Re: [PATCH 07/10] riscv: add ISA extension parsing for Zcmop

[Clément Léger]

On 11/04/2024 13:53, Conor Dooley wrote:
> On Thu, Apr 11, 2024 at 11:08:21AM +0200, Clément Léger wrote:
>>>> If we consider to have potentially broken isa string (ie extensions
>>>> dependencies not correctly handled), then we'll need some way to
>>>> validate this within the kernel.
>>>
>>> No, the DT passed to the kernel should be correct and we by and large we
>>> should not have to do validation of it. What I meant above was writing
>>> the binding so that something invalid will not pass dtbs_check.
>>
>> Acked, I was mainly answering Deepak question about dependencies wrt to
>> using __RISCV_ISA_EXT_SUPERSET() which does not seems to be relevant
>> since we expect a correct isa string to be passed.
> 
> Ahh, okay.
> 
>> But as you stated, DT
>> validation clearly make sense. I think a lot of extensions strings would
>> benefit such support (All the Zv* depends on V, etc).
> 
> I think it is actually as simple something like this, which makes it
> invalid to have "d" without "f":
> 
> | diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
> | index 468c646247aa..594828700cbe 100644
> | --- a/Documentation/devicetree/bindings/riscv/extensions.yaml
> | +++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
> | @@ -484,5 +484,20 @@ properties:
> |              Registers in the AX45MP datasheet.
> |              https://www.andestech.com/wp-content/uploads/AX45MP-1C-Rev.-5.0.0-Datasheet.pdf
> |  
> | +allOf:
> | +  - if:
> | +      properties:
> | +        riscv,isa-extensions:
> | +          contains:
> | +            const: "d"
> | +          not:
> | +            contains:
> | +              const: "f"
> | +    then:
> | +      properties:
> | +        riscv,isa-extensions:
> | +          false
> | +
> | +
> |  additionalProperties: true
> |  ...
> 
> If you do have d without f, the checker will say:
> cpu@2: riscv,isa-extensions: False schema does not allow ['i', 'm', 'a', 'd', 'c']
> 
> At least that's readable, even though not clear about what to do. I wish

That looks really readable indeed but the messages that result from
errors are not so informative.

It tried playing with various constructs and found this one to yield a
comprehensive message:

+allOf:
+  - if:
+      properties:
+        riscv,isa-extensions:
+          contains:
+            const: zcf
+          not:
+            contains:
+              const: zca
+    then:
+      properties:
+        riscv,isa-extensions:
+          items:
+            anyOf:
+              - const: zca

arch/riscv/boot/dts/allwinner/sun20i-d1-dongshan-nezha-stu.dtb: cpu@0:
riscv,isa-extensions:10: 'anyOf' conditional failed, one must be fixed:
        'zca' was expected
        from schema $id: http://devicetree.org/schemas/riscv/extensions.yaml

Even though dt-bindings-check passed, not sure if this is totally a
valid construct though...

Thanks,

Clément

> the former could be said about the wall of text you get for /each/
> undocumented entry in the string.