Re: [PATCH] riscv: deprecate CONFIG_MMU=n

From: "Clément Léger" <cleger@rivosinc.com>
To: Charles Lohr <lohr85@gmail.com>, Conor Dooley <conor@kernel.org>
Cc: "Samuel Holland" <samuel.holland@sifive.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	"Conor Dooley" <conor.dooley@microchip.com>,
	"Andrew Jones" <ajones@ventanamicro.com>,
	"Damien Le Moal" <dlemoal@kernel.org>,
	"Björn Töpel" <bjorn@rivosinc.com>,
	"Atish Patra" <atishp@rivosinc.com>
Subject: Re: [PATCH] riscv: deprecate CONFIG_MMU=n
Date: Tue, 27 Feb 2024 10:11:41 +0100	[thread overview]
Message-ID: <a49546e8-6749-4458-98da-67fd37b7df18@rivosinc.com> (raw)
In-Reply-To: <CAGu26P_v9FjYq9Bncvfd-dBhdHQevvN3HpO1nqjA2hYFCpG7hg@mail.gmail.com>

On 26/02/2024 20:00, Charles Lohr wrote:
> WOAH! Please DO NOT deprecate NOMMU. I use the NOMMU build constantly
> and NOMMU Linux on RISC-V is the avenue used by many FPGA soft cores
> for Linux, as well as some limited systems.
> 
> I get new copies of the kernel when there are releases and test them
> frequently to make sure everything is still working as expected.
> 
> For us we just don't care about XIP. I mean if someone did push it
> through to fruition, I'd also test and use it, but I urge you please
> do not deprecate this.  While it's sometimes needed a bit of a
> creative build to get everything working, I've never needed to patch
> anything in the kernel beyond patching in a custom console for serial
> output.
> 

Hey Charles,

No worries, we actually did not expected NOMMU to have *so many* users.
I guess deprecating stuff is a good way to have immediate feedback ;).
Having FDPIC psABI to be merged upstream could also probably be a
positive point toward a better NOMMU support.

> I am happy to discuss the possibility of me and or one of the other
> RISC-V soft (FPGA) core people stepping up to try to be more active,
> but so far we've just been very well serviced by the current NOMMU
> Linux setup.

It could probably be nice to have some feedback/Tested-by: from NOMMU
users for new releases then.

Thanks,

Clément

> 
> Charles
> 
> 
> On Mon, Feb 26, 2024 at 8:03 AM Conor Dooley <conor@kernel.org> wrote:
>>
>> On Mon, Feb 26, 2024 at 04:25:24PM +0100, Clément Léger wrote:
>>> I guess I could also mark XIP as deprecated.
>>
>> I'm not so sure, people recently added XIP support to QEMU (and sent
>> kernel fixes in December). XIP is also not nearly as much of a problem
>> to support, there's far less that it does differently, the main barrier
>> was the inability to test it which is no longer the case.
>> That said, XIP is gonna kill itself off I feel as it does not support
>> runtime patching and therefore is extremely limited on extensions, given
>> we use alternatives for all of that (although I suppose if someone has a
>> usecase they could make nasty macros worse and implement a compiletime
>> switch in the alternatives too).
>>
>> Cheers,
>> Conor.
>>
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