linux-kernel - Re: [PATCH v2 2/2] irqchip/sifive-plic: Add support for Renesas RZ/Five SoC

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Message-ID: <87a69y2z7a.wl-maz@kernel.org>
Date:   Mon, 27 Jun 2022 11:11:21 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH v2 2/2] irqchip/sifive-plic: Add support for Renesas RZ/Five SoC

On Mon, 27 Jun 2022 09:53:13 +0100,
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> 
> Hi Marc,
> 
> On Sun, Jun 26, 2022 at 2:19 PM Marc Zyngier <maz@...nel.org> wrote:
> > On Sun, 26 Jun 2022 10:38:18 +0100,
> > "Lad, Prabhakar" <prabhakar.csengg@...il.com> wrote:
> > > On Sun, Jun 26, 2022 at 9:56 AM Marc Zyngier <maz@...nel.org> wrote:
> > > > On Sun, 26 Jun 2022 01:43:26 +0100,
> > > > 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>
> 
> > > > > +     if (of_device_is_compatible(node, "renesas,r9a07g043-plic")) {
> > > > > +             priv->of_data = RENESAS_R9A07G043_PLIC;
> > > > > +             plic_chip.name = "Renesas RZ/Five PLIC";
> > > >
> > > > NAK. The irq_chip structure isn't the place for platform marketing.
> > > > This is way too long anyway (and same for the edge version), and you
> > > > even sent me a patch to make that structure const...
> > > >
> > > My bad will drop this.
> >
> > And why you're at it, please turn this rather random 'of_data' into
> > something like:
> >
> > diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
> > index bb87e4c3b88e..cd1683b77caf 100644
> > --- a/drivers/irqchip/irq-sifive-plic.c
> > +++ b/drivers/irqchip/irq-sifive-plic.c
> > @@ -64,6 +64,10 @@ struct plic_priv {
> >         struct cpumask lmask;
> >         struct irq_domain *irqdomain;
> >         void __iomem *regs;
> > +       enum {
> > +               VANILLA_PLIC,
> > +               RENESAS_R9A07G043_PLIC,
> > +       } flavour;
> >  };
> >
> >  struct plic_handler {
> >
> > to give some structure to the whole thing, because I'm pretty sure
> > we'll see more braindead implementations as time goes by.
> 
> What about using a feature flag (e.g. had_edge_irqs) instead?

Sure. Then make this an unsigned long, and have a set of quirk bits,
because I expect this to grow quickly.

>
> > It almost feels like I've written this whole patch. Oh wait...
> 
> > Without deviation from the norm, progress is not possible.
> 
> How applicable ;-)

I'm not sure there is any sign of progress here, and evolution
through random mutation has a pretty massive failure rate.

Thanks,

	M.

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