On Thu, 05 Apr 2012 13:59:56 +0100, Marc Zyngier <[email protected]> wrote:
> On 03/04/12 16:35, Grant Likely wrote:
>
> Hi Grant,
>
> > On Tue, 03 Apr 2012 10:53:44 +0100, Marc Zyngier <[email protected]>
> > wrote:
> >> On 03/04/12 10:22, David Vrabel wrote:
> >>
> >> Hi David,
> >>
> >>> On 02/04/12 17:30, Marc Zyngier wrote:
> >>>> The GICv2 can have virtualization extension support, consisting
> >>>> of an additional set of registers and interrupts. Add the necessary
> >>>> binding to the GIC DT documentation.
> >>>
> >>> The Xen hypervisor's device tree support is very much incomplete so I've
> >>> not looked into this is much detail.
> >>>
> >>> Would it make more sense to extend the existing gic binding with the the
> >>> additional information rather than adding a new node?
> >>
> >> I'm actually torn between the two approaches. On one side, the VGIC is
> >> part of the GIC spec, hence should be part of the GIC node. On the other
> >> hand, it is logically handled by a different piece of software (the
> >> hypervisor), and would normally be probed separately. Having a separate
> >> node makes the probing more sensible.
> >
> > Don't get too hung up on the software side of things. Describe it in
> > a way that makes sense for the hardware. There is lots of precidence
> > for two hunks of software initializating from the same node; either by
> > probe kicking off two init hooks, or by early init code going looking
> > for the node manually.
>
> What I'm trying to avoid is a royal mess in the future if we get some
> other extension to the GIC.
>
> Let's say we implement the following:
>
> gic: interrupt-controller@2c001000 {
> compatible = "arm,cortex-a15-gic";
> #interrupt-cells = <3>;
> #address-cells = <1>;
> interrupt-controller;
> reg = <0x2c001000 0x1000>,
> <0x2c002000 0x100>,
> <0x2c004000 0x2000>,
> <0x2c006000 0x2000>;
> interrupts = <1 9 0xf04>;
> };
>
> It's all fine (the two last regions and the interrupt are for VGIC),
> until someone comes up with extension FOO which requires two new regions
> and am interrupt. It is then impossible to distinguish between the two,
> short of adding more attributes.
>
> How about this?
>
> gic: interrupt-controller@2c001000 {
> compatible = "arm,cortex-a15-gic";
> #interrupt-cells = <3>;
> #address-cells = <1>;
> #size-cells = <1>;
> interrupt-controller;
> reg = <0x2c001000 0x1000>,
> <0x2c002000 0x100>;
>
> vgic@2c004000 {
> compatible = "arm,cortex-a15-vgic", "arm,vgic";
> reg = <0x2c004000 0x2000>,
> <0x2c006000 0x2000>;
> interrupts = <1 9 0xf04>;
> };
> };
>
> It cleanly separate the extension from the core GIC, and still make it
> part of the GIC node.
I think that the compatible property already supports what you need to
do. If an extension is added to the core binding, then suppliment it
with a new compatible value:
gic: interrupt-controller@2c001000 {
compatible = "arm,cortex-a15-vgic", "arm,cortex-a15-gic";
#interrupt-cells = <3>;
#address-cells = <1>;
#size-cells = <1>;
interrupt-controller;
reg = <0x2c001000 0x1000>,
<0x2c002000 0x100>,
<0x2c004000 0x2000>,
<0x2c006000 0x2000>;
interrupts = <1 9 0xf04>;
};
Or, if it can be done in a backwards compatible way, then just extend
the existing binding. In you're example above, the 'vgic' extension
only gets enabled if the 3rd and 4th 'reg' tuples are added.
g.
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