Re: [PATCH V4 1/2] dt-bindings: riscv: add MMU Standard Extensions support for Svpbmt

[Jessica Clarke]

On 30 Nov 2021, at 12:07, Heiko Stübner <heiko@xxxxxxxxx> wrote:
> 
> Am Montag, 29. November 2021, 13:06:23 CET schrieb Heiko Stübner:
>> Am Montag, 29. November 2021, 09:54:39 CET schrieb Heinrich Schuchardt:
>>> On 11/29/21 02:40, wefu@xxxxxxxxxx wrote:
>>>> From: Wei Fu <wefu@xxxxxxxxxx>
>>>> 
>>>> Previous patch has added svpbmt in arch/riscv and add "riscv,svpmbt"
>>>> in the DT mmu node. Update dt-bindings related property here.
>>>> 
>>>> Signed-off-by: Wei Fu <wefu@xxxxxxxxxx>
>>>> Co-developed-by: Guo Ren <guoren@xxxxxxxxxx>
>>>> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
>>>> Cc: Anup Patel <anup@xxxxxxxxxxxxxx>
>>>> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
>>>> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
>>>> ---
>>>>  Documentation/devicetree/bindings/riscv/cpus.yaml | 10 ++++++++++
>>>>  1 file changed, 10 insertions(+)
>>>> 
>>>> diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
>>>> index aa5fb64d57eb..9ff9cbdd8a85 100644
>>>> --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
>>>> +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
>>>> @@ -63,6 +63,16 @@ properties:
>>>>        - riscv,sv48
>>>>        - riscv,none
>>>> 
>>>> +  mmu:
>>> 
>>> Shouldn't we keep the items be in alphabetic order, i.e. mmu before 
>>> mmu-type?
>>> 
>>>> +    description:
>>>> +      Describes the CPU's MMU Standard Extensions support.
>>>> +      These values originate from the RISC-V Privileged
>>>> +      Specification document, available from
>>>> +      https://riscv.org/specifications/
>>>> +    $ref: '/schemas/types.yaml#/definitions/string'
>>>> +    enum:
>>>> +      - riscv,svpmbt
>>> 
>>> The privileged specification has multiple MMU related extensions: 
>>> Svnapot, Svpbmt, Svinval. Shall they all be modeled in this enum?
>> 
>> I remember in some earlier version some way back there was the
>> suggestion of using a sub-node instead and then adding boolean
>> properties for the supported extensions.
>> 
>> Aka something like
>> 	mmu {
>> 		riscv,svpbmt;	
>> 	};
> 
> For the record, I'm talking about the mail from september
> https://lore.kernel.org/linux-riscv/CAAeLtUChjjzG+P8yg45GLZMJy5UR2K5RRBoLFVZhtOaZ5pPtEA@xxxxxxxxxxxxxx/
> 
> So having a sub-node would make adding future extensions
> way nicer.

Svpbmt is just an ISA extension, and should be treated like any other.
Let’s not invent two different ways of representing that in the device
tree.

Jess