linux-kernel - Re: [PATCH v1 6/9] RISC-V: add single letter extensions to riscv_isa

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Date:   Wed, 28 Jun 2023 18:43:15 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Evan Green <evan@...osinc.com>
Cc:     Conor Dooley <conor.dooley@...rochip.com>, palmer@...belt.com,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Jones <ajones@...tanamicro.com>,
        Heiko Stuebner <heiko.stuebner@...ll.eu>,
        Sunil V L <sunilvl@...tanamicro.com>,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 6/9] RISC-V: add single letter extensions to
 riscv_isa_ext

On Wed, Jun 28, 2023 at 10:33:20AM -0700, Evan Green wrote:
> On Mon, Jun 26, 2023 at 4:21 AM Conor Dooley <conor.dooley@...rochip.com> wrote:
> >
> > So that riscv_fill_hwcap() can use riscv_isa_ext to probe for single
> > letter extensions, add them to it. riscv_isa_ext_data grows a new
> > member, signifying whether an extension is multi-letter & thus requiring
> > special handling.
> > As a result, what gets spat out in /proc/cpuinfo will become borked, as
> > single letter extensions will be printed as part of the base extensions
> > and while printing from riscv_isa_arr. Take the opportunity to unify the
> > printing of the isa string, using the new member of riscv_isa_ext_data
> > in the process.
> >
> > Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> > ---
> >  arch/riscv/include/asm/hwcap.h |  1 +
> >  arch/riscv/kernel/cpu.c        | 36 ++++++----------------
> >  arch/riscv/kernel/cpufeature.c | 56 +++++++++++++++++++++-------------
> >  3 files changed, 46 insertions(+), 47 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index a35bee219dd7..6ad896dc4342 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -77,6 +77,7 @@ unsigned long riscv_get_elf_hwcap(void);
> >  struct riscv_isa_ext_data {
> >         const unsigned int id;
> >         const char *name;
> > +       const bool multi_letter;
> 
> Instead of defining a new member, could we just infer this by making a
> macro like #define MULTI_LETTER(name) (name[0] && name[1])?

Or don't even try to be clever like this and just call strnlen on the
name & check if it is 1? It's only used in 2 places.

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