Re: [PATCH 1/2] dt-bindings: riscv: sifive-l2: add a PolarFire SoC compatible

[Heinrich Schuchardt <heinrich.schuchardt@canonical.com>]

On 8/25/22 20:56, Conor.Dooley@microchip.com wrote:
> On 25/08/2022 19:36, Heinrich Schuchardt wrote:
>> On 8/25/22 20:04, Conor Dooley wrote:
>>> From: Conor Dooley <conor.dooley@microchip.com>
>>>
>>> The l2 cache on PolarFire SoC is cross between that of the fu540 and
>>> the fu740. It has the extra interrupt from the fu740 but the lower
>>> number of cache-sets. Add a specific compatible to avoid the likes
>>> of:
>>>
>>> mpfs-polarberry.dtb: cache-controller@2010000: interrupts: [[1], [3], [4], [2]] is too long
>>
>> Where is such a message written? I couldn't find the string in
>> next-20220825 (git grep -n 'is too long"').
> 
> dtbs_check on next-20220825 (with dt-schema v22.08 FWIW):
> mpfs-polarberry.dtb: cache-controller@2010000: interrupts: [[1], [3], [4], [2]] is too long
> mpfs-icicle-kit.dtb: cache-controller@2010000: interrupts: [[1], [3], [4], [2]] is too long
> 
> I should have caught this before applying, but I got distracted
> by the unusable system.
> 
>>
>> Why should a different number of cache sets require an extra
>> compatible string. cache-size is simply a parameter going with> the existing compatible strings.
> 
> s/cache sets/interrupts
> Because the correct value for the fu540 is 3 & this is regulated by
> the binding. The alternative would be relaxing the binding to not
> regulate the number of interrupts.
> 
>>
>> I would assume that you only need an extra compatible string if
>> there is a functional difference that can not be expressed with
>> the existing parameters.
>>
>>>
>>> Fixes: 34fc9cc3aebe ("riscv: dts: microchip: correct L2 cache interrupts")
>>> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
>>> ---
>>>    .../bindings/riscv/sifive-l2-cache.yaml       | 79 ++++++++++++-------
>>>    1 file changed, 49 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/riscv/sifive-l2-cache.yaml b/Documentation/devicetree/bindings/riscv/sifive-l2-cache.yaml
>>> index 69cdab18d629..ca3b9be58058 100644
>>> --- a/Documentation/devicetree/bindings/riscv/sifive-l2-cache.yaml
>>> +++ b/Documentation/devicetree/bindings/riscv/sifive-l2-cache.yaml
>>> @@ -17,9 +17,6 @@ description:
>>>      acts as directory-based coherency manager.
>>>      All the properties in ePAPR/DeviceTree specification applies for this platform.
>>>    -allOf:
>>> -  - $ref: /schemas/cache-controller.yaml#
>>> -
>>>    select:
>>>      properties:
>>>        compatible:
>>> @@ -33,11 +30,16 @@ select:
>>>      properties:
>>>      compatible:
>>> -    items:
>>> -      - enum:
>>> -          - sifive,fu540-c000-ccache
>>> -          - sifive,fu740-c000-ccache
>>
>> Why can't you simply add microchip,mpfs-ccache here?
> 
> I *could* but I opted not to because the fu540 supports a compatible
> subset of the features & keeping the compatible for it allows systems
> with a newer dts to work with an older kernel.

That makes it clearer.

> 
>>
>>> -      - const: cache
>>> +    oneOf:
>>> +      - items:
>>> +          - enum:
>>> +              - sifive,fu540-c000-ccache
>>> +              - sifive,fu740-c000-ccache
>>> +          - const: cache
>>> +      - items:
>>> +          - const: microchip,mpfs-ccache
>>> +          - const: sifive,fu540-c000-ccache
>>
>> Why do we need 'sifive,fu540-c000-ccache' twice?
> 
> Is there a better way to write it given the above caveat?
> 
> Thanks,
> Conor.
> 
> 
>>
>>> +          - const: cache
>>>        cache-block-size:
>>>        const: 64
>>> @@ -72,29 +74,46 @@ properties:
>>>          The reference to the reserved-memory for the L2 Loosely Integrated Memory region.
>>>          The reserved memory node should be defined as per the bindings in reserved-memory.txt.
>>>    -if:
>>> -  properties:
>>> -    compatible:
>>> -      contains:
>>> -        const: sifive,fu540-c000-ccache
>>> +allOf:
>>> +  - $ref: /schemas/cache-controller.yaml#
>>>    -then:
>>> -  properties:
>>> -    interrupts:
>>> -      description: |
>>> -        Must contain entries for DirError, DataError and DataFail signals.
>>> -      maxItems: 3
>>> -    cache-sets:
>>> -      const: 1024
>>> -
>>> -else:
>>> -  properties:
>>> -    interrupts:
>>> -      description: |
>>> -        Must contain entries for DirError, DataError, DataFail, DirFail signals.
>>> -      minItems: 4
>>> -    cache-sets:
>>> -      const: 2048
>>> +  - if:
>>> +      properties:
>>> +        compatible:
>>> +          contains:
>>> +            enum:
>>> +              - sifive,fu740-c000-ccache
>>> +              - microchip,mpfs-ccache
>>> +
>>> +    then:
>>> +      properties:
>>> +        interrupts:
>>> +          description: |
>>> +            Must contain entries for DirError, DataError, DataFail, DirFail signals.
>>> +          minItems: 4

Above you indicated that you want strict limits for the interrupt count. 
You expect exactly 4 items here. Having 5 entries would not be correct.
Please, add 'maxItems: 4'.

>>> +
>>> +    else:
>>> +      properties:
>>> +        interrupts:
>>> +          description: |
>>> +            Must contain entries for DirError, DataError and DataFail signals.
>>> +          maxItems: 3

The item count should be exactly 3. Having 2 entries would not be correct.
Please, add 'minItems: 3'.

Best regards

Heinrich

>>> +
>>> +  - if:
>>> +      properties:
>>> +        compatible:
>>> +          contains:
>>> +            const: sifive,fu740-c000-ccache
>>> +
>>> +    then:
>>> +      properties:
>>> +        cache-sets:
>>> +          const: 2048
>>> +
>>> +    else:
>>> +      properties:
>>> +        cache-sets:
>>> +          const: 1024
>>>      additionalProperties: false
>>>