linux-kernel - Re: [RFC 0/2] RISC-V: A proposal to add vendor-specific code

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Message-ID: <CAK8P3a2c98VVPArCkdAR=-nnDBq1gYRCLDDgQB71eGiTSRdb4A@mail.gmail.com>
Date:   Mon, 5 Nov 2018 09:52:52 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Vincent Chen <vincentc@...estech.com>, aou@...s.berkeley.edu,
        alankao@...estech.com, greentime@...estech.com, palmer@...ive.com,
        linux-kernel@...r.kernel.org, zong@...estech.com,
        kito@...estech.com, linux-riscv@...ts.infradead.org,
        deanbo422@...il.com
Subject: Re: [RFC 0/2] RISC-V: A proposal to add vendor-specific code

On 11/5/18, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, Nov 05, 2018 at 02:58:07PM +0800, Vincent Chen wrote:
>> Many thanks for kinds of comments. I quickly synthesize the comments and
>> list them as below.
>> 1. The kernel image shall include all vendor-specific code.
>
> I fundamentally disagree with this… and think it should be the contrary.
>
> 1. The kernel shall support no vendor specific instructions whatsoever,
> period.

I think what was meant above is

1. If a vendor extension requires kernel support, that support
must be able to be built into a kernel image without breaking support
for CPUs that do not have that extension, to allow building a single
kernel image that works on all CPUs.

       Arnd