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

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

Hi Marc,

On Mon, Jun 6, 2022 at 4:41 PM Marc Zyngier <maz@kernel.org> wrote:
>
> On Fri, 27 May 2022 12:05:38 +0100,
> "Lad, Prabhakar" <prabhakar.csengg@gmail.com> wrote:
> >
> > Hi,
> >
> > On Tue, May 24, 2022 at 6:22 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>
> > > ---
> > >  drivers/irqchip/Kconfig           |  1 +
> > >  drivers/irqchip/irq-sifive-plic.c | 71 ++++++++++++++++++++++++++++++-
> > >  2 files changed, 70 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
> > > index f3d071422f3b..aea0e4e7e547 100644
> > > --- a/drivers/irqchip/Kconfig
> > > +++ b/drivers/irqchip/Kconfig
> > > @@ -537,6 +537,7 @@ config SIFIVE_PLIC
> > >         bool "SiFive Platform-Level Interrupt Controller"
> > >         depends on RISCV
> > >         select IRQ_DOMAIN_HIERARCHY
> > > +       select IRQ_FASTEOI_HIERARCHY_HANDLERS
> > >         help
> > >            This enables support for the PLIC chip found in SiFive (and
> > >            potentially other) RISC-V systems.  The PLIC controls devices
> > > diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
> > > index bb87e4c3b88e..abffce48e69c 100644
> > > --- a/drivers/irqchip/irq-sifive-plic.c
> > > +++ b/drivers/irqchip/irq-sifive-plic.c
> > > @@ -60,10 +60,13 @@
> > >  #define        PLIC_DISABLE_THRESHOLD          0x7
> > >  #define        PLIC_ENABLE_THRESHOLD           0
> > >
> > > +#define RENESAS_R9A07G043_PLIC         1
> > > +
> > >  struct plic_priv {
> > >         struct cpumask lmask;
> > >         struct irq_domain *irqdomain;
> > >         void __iomem *regs;
> > > +       u8 of_data;
> > >  };
> > >
> > >  struct plic_handler {
> > > @@ -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);
> > > +
> > > +       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);
> > > +       }
> > > +}
> > > +
> > I sometimes still see an interrupt miss!
> >
> > As per [0], we first need to claim the interrupt by reading the claim
> > register which needs to be done in the ack callback (which should be
> > doable) for edge interrupts, but the problem arises in the chained
> > handler callback where it does claim the interrupt by reading the
> > claim register.
> >
> > static void plic_handle_irq(struct irq_desc *desc)
> > {
> >     struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
> >     struct irq_chip *chip = irq_desc_get_chip(desc);
> >     void __iomem *claim = handler->hart_base + CONTEXT_CLAIM;
> >     irq_hw_number_t hwirq;
> >
> >     WARN_ON_ONCE(!handler->present);
> >
> >     chained_irq_enter(chip, desc);
> >
> >     while ((hwirq = readl(claim))) {
> >         int err = generic_handle_domain_irq(handler->priv->irqdomain,
> >                             hwirq);
> >         if (unlikely(err))
> >             pr_warn_ratelimited("can't find mapping for hwirq %lu\n",
> >                     hwirq);
> >     }
> >
> >     chained_irq_exit(chip, desc);
> > }
> >
> > I was thinking I would get around by getting the irqdata in
> > plic_handle_irq() callback using the irq_desc (struct irq_data *d =
> > &desc->irq_data;) and check the d->hwirq but this will be always 9.
> >
> >         plic: interrupt-controller@12c00000 {
> >             compatible = "renesas-r9a07g043-plic";
> >             #interrupt-cells = <2>;
> >             #address-cells = <0>;
> >             riscv,ndev = <543>;
> >             interrupt-controller;
> >             reg = <0x0 0x12c00000 0 0x400000>;
> >             clocks = <&cpg CPG_MOD R9A07G043_NCEPLIC_ACLK>;
> >             clock-names = "plic100ss";
> >             power-domains = <&cpg>;
> >             resets = <&cpg R9A07G043_NCEPLIC_ARESETN>;
> >             interrupts-extended = <&cpu0_intc 11 &cpu0_intc 9>;
> >         };
> >
> > Any pointers on how this could be done sanely.
>
> Why doesn't the chained interrupt also get the ack-aware irq_chip?
>
Sorry for being naive, could you please elaborate on this.

Cheers,
Prabhakar

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

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