linux-kernel - Re: [PATCH] riscv: Work to remove kernel dependence on the M-extension

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Message-ID: <YimxItxjPsPTXeub@infradead.org>
Date:   Thu, 10 Mar 2022 00:04:50 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Christoph Hellwig <hch@...radead.org>, michael@...haelkloos.com,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Work to remove kernel dependence on the
 M-extension

On Wed, Mar 09, 2022 at 11:34:25PM -0800, Palmer Dabbelt wrote:
> If someone has hardware that lacks M and users care about running Linux on
> that then I'm happy to support it.  I'll still point out the silliness of
> that decision, but if it's too late to change things then I'd rather support
> the hardware.  If it's one of these "fill out every possible allowed ISA
> flavor, even if nobody has one that runs Linux" then I don't see a reason to
> bother -- there's an infinite amount of allowable RISC-V implementations,
> we'll all go crazy chasing them around.

It's not like Linux had required M mode since the RISC-V port was merged
upstream, so any new implementor really should know about it.  And
performance on anything that requires Linux will just be horrible.
I could see a bit of an excuse for a nommu port.

Anyway, this kind of patch really does need to state the why.  And it
better be a really good reason.