linux-kernel - Re: [PATCH v2 2/7] RISC-V: Detect AIA CSRs from ISA string

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Message-ID: <CAEg0e7hrQFu+cdZy+3QO1ML9FNTPBehZwOOBnr1F-5ABYDnkGg@mail.gmail.com>
Date:   Wed, 15 Feb 2023 16:41:29 +0100
From:   Christoph Müllner <christoph.muellner@...ll.eu>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     apatel@...tanamicro.com, pbonzini@...hat.com,
        atishp@...shpatra.org, Paul Walmsley <paul.walmsley@...ive.com>,
        ajones@...tanamicro.com, anup@...infault.org, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/7] RISC-V: Detect AIA CSRs from ISA string

On Fri, Feb 3, 2023 at 1:25 AM Palmer Dabbelt <palmer@...belt.com> wrote:
>
> On Fri, 27 Jan 2023 23:27:32 PST (-0800), apatel@...tanamicro.com wrote:
> > We have two extension names for AIA ISA support: Smaia (M-mode AIA CSRs)
> > and Ssaia (S-mode AIA CSRs).
>
> This has pretty much the same problem that we had with the other
> AIA-related ISA string patches, where there's that ambiguity with the
> non-ratified chapters.  IIRC when this came up in GCC the rough idea was
> to try and document that we're going to interpret the standard ISA
> strings that way, but now that we're doing custom ISA extensions it
> seems saner to just define on here that removes the ambiguity.

To avoid the impression that I did not work on that, here is the v2
from November,
that attempts to document this:
  https://gcc.gnu.org/pipermail/gcc-patches/2022-November/607326.html

My proposed text was:
+Note, that AIA support (@samp{Smaia} and @samp{Ssaia}) is based on an AIA
+specification, which is frozen but contains draft chapters ("Duo-PLIC" and
+"IOMMU Support").

Btw, I did not get any feedback on that patch.

I also tried to address this on spec level (the PR has been linked) and raised
that to tech-aia (the conversation has been linked).

Another thing that I want to highlight, since it was discussed a lot recently
(e.g. just a few minutes ago in tech-chairs).
There is a chance of a last-minute spec change of AIA:
  https://github.com/riscv/riscv-aia/pull/37

BR
Christoph

>
>
> I just sent
> <https://lore.kernel.org/r/20230203001201.14770-1-palmer@rivosinc.com/>
> which documents that.
>
> > We extend the ISA string parsing to detect Smaia and Ssaia extensions.
> >
> > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
> > ---
> >  arch/riscv/include/asm/hwcap.h | 2 ++
> >  arch/riscv/kernel/cpu.c        | 2 ++
> >  arch/riscv/kernel/cpufeature.c | 2 ++
> >  3 files changed, 6 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index 86328e3acb02..341ef30a3718 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -59,6 +59,8 @@ enum riscv_isa_ext_id {
> >       RISCV_ISA_EXT_ZIHINTPAUSE,
> >       RISCV_ISA_EXT_SSTC,
> >       RISCV_ISA_EXT_SVINVAL,
> > +     RISCV_ISA_EXT_SMAIA,
> > +     RISCV_ISA_EXT_SSAIA,
> >       RISCV_ISA_EXT_ID_MAX
> >  };
> >  static_assert(RISCV_ISA_EXT_ID_MAX <= RISCV_ISA_EXT_MAX);
> > diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> > index 1b9a5a66e55a..a215ec929160 100644
> > --- a/arch/riscv/kernel/cpu.c
> > +++ b/arch/riscv/kernel/cpu.c
> > @@ -162,6 +162,8 @@ arch_initcall(riscv_cpuinfo_init);
> >   *    extensions by an underscore.
> >   */
> >  static struct riscv_isa_ext_data isa_ext_arr[] = {
> > +     __RISCV_ISA_EXT_DATA(smaia, RISCV_ISA_EXT_SMAIA),
> > +     __RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
>
> This will conflict with that ISA string refactoring I just merged.  It
> should be a pretty mechanical merge conflict, but if you want we can do
> a shared tag with the first few patches and I can handle the merge
> conflict locally.
>
> >       __RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
> >       __RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
> >       __RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 93e45560af30..3c5b51f519d5 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -228,6 +228,8 @@ void __init riscv_fill_hwcap(void)
> >                               SET_ISA_EXT_MAP("zihintpause", RISCV_ISA_EXT_ZIHINTPAUSE);
> >                               SET_ISA_EXT_MAP("sstc", RISCV_ISA_EXT_SSTC);
> >                               SET_ISA_EXT_MAP("svinval", RISCV_ISA_EXT_SVINVAL);
> > +                             SET_ISA_EXT_MAP("smaia", RISCV_ISA_EXT_SMAIA);
> > +                             SET_ISA_EXT_MAP("ssaia", RISCV_ISA_EXT_SSAIA);
> >                       }
> >  #undef SET_ISA_EXT_MAP
> >               }
>
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