Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <CALs-Hssc6Uxf-6FKbye2n-CD0FWWE4xDmUWvN1NoKNFpn88SKg@mail.gmail.com>
 <mhng-ebe222a1-57eb-41cf-a541-38b4b5595ac0@palmer-ri-x1c9a>
In-Reply-To: <mhng-ebe222a1-57eb-41cf-a541-38b4b5595ac0@palmer-ri-x1c9a>
From:   Evan Green <evan@rivosinc.com>
Date:   Thu, 6 Jul 2023 14:08:42 -0700
Message-ID: <CALs-HstZRd1KMBkrn5D6jRs2CsaXXhk-OON=z-2YgnY8Ny60XA@mail.gmail.com>
Subject: Re: [PATCH v2] RISC-V: Show accurate per-hart isa in /proc/cpuinfo
To:     Palmer Dabbelt <palmer@dabbelt.com>
Cc:     Conor Dooley <conor.dooley@microchip.com>, ajones@ventanamicro.com,
        aou@eecs.berkeley.edu, apatel@ventanamicro.com,
        heiko.stuebner@vrull.eu, Paul Walmsley <paul.walmsley@sifive.com>,
        sunilvl@ventanamicro.com, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, Jul 6, 2023 at 12:45=E2=80=AFPM Palmer Dabbelt <palmer@dabbelt.com>=
 wrote:
>
> On Thu, 06 Jul 2023 12:34:30 PDT (-0700), Evan Green wrote:
> > On Thu, Jul 6, 2023 at 3:53=E2=80=AFAM Conor Dooley <conor.dooley@micro=
chip.com> wrote:
> >>
> >> On Thu, Jul 06, 2023 at 10:01:31AM +0200, Andrew Jones wrote:
> >> > On Wed, Jul 05, 2023 at 10:29:31AM -0700, Evan Green wrote:
> >> > > In /proc/cpuinfo, most of the information we show for each process=
or is
> >> > > specific to that hart: marchid, mvendorid, mimpid, processor, hart=
,
> >> > > compatible, and the mmu size. But the ISA string gets filtered thr=
ough a
> >> > > lowest common denominator mask, so that if one CPU is missing an I=
SA
> >> > > extension, no CPUs will show it.
> >> > >
> >> > > Now that we track the ISA extensions for each hart, let's report I=
SA
> >> > > extension info accurately per-hart in /proc/cpuinfo. We cannot cha=
nge
> >> > > the "isa:" line, as usermode may be relying on that line to show o=
nly
> >> > > the common set of extensions supported across all harts. Add a new=
 "hart
> >> > > isa" line instead, which reports the true set of extensions for th=
at
> >> > > hart. This matches what is returned in riscv_hwprobe() when queryi=
ng a
> >> > > given hart.
> >> > >
> >> > > Signed-off-by: Evan Green <evan@rivosinc.com>
> >> > >
> >> > > ---
> >> > >
> >> > > Changes in v2:
> >> > >  - Added new "hart isa" line rather than altering behavior of exis=
ting
> >> > >    "isa" line (Conor, Palmer)
> >> > >
> >> > >
> >> > > I based this series on top of Conor's riscv-extensions-strings bra=
nch
> >> > > from July 3rd, since otherwise this change gets hopelessly entangl=
ed
> >> > > with that series.
> >> > >
> >> > > I was unsure if I could snuggle the new "hart isa" line in just be=
low
> >> > > "isa". Aesthetically it would be quite pleasing, but it runs the r=
isk of
> >> > > breaking brittle usermode parsers that are assuming a specific lin=
e
> >> > > order. So I put it at the end.
> >> >
> >> > Actually, they're probably only aesthetically pleasing when they mat=
ch. If
> >> > there are differences, then I'd guess having them side by side, almo=
st the
> >> > same, but different, would make them even harder to look at then the=
y
> >> > already are. So I think I'll be happier with them separated by a few=
 lines
> >> > anyway.
> >>
> >> This list is eventually going to be so big that I don't think doing
> >> by-eye anything is going to be useful, so aesthetics be damned.
> >> That said, a parser that relies on the order of individual lines like
> >> that might deserve to be broken ;)
> >>
> >> Anyway, change looks good to me:
> >> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> >>
> >> I was thinking the uabi doc might need an update - should we add to it
> >> that "isa" means the common set & "hart isa"?
> >
> > I did do a little search for documentation to update, but failed to
> > come up with any. Which doc are you thinking of?
>
> Should be somewhere like Documentation/arch/riscv/uabi.rst

Thanks, I'll spin this patch and add something here.
-Evan