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

["Lad, Prabhakar" <prabhakar.csengg@gmail.com>]

Hi Geert,

On Wed, May 25, 2022 at 10:35 AM Geert Uytterhoeven
<geert@linux-m68k.org> wrote:
>
> 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?
>
For non RZ/Five, handle_fasteoi_irq() [0] is used for both edge/level
interrupts.

[0] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/irqchip/irq-sifive-plic.c?h=next-20220525#n195

> 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.
>
Ok I will update this in v2.

Cheers,
Prabhakar

> 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