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

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Date:   Tue, 30 Nov 2021 13:59:46 +0000
From:   Jessica Clarke <jrtc27@...c27.com>
To:     Heiko Stübner <heiko@...ech.de>
Cc:     linux-riscv <linux-riscv@...ts.infradead.org>,
        Wei Fu <wefu@...hat.com>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        taiten.peng@...onical.com, aniket.ponkshe@...onical.com,
        gordan.markus@...onical.com, Guo Ren <guoren@...ux.alibaba.com>,
        arnd@...db.de, wens@...e.org, maxime@...no.tech,
        Dan Lustig <dlustig@...dia.com>,
        Greg Favor <gfavor@...tanamicro.com>,
        andrea.mondelli@...wei.com, behrensj@....edu, xinhaoqu@...wei.com,
        huffman@...ence.com, Nick Kossifidis <mick@....forth.gr>,
        Allen Baum <allen.baum@...erantotech.com>,
        jscheid@...tanamicro.com, rtrauben@...il.com,
        Anup Patel <anup@...infault.org>,
        Rob Herring <robh+dt@...nel.org>,
        Anup Patel <anup.patel@....com>, atishp04@...il.com,
        Palmer Dabbelt <palmer@...belt.com>,
        Guo Ren <guoren@...nel.org>,
        Christoph Müllner <christoph.muellner@...ll.eu>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>, hch@....de,
        liush@...winnertech.com, Wei Wu <lazyparser@...il.com>,
        drew@...gleboard.org,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
Subject: Re: [PATCH V4 1/2] dt-bindings: riscv: add MMU Standard Extensions
 support for Svpbmt

On 30 Nov 2021, at 13:27, Heiko Stübner <heiko@...ech.de> wrote:
> 
> Hi,
> 
> Am Dienstag, 30. November 2021, 14:17:41 CET schrieb Jessica Clarke:
>> On 30 Nov 2021, at 12:07, Heiko Stübner <heiko@...ech.de> 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@...hat.com wrote:
>>>>>> From: Wei Fu <wefu@...hat.com>
>>>>>> 
>>>>>> 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@...hat.com>
>>>>>> Co-developed-by: Guo Ren <guoren@...nel.org>
>>>>>> Signed-off-by: Guo Ren <guoren@...nel.org>
>>>>>> Cc: Anup Patel <anup@...infault.org>
>>>>>> Cc: Palmer Dabbelt <palmer@...belt.com>
>>>>>> Cc: Rob Herring <robh+dt@...nel.org>
>>>>>> ---
>>>>>> 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@mail.gmail.com/
>>> 
>>> 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.
> 
> Heinrich asked how the other extensions should be handled
> (Svnapot, Svpbmt, Svinval), so what do you suggest to do with these?

Whatever is done for Zb[abcs], Zk*, Zv*, Zicbo*, etc. There may not be
a concrete plan for that yet, but that means you should speak with the
people involved with such extensions and come up with something
appropriate together.

Jess