Re: [PATCH RFC 2/2] irqchip/sifive-plic: Add support for Renesas RZ/Five SoC

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Prabhakar,

On Wed, May 25, 2022 at 11:01 AM Lad, Prabhakar
<prabhakar.csengg@gmail.com> wrote:
> On Wed, May 25, 2022 at 9:01 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Tue, May 24, 2022 at 7:22 PM Lad Prabhakar
> > <prabhakar.mahadev-lad.rj@bp.renesas.com> wrote:
> > > The Renesas RZ/Five SoC has a RISC-V AX45MP AndesCore with NCEPLIC100. The
> > > NCEPLIC100 supports both edge-triggered and level-triggered interrupts. In
> > > case of edge-triggered interrupts NCEPLIC100 ignores the next interrupt
> > > edge until the previous completion message has been received and
> > > NCEPLIC100 doesn't support pending interrupt counter, hence losing the
> > > interrupts if not acknowledged in time.
> > >
> > > So the workaround for edge-triggered interrupts to be handled correctly
> > > and without losing is that it needs to be acknowledged first and then
> > > handler must be run so that we don't miss on the next edge-triggered
> > > interrupt.
> > >
> > > This patch adds a new compatible string for Renesas RZ/Five SoC and adds
> > > support to change interrupt flow based on the interrupt type. It also
> > > implements irq_ack and irq_set_type callbacks.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> >
> > Thanks for your patch!
> >
> > > --- a/drivers/irqchip/irq-sifive-plic.c
> > > +++ b/drivers/irqchip/irq-sifive-plic.c

> > > @@ -163,10 +166,31 @@ static int plic_set_affinity(struct irq_data *d,
> > >  }
> > >  #endif
> > >
> > > +static void plic_irq_ack(struct irq_data *d)
> > > +{
> > > +       struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
> > > +
> >
> > No check for RZ/Five or irq type?
> That is because we set the handle_fasteoi_ack_irq() only in case of
> RZ/Five and it is already checked in set_type() callback.
>
> > .irq_ack() seems to be called for level interrupts, too
> > (from handle_level_irq() through mask_ack_irq()).
> >
> Right but we are using handle_fasteoi_irq() for level interrupt which
> doesn't call mask_ack_irq(). And I have confirmed by adding a print in
> ack callback  and just enabling the serial (which has level
> interrupts).

But handle_fasteoi_irq() is configured only on RZ/Five below?
Which handler is used on non-RZ/Five?

I have to admit I'm not that deep into irq handling, and
adding a print indeed doesn't trigger on Starlight Beta.

> > > @@ -176,11 +200,37 @@ static void plic_irq_eoi(struct irq_data *d)
> > >         }
> > >  }
> > >
> > > +static int plic_irq_set_type(struct irq_data *d, unsigned int type)
> > > +{
> > > +       struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
> > > +
> > > +       if (handler->priv->of_data != RENESAS_R9A07G043_PLIC)
> > > +               return 0;
> > > +
> > > +       switch (type) {
> > > +       case IRQ_TYPE_LEVEL_HIGH:
> > > +               irq_set_handler_locked(d, handle_fasteoi_irq);
> > > +               break;
> > > +
> > > +       case IRQ_TYPE_EDGE_RISING:
> > > +               irq_set_handler_locked(d, handle_fasteoi_ack_irq);
> > > +               break;
> > > +
> > > +       default:
> > > +               return -EINVAL;
> > > +       }
> > > +
> > > +       return 0;
> > > +}
> > > +
> > >  static struct irq_chip plic_chip = {
> > >         .name           = "SiFive PLIC",
> > >         .irq_mask       = plic_irq_mask,
> > >         .irq_unmask     = plic_irq_unmask,
> > > +       .irq_ack        = plic_irq_ack,
> >
> > This causes extra processing on non-affected PLICs.
> > Perhaps use a separate irq_chip instance?
> >
> I don't think so as the handle_fasteoi_ack_irq() is installed only in
> case of RZ/Five, so irq_ack() will not be called for non-affected
> PLIC's. Please correct me if I am wrong.

Hence I'll leave this to the irq maintainer...

> > > @@ -293,6 +356,9 @@ static int __init plic_init(struct device_node *node,
> > >         if (!priv)
> > >                 return -ENOMEM;
> > >
> > > +       if (of_device_is_compatible(node, "renesas-r9a07g043-plic"))
> > > +               priv->of_data = RENESAS_R9A07G043_PLIC;
> > > +
> >
> > So perhaps instead just look at #interrupt-cells, and use the onecell
> > or twocell irq_chip/irq_domain_ops based on that?
> >
> But we do call plic_irq_domain_translate() in the alloc callback and
> don't have a node pointer in there to check the interrupt cell count.
> Or maybe we can store the interrupt cell count in priv and use it
> accordingly above?

That's a reasonable option.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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