linux-kernel - Re: [PATCH 6/8] dt-bindings: interrupt-controller: RISC-V PLIC documentation

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Date:   Wed, 8 Aug 2018 10:15:58 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Christoph Hellwig <hch@....de>, Mark Rutland <mark.rutland@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Palmer Dabbelt <palmer@...ive.com>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Anup Patel <anup@...infault.org>, atish.patra@....com,
        devicetree@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-riscv@...ts.infradead.org, Stafford Horne <shorne@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [PATCH 6/8] dt-bindings: interrupt-controller: RISC-V PLIC documentation

On Wed, Aug 8, 2018 at 8:59 AM Christoph Hellwig <hch@....de> wrote:
>
> On Wed, Aug 08, 2018 at 08:29:50AM -0600, Rob Herring wrote:
> > Version numbers on the individual patches would be nice...
>
> We've never done these in the subsystems I'm involved with.  Too
> much clutter in the subject lines for information that is easily
> deductable.

Unfortunately not in Gmail which doesn't thread properly. But
patchwork also provides the version tag which I use to sort my
reviews.

> > > +Example:
> > > +
> > > +       plic: interrupt-controller@...0000 {
> > > +               #address-cells = <0>;
> > > +               #interrupt-cells = <1>;
> > > +               compatible = "riscv,plic0";
> > > +               interrupt-controller;
> > > +               interrupts-extended = <
> > > +                       &cpu0-intc 11
> > > +                       &cpu1-intc 11 &cpu1-intc 9
> > > +                       &cpu2-intc 11 &cpu2-intc 9
> > > +                       &cpu3-intc 11 &cpu3-intc 9
> > > +                       &cpu4-intc 11 &cpu4-intc 9>;
> >
> > I'm confused why this is still here if you are dropping the cpu intc binding?
>
> We need some parent that identifies the core (hart in RISC-V terminology).
> The way the code now works is that it just walks up the parent chain
> until it finds a CPU node, so it either accepts the legacy intc node
> inbetween, or it accepts the cpu node directly as the intc node is pointless.
>
> I guess for the documentation we should instead just point to the
> "riscv" cpu nodes instead?

That's not valid and dtc will tell you that. 'interrupts' (via
interrupt-parent) or 'interrupts-extended' has to point to an
'interrupt-controller' node. I guess you could make the cpu nodes
interrupt-controllers. That's a bit strange, but I can't think of a
reason why that wouldn't work.

Just because the cpu-intc is not made to be an irqchip in the kernel
doesn't mean it can't still be represented as an interrupt-controller
in DT. It shouldn't be designed just around how some OS happens to
implement things.

> > I also noticed the cpu binding refers to "riscv,cpu-intc" as well.
> > That needs to be fixed too if there's a change.
>
> Only in the examples.  I'd be fine with dropping them, but let's keep
> that separate from the interrupt support.

You need to sort out how this is all tied together and works because
right now you are supporting 2 ways and one is undocumented and the
other is invalid. Changing things later is only going to be more
painful.

Rob