linux-kernel - Re: [RESEND PATCH V3 1/2] dt-bindings: riscv: add mmu-supports-svpbmt for Svpbmt

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Date:   Mon, 25 Oct 2021 14:00:46 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Anup Patel <anup@...infault.org>
Cc:     Wei Fu <wefu@...hat.com>, Anup Patel <anup.patel@....com>,
        Atish Patra <atish.patra@....com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Christoph Müllner <christoph.muellner@...ll.eu>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Christoph Hellwig <hch@....de>,
        liush <liush@...winnertech.com>,
        Wei Wu (吴伟) <lazyparser@...il.com>,
        Drew Fustini <drew@...gleboard.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        taiten.peng@...onical.com,
        Aniket Ponkshe <aniket.ponkshe@...onical.com>,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Gordan Markus <gordan.markus@...onical.com>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Arnd Bergmann <arnd@...db.de>, Chen-Yu Tsai <wens@...e.org>,
        Maxime Ripard <maxime@...no.tech>,
        Daniel Lustig <dlustig@...dia.com>,
        Greg Favor <gfavor@...tanamicro.com>,
        Andrea Mondelli <andrea.mondelli@...wei.com>,
        Jonathan Behrens <behrensj@....edu>,
        Xinhaoqu <xinhaoqu@...wei.com>,
        Bill Huffman <huffman@...ence.com>,
        Nick Kossifidis <mick@....forth.gr>,
        Allen Baum <allen.baum@...erantotech.com>,
        Josh Scheid <jscheid@...tanamicro.com>,
        Richard Trauben <rtrauben@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [RESEND PATCH V3 1/2] dt-bindings: riscv: add mmu-supports-svpbmt
 for Svpbmt

On Mon, Oct 25, 2021 at 12:17 PM Anup Patel <anup@...infault.org> wrote:
>
> On Mon, Oct 25, 2021 at 9:36 AM <wefu@...hat.com> wrote:
> >
> > From: Wei Fu <wefu@...hat.com>
> >
> > Previous patch has added svpbmt in arch/riscv and changed the
> > DT mmu-type. 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 | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > index e534f6a7cfa1..76f324d85e12 100644
> > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > @@ -59,6 +59,11 @@ properties:
> >        - riscv,sv48
> >        - riscv,none
> >
> > +  mmu-supports-svpbmt:
> > +    description:
> > +      Describes the CPU's mmu-supports-svpbmt support
> > +    $ref: '/schemas/types.yaml#/definitions/phandle'
>
> There were various proposals from different folks in the previous
> email threads.
>
> I think most of us were converging on:
> 1) Don't modify "mmu-type" DT property for backward
> compatibility
I agree. FuWei has followed that in the patch.

> 2) Add boolean DT property "riscv,svpmbt" under
> "mmu" child DT node of each CPU DT node. Same will apply
> to boolean DT property "riscv,svnapot" as well.
We have various proposals here:
@Philipp suggests firstly, but break the backward compatibility:
 cpu@0 {
    ...
    mmu {
       type = "riscv,sv39";
       supports-svpbmt;
       supports-svnapot;
    };

@guoren suggests reusing the mmu-type, but seems not clean.
cpu@0 {
   ...
   mmu-type = "riscv,sv39,svpbmt,svnapot";


@fuwei suggests simple name property in CPU section:
cpu@0 {
   ...
   mmu-type = "riscv,sv39";
   mmu-supports-svpbmt;
   mmu-supports-svnapot;

@Anup suggests:
cpu@0 {
   ...
    mmu-type = "riscv,sv39";
    mmu {
       supports-svpbmt;
       supports-svnapot;
    };

Any other suggestions? Thx.

>
> We also have bitmanip and vector broken down into smaller
> extensions so grouping related extensions as separate DT node
> under each CPU node will be more readable and easy to parse.
Do you mean combine mmu extensions with them together?
cpu@0 {
    ...
    extensions {
        supports-svpbmt;
        supports-svnapot;
        supports-bitmanip;
        supports-vector-v0p7;
    };

>
> Regards,
> Anup
>
> > +
> >    riscv,isa:
> >      description:
> >        Identifies the specific RISC-V instruction set architecture
> > --
> > 2.25.4
> >



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/