[RFT PATCH v3 06/27] dt-bindings: timer: arm,arch_timer: Add interrupt-names support

[Rob Herring]

On Mon, Mar 8, 2021 at 3:42 PM Marc Zyngier <maz at kernel.org> wrote:
>
> On Mon, 08 Mar 2021 20:38:41 +0000,
> Rob Herring <robh at kernel.org> wrote:
> >
> > On Fri, Mar 05, 2021 at 06:38:41AM +0900, Hector Martin wrote:
> > > Not all platforms provide the same set of timers/interrupts, and Linux
> > > only needs one (plus kvm/guest ones); some platforms are working around
> > > this by using dummy fake interrupts. Implementing interrupt-names allows
> > > the devicetree to specify an arbitrary set of available interrupts, so
> > > the timer code can pick the right one.
> > >
> > > This also adds the hyp-virt timer/interrupt, which was previously not
> > > expressed in the fixed 4-interrupt form.
> > >
> > > Signed-off-by: Hector Martin <marcan at marcan.st>
> > > ---
> > >  .../devicetree/bindings/timer/arm,arch_timer.yaml  | 14 ++++++++++++++
> > >  1 file changed, 14 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml b/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml
> > > index 2c75105c1398..ebe9b0bebe41 100644
> > > --- a/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml
> > > +++ b/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml
> > > @@ -34,11 +34,25 @@ properties:
> > >                - arm,armv8-timer
> > >
> > >    interrupts:
> > > +    minItems: 1
> > > +    maxItems: 5
> > >      items:
> > >        - description: secure timer irq
> > >        - description: non-secure timer irq
> > >        - description: virtual timer irq
> > >        - description: hypervisor timer irq
> > > +      - description: hypervisor virtual timer irq
> > > +
> > > +  interrupt-names:
> > > +    minItems: 1
> > > +    maxItems: 5
> > > +    items:
> > > +      enum:
> > > +        - phys-secure
> > > +        - phys
> > > +        - virt
> > > +        - hyp-phys
> > > +        - hyp-virt
> >
> > phys-secure and hyp-phys is not very consistent. secure-phys or sec-phys
> > instead?
> >
> > This allows any order which is not ideal (unfortunately json-schema
> > doesn't have a way to define order with optional entries in the middle).
> > How many possible combinations are there which make sense? If that's a
> > reasonable number, I'd rather see them listed out.
>
> The available of interrupts are a function of the number of security
> states, privileged exception levels and architecture revisions, as
> described in D11.1.1:
>
> <quote>
> - An EL1 physical timer.
> - A Non-secure EL2 physical timer.
> - An EL3 physical timer.
> - An EL1 virtual timer.
> - A Non-secure EL2 virtual timer.
> - A Secure EL2 virtual timer.
> - A Secure EL2 physical timer.
> </quote>
>
> * Single security state, EL1 only, ARMv7 & ARMv8.0+ (assumed NS):
>   - physical, virtual
>
> * Single security state, EL1 + EL2, ARMv7 & ARMv8.0 (assumed NS)
>   - physical, virtual, hyp physical
>
> * Single security state, EL1 + EL2, ARMv8.1+ (assumed NS)
>   - physical, virtual, hyp physical, hyp virtual
>
> * Two security states, EL1 + EL3, ARMv7 & ARMv8.0+:
>   - secure physical, physical, virtual
>
> * Two security states, EL1 + EL2 + EL3, ARMv7 & ARMv8.0
>   - secure physical, physical, virtual, hyp physical
>
> * Two security states, EL1 + EL2 + EL3, ARMv8.1+
>   - secure physical, physical, virtual, hyp physical, hyp virtual
>
> * Two security states, EL1 + EL2 + S-EL2 + EL3, ARMv8.4+
>   - secure physical, physical, virtual, hyp physical, hyp virtual,
>     secure hyp physical, secure hyp virtual
>
> Nobody has seen the last combination in the wild (that is, outside of
> a SW model).
>
> I'm really not convinced we want to express this kind of complexity in
> the binding (each of the 7 cases), specially given that we don't
> encode the underlying HW architecture level or number of exception
> levels anywhere, and have ho way to validate such information.

Actually, we can simplify this down to 2 cases:

oneOf:
  - minItems: 2
    items:
      - const: phys
      - const: virt
      - const: hyp-phys
      - const: hyp-virt
  - minItems: 3
    items:
      - const: sec-phys
      - const: phys
      - const: virt
      - const: hyp-phys
      - const: hyp-virt
      - const: sec-hyp-phy
      - const: sec-hyp-virt

And that's below my threshold for not worth the complexity.

Rob