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

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Date:   Wed, 08 Aug 2018 13:49:37 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     robh+dt@...nel.org
CC:     Christoph Hellwig <hch@....de>, mark.rutland@....com,
        tglx@...utronix.de, jason@...edaemon.net, marc.zyngier@....com,
        anup@...infault.org, atish.patra@....com,
        devicetree@...r.kernel.org, aou@...s.berkeley.edu,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        shorne@...il.com
Subject:     Re: [PATCH 6/8] dt-bindings: interrupt-controller: RISC-V PLIC documentation

On Wed, 08 Aug 2018 09:15:58 PDT (-0700), robh+dt@...nel.org wrote:
> 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.

FWIW, I like this approach.  There is an interrupt widget in the hardware, so 
having the device tree represent it seems like a good idea.

>> > 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