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

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Date:   Tue, 06 Nov 2018 15:45:54 -0800 (PST)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Christoph Hellwig <hch@...radead.org>, vincentc@...estech.com,
        aou@...s.berkeley.edu, alankao@...estech.com,
        greentime@...estech.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 Mon, 05 Nov 2018 00:52:52 PST (-0800), Arnd Bergmann wrote:
> 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.

Yes.  I don't want anything that won't compile with upstream GCC, but I also 
don't want to have a Kconfig that says "make the kernel only work on $VENDOR's 
implementation".  I think this can be achieved, at least for the cases I've 
seen so far.