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

[Palmer Dabbelt]

On Wed, 08 Aug 2018 09:15:58 PDT (-0700), robh+dt@xxxxxxxxxx wrote:
> On Wed, Aug 8, 2018 at 8:59 AM Christoph Hellwig <hch@xxxxxx> 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@c000000 {
> > > > +               #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