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 16:01:47 +0100
From:   Philipp Tomsich <philipp.tomsich@...ll.eu>
To:     Jessica Clarke <jrtc27@...c27.com>
Cc:     Heiko Stübner <heiko@...ech.de>,
        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>,
        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

We did touch on this in our coordination call a few weeks ago: the
grouping under mmu and the bool-entries were chosen because of their
similarity to other extensions (i.e. for Zb[abcs] there could/should
be a bool-entry under each cpu-node — for some Zv* entries a subnode
might be needed with further parameters).

The string-based approach (as in the originally proposed "mmu-type=")
would like not scale with the proliferation of small & modular
extensions.

Philipp.


On Tue, 30 Nov 2021 at 14:59, Jessica Clarke <jrtc27@...c27.com> wrote:
>
> 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
>