linux-kernel - Re: [PATCH v1 3/9] RISC-V: shunt isa_ext

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Date:   Mon, 26 Jun 2023 16:59:25 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Andrew Jones <ajones@...tanamicro.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>,
        Heiko Stuebner <heiko.stuebner@...ll.eu>,
        Evan Green <evan@...osinc.com>,
        Sunil V L <sunilvl@...tanamicro.com>,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/9] RISC-V: shunt isa_ext_arr to cpufeature.c

On Mon, Jun 26, 2023 at 05:44:18PM +0200, Andrew Jones wrote:
> On Mon, Jun 26, 2023 at 05:29:04PM +0200, Andrew Jones wrote:
> > On Mon, Jun 26, 2023 at 12:19:41PM +0100, Conor Dooley wrote:
> ...
> > > +const struct riscv_isa_ext_data riscv_isa_ext[] = {
> > > +	__RISCV_ISA_EXT_DATA(zicbom, RISCV_ISA_EXT_ZICBOM),
> > > +	__RISCV_ISA_EXT_DATA(zicboz, RISCV_ISA_EXT_ZICBOZ),
> > > +	__RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
> > > +	__RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),
> > > +	__RISCV_ISA_EXT_DATA(zifencei, RISCV_ISA_EXT_ZIFENCEI),
> > > +	__RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
> > > +	__RISCV_ISA_EXT_DATA(zihpm, RISCV_ISA_EXT_ZIHPM),
> > > +	__RISCV_ISA_EXT_DATA(zba, RISCV_ISA_EXT_ZBA),
> > > +	__RISCV_ISA_EXT_DATA(zbb, RISCV_ISA_EXT_ZBB),
> > > +	__RISCV_ISA_EXT_DATA(zbs, RISCV_ISA_EXT_ZBS),
> > > +	__RISCV_ISA_EXT_DATA(smaia, RISCV_ISA_EXT_SMAIA),
> > > +	__RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
> > > +	__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),
> > > +	__RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
> > > +	__RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> > > +	__RISCV_ISA_EXT_DATA("", RISCV_ISA_EXT_MAX),
> > 
> > I think we can either drop this null entry or drop the count variable
> > below. My preference would be to drop the count variable, and always
> > loop to the null.
> 
> Eh, never mind, the entry isn't null, it's "". Why do we have that entry
> though? I guess it can be dropped?

It may just be cargo culting? The commit that added this, a9b202606c69
("RISC-V: Improve /proc/cpuinfo output for ISA extensions") [1], added
an empty array other than this element & perhaps it was just not removed
when real entries were added? Symptom of adding a feature without an
actual user (multiletter extension) perhaps?

1 - https://lore.kernel.org/all/20220314203845.832648-1-atishp@rivosinc.com/

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