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

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Message-ID: <Y+KTwoYwqhFiDerT@spud>
Date:   Tue, 7 Feb 2023 18:09:06 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Anup Patel <apatel@...tanamicro.com>
Cc:     Palmer Dabbelt <palmer@...belt.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 Tue, Feb 07, 2023 at 06:05:11PM +0000, Conor Dooley wrote:
> Hey Anup, Palmer,
> 
> On Fri, Feb 03, 2023 at 05:31:01PM +0530, Anup Patel wrote:
> > On Fri, Feb 3, 2023 at 5:54 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.
> > >
> > > I just sent
> > > <https://lore.kernel.org/r/20230203001201.14770-1-palmer@rivosinc.com/>
> > > which documents that.
> > 
> > I am not sure why you say that these are custom extensions.
> > 
> > Multiple folks have clarified that both Smaia and Ssaia are frozen
> > ISA extensions as-per RVI process. The individual chapters which
> > are in the draft state have nothing to do with Smaia and Ssaia CSRs.
> > 
> > Please refer:
> > https://github.com/riscv/riscv-aia/pull/36
> > https://lists.riscv.org/g/tech-aia/message/336
> > https://lists.riscv.org/g/tech-aia/message/337
> 
> All of these links seem to discuss the draft chapters somehow being
> incompatible with the non-draft ones. I would very expect that that,
> as pointed out in several places there, that the draft chapters
> finalisation would not lead to meaningful (and incompatible!) changes
> being made to the non-draft chapters.
> 
> Maybe yourself and Palmer are looking at this from different
> perspectives? Looking at his patch from Friday:
> https://lore.kernel.org/linux-riscv/20230203001201.14770-1-palmer@rivosinc.com/
> He specifically mentioned this aspect, as opposed to the aspect that
> your links refer to.

Meh, bad re-ordering of my paragraphs. By "this aspect" I meant what is
in the below paragraph! Apologies for any confusion there :)

> Surely a duo-plic, if that ever comes to be, could be detected from
> compatible strings in DT or w/e - but how do you intend differentiating
> between an implementation of S*aia that contains the IOMMU support in
> Chapter 9 in a finalised form, versus an implementation that may make
> "different decisions" when it comes to that chapter of the spec?
> I thought that would be handled by extension versions, but I am told
> that those are not a thing any more.
> If that's not true, and there'll be a version number that we can pull in
> from a DT and parse which will distinguish between the two, then please
> correct my misunderstanding here!
> 
> Thanks,
> Conor.
> 
> > > > 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.
> > 
> > I am planning to send this series as a second PR for Linux-6.3 after your
> > PR (which includes ISA string refactoring) is merged. Is that okay with you?
> > 
> > With that said, it would request you to ACK this patch as well.
> > 
> > >
> > > >       __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
> > > >               }
> > 
> > Thanks,
> > Anup



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