linux-kernel - Re: [PATCH] riscv: Add RISC-V svpbmt extension

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Date:   Thu, 23 Sep 2021 12:42:28 +0300
From:   Nick Kossifidis <mick@....forth.gr>
To:     Anup Patel <anup@...infault.org>
Cc:     Nick Kossifidis <mick@....forth.gr>, Guo Ren <guoren@...nel.org>,
        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>, wefu@...hat.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@...onical.com,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        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>,
        Allen Baum <allen.baum@...erantotech.com>,
        Josh Scheid <jscheid@...tanamicro.com>,
        Richard Trauben <rtrauben@...il.com>
Subject: Re: [PATCH] riscv: Add RISC-V svpbmt extension

Στις 2021-09-23 12:37, Anup Patel έγραψε:
> On Thu, Sep 23, 2021 at 2:55 PM Nick Kossifidis <mick@....forth.gr> 
> wrote:
>> 
>> Hello Guo,
>> 
>> Στις 2021-09-23 10:27, guoren@...nel.org έγραψε:
>> diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml
>> b/Documentation/devicetree/bindings/riscv/cpus.yaml
>> index e534f6a7cfa1..1825cd8db0de 100644
>> --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
>> +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
>> @@ -56,7 +56,9 @@ properties:
>>       enum:
>>         - riscv,sv32
>>         - riscv,sv39
>> +      - riscv,sv39,svpbmt
>>         - riscv,sv48
>> +      - riscv,sv48,svpbmt
>>         - riscv,none
>> 
>> Isn't svpbmt orthogonal to the mmu type ? It's a functionality that 
>> can
>> be present on either sv39/48/57 so why not have another "svpbmt"
>> property directly on the cpu node ?
> 
> Actually, "mmu-type" would be a good place because it's page based
> memory attribute and paging can't exist without mmu translation mode.
> 
> Also, "svpmbt" is indeed a CPU property so has to be feature individual
> CPU node. Hypothetically, a heterogeneous system is possible where
> some CPUs have "svpmbt" and some CPUs don't have "svpmbt". For
> example, a future FUxxx SoC might have a E-core and few S-cores
> where S-cores have Svpmbt whereas E-core does not have Svpmbt
> because it's an embedded core.
> 

I should say cpuX node, not the root /cpu node. We can have an svpbmt 
property in the same way we have an mmu-type property.

Regards,
Nick