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

[Hector Martin]

On 10/03/2021 01.11, Rob Herring wrote:
> 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.

This makes sense. Since we aren't using the sec-hyp stuff here, and 
those go at the end of the list, we can omit them from this patch for 
now and add them whenever they're needed for a platform. Does that sound OK?

-- 
Hector Martin (marcan at marcan.st)
Public Key: https://mrcn.st/pub