Re: [PATCH 03/12] of: Add binding document for MIPS GIC

[David Daney]

On 09/03/2014 04:53 PM, Andrew Bresticker wrote:
> On Tue, Sep 2, 2014 at 5:50 PM, David Daney <ddaney.cavm@xxxxxxxxx> wrote:
[...]
> > Your comments don't really make sense to me in the context of my knowledge
> > of the GIC.
> >
> > Of course all the CP0 timer and performance counter interrupts are per-CPU
> > and routed directly to the corresponding CP0_Cause[IP7..IP2] bits.  We are
> > don't need to give them further consideration.
> >
> >
> > Here is the scenario you should consider:
> >
> >    o 16 CPU cores.
> >    o 1 GIC routing interrupts from external sources to the 16 CPUs.
> >    o 2 network controllers each with an interrupt line routed to the GIC.
> >
> > Q: What would the GIC "interrupts" property look like?
> >
> > Note that the GIC doesn't have a single "interrupt-parent", as it can route
> > interrupts to *all* 16 CPUs.
> >
> > I propose that the GIC have neither an "interrupt-parent", nor "interrupts".
> > The fact that it is an "mti,global-interrupt-controller", means that the
> > software drivers for the GIC already know how to route interrupts, and any
> > information the device tree could contain is redundant.
>
> Ok, I misunderstood your opposition to the binding.
>
> My intention for the "interrupt-parent" and "interrupts" property of
> the GIC was to express that GIC interrupts are routed to the CPU
> interrupt vectors and that a certain set of these vectors are
> available for use by the GIC.  I would agree that these are mostly
> redundant (obviously the GIC routes interrupts to CPU interrupt
> vecotrs) and that it is not the most accurate description of the
> GIC-CPU relationship (the CPU interrupt controller are per-CPU, not
> global, and the GIC can route interrupts to any of them), though I'm
> not sure that there's a better way of describing it in DT.
>
> So that leaves us with something like this:
>
> interrupt-controller@1bdc0000 {
>          compatible = "mti,global-interrupt-controller";
>
>          interrupt-controller;
>          #interrupt-cells = <2>;
>
>          available-cpu-vectors = <2>, <3>, ...


Exactly what I had in mind, except for the missing "reg" property.

This gives software the information it needs, but doesn't impose any policy.

I will defer to others on the exact name the "available-cpu-vectors" 
should have.




> };
>
> DT folks, thoughts?

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