linux-kernel - Re: [PATCH] riscv: kbuild: drop CONFIG_RISCV_ISA

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Message-ID: <CAMabmM+YX3L-J1GCvDaC9H66YMArfs6PuKCsE_dNMBtApOxZig@mail.gmail.com>
Date:   Tue, 13 Aug 2019 00:18:22 +0200
From:   Charles Papon <charles.papon.90@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Bin Meng <bmeng.cn@...il.com>, Atish Patra <atish.patra@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH] riscv: kbuild: drop CONFIG_RISCV_ISA_C

> Because it it the unix platform baseline as stated in the patch.
I know that, but i'm looking for arguments why RVC could't be kept as
an option, especialy it is only an optimisation option without
behavioral/code changes.

That baseline make sense for heavy linux distributions, where you
expect everybody to compile with a baseline set of ISA extentions, to
make binary exchanges easier.
But for smaller systems, i do not see advantages having RVC forced.

On Mon, Aug 12, 2019 at 5:03 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Thu, Aug 08, 2019 at 02:18:53PM +0200, Charles Papon wrote:
> > Please do not drop it.
> >
> > Compressed instruction extension has some specific overhead in small
> > RISC-V FPGA softcore, especialy in the ones which can't implement the
> > register file read in a asynchronous manner because of the FPGA
> > technology.
> > What are reasons to enforce RVC ?
>
> Because it it the unix platform baseline as stated in the patch.