after this point we certainly have some
> pending interrupt...
>
> > +    pending_interrupt = ppc_pending_interrupt(env);
> > +    if (pending_interrupt == 0) {
>
> ...but how then is this able to return 0?

At this point in the patch series, raising interrupts with ppc_set_irq 
always sets CPU_INTERRUPT_HARD, so it is possible that all interrupts 
are masked, and then ppc_pending_interrupt would return zero.

> Could the function's name be
> made a bit clearer? Maybe interrupt = ppc_next_pending_interrupt or
> something to that effect.

Maybe ppc_next_unmasked_interrupt?

> > +        if (env->resume_as_sreset) {
> > +            /*
> > +             * This is a bug ! It means that has_work took us out of halt
> > +             * without anything to deliver while in a PM state that requires
> > +             * getting out via a 0x100
> > +             *
> > +             * This means we will incorrectly execute past the power management
> > +             * instruction instead of triggering a reset.
> > +             *
> > +             * It generally means a discrepancy between the wakeup conditions 
> > in
> > +             * the processor has_work implementation and the logic in this
> > +             * function.
> > +             */
> > +            cpu_abort(env_cpu(env),
> > +                      "Wakeup from PM state but interrupt Undelivered");
>
> This condition is BookS only. Perhaps it would be better to move it
> inside each of the processor-specific functions. And since you're
> merging has_work with pending_interrupts, can't you solve that issue
> earlier? Specifically the "has_work tooks us out of halt..." part.

This condition would not be an error in ppc_pending_interrupt because 
we'll call this method from other places in the following patches, like 
ppc_set_irq. Maybe we should move it to a "case 0:" in ppc_hw_interrupt?

> > +        }
> > +        return false;
> > +    }
> > +
> > +    ppc_hw_interrupt(env, pending_interrupt);
>
> Some verbs would be nice. ppc_deliver_interrupt?

Agreed. Should we also make processor-specific versions of this method? 
That way, we could get rid of the calls to ppc_decr_clear_on_delivery 
and is_book3s_arch2x.

> > +    if (env->pending_interrupts == 0) {
> > +        cpu_reset_interrupt(cs, CPU_INTERRUPT_HARD);
> > +    }
> > +    return true;
> >   }
> >
> >   #endif /* !CONFIG_USER_ONLY */

Thanks,
Matheus K. Ferst
Instituto de Pesquisas ELDORADO <http://www.eldorado.org.br/>
Analista de Software
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