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

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Message-ID: <CAMuHMdWizSaABqAnwQi-Sa3ceiZV2CnAhiio4aCx_Bd7NvN1NQ@mail.gmail.com>
Date:   Wed, 25 May 2022 13:46:41 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Phil Edworthy <phil.edworthy@...esas.com>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH RFC 2/2] irqchip/sifive-plic: Add support for Renesas
 RZ/Five SoC

Hi Prabhakar,

On Wed, May 25, 2022 at 11:43 AM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
> On Wed, May 25, 2022 at 10:35 AM Geert Uytterhoeven
> <geert@...ux-m68k.org> wrote:
> > On Wed, May 25, 2022 at 11:01 AM Lad, Prabhakar
> > <prabhakar.csengg@...il.com> wrote:
> > > On Wed, May 25, 2022 at 9:01 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > > On Tue, May 24, 2022 at 7:22 PM Lad Prabhakar
> > > > <prabhakar.mahadev-lad.rj@...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@...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

Thanks, that was the missing piece!

Due to the new "select IRQ_FASTEOI_HIERARCHY_HANDLERS", I thought
your new call to handle_fasteoi_irq() had to be the first one in this
file...  But that config symbol protects handle_fasteoi_ack_irq(),
not handle_fasteoi_irq().

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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