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From: Charles Lohr <lohr85@gmail.com>
Date: Tue, 26 Mar 2024 18:34:09 -0700
Message-ID: <CAGu26P-CqdsQzNTNDidBUg=pxU3vs7QhNEajokGKe7p8M2sLBA@mail.gmail.com>
Subject: Re: [PATCH] riscv: deprecate CONFIG_MMU=n
To: Jisheng Zhang <jszhang@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>, cleger@rivosinc.com, 
	Conor Dooley <conor@kernel.org>, samuel.holland@sifive.com, 
	Paul Walmsley <paul.walmsley@sifive.com>, aou@eecs.berkeley.edu, 
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, 
	Conor Dooley <conor.dooley@microchip.com>, ajones@ventanamicro.com, dlemoal@kernel.org, 
	Bjorn Topel <bjorn@rivosinc.com>, Atish Patra <atishp@rivosinc.com>
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Sorry, if you don't mind clarifying, do you know which version you
used, where you got it, and if you had to apply any patches?

Charles

On Tue, Mar 26, 2024 at 6:28=E2=80=AFPM Jisheng Zhang <jszhang@kernel.org> =
wrote:
>
> On Tue, Mar 26, 2024 at 01:25:08PM -0700, Charles Lohr wrote:
> > Jisheng, are you using musl or uclibc? I've been having difficulty
> > getting new versions of each working with the newer kernels with
> > system calls not lining up.
>
> Hi Charles,
>
> I tested nommu linux with uclibc, both rv32 and rv64
>
> Thanks
>
> >
> > Also, is there a better place to ask questions about the more
> > user-spacy stuff?  That's really where I've been struggling to
> > maintain things, keeping buildroot working when targeting RV32 NOMMU.
> > Thankfully a lot of the stickiest problems have all been upstreamed.
> >
> > Charles
> >
> > On Mon, Mar 25, 2024 at 10:12=E2=80=AFAM Jisheng Zhang <jszhang@kernel.=
org> wrote:
> > >
> > > On Thu, Mar 14, 2024 at 09:02:43PM +0800, Jisheng Zhang wrote:
> > > > On Thu, Mar 14, 2024 at 08:46:21PM +0800, Jisheng Zhang wrote:
> > > > > On Tue, Feb 27, 2024 at 08:38:50AM -0800, Palmer Dabbelt wrote:
> > > > > > On Tue, 27 Feb 2024 01:11:41 PST (-0800), cleger@rivosinc.com w=
rote:
> > > > > > >
> > > > > > >
> > > > > > > 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 s=
oft cores
> > > > > > > > for Linux, as well as some limited systems.
> > > > > >
> > > > > > OK.
> > > > > >
> > > > > > I just build test this stuff, as I don't really have a use for =
it
> > > > > > personally.  I figured if nobody's reporting bugs then probably=
 it's broken
> > > > > > and nobody's noticed because nobody's using it.
> > > > > >
> > > > > > > > I get new copies of the kernel when there are releases and =
test them
> > > > > > > > frequently to make sure everything is still working as expe=
cted.
> > > > > >
> > > > > > I'd actually expected it to be broken, but I guess we managed t=
o avoid
> > > > > > screwing things up ;)
> > > > > >
> > > > > > > > For us we just don't care about XIP. I mean if someone did =
push it
> > > > >
> > > > > I don't care XIP either, and IMHO the XIP's maintenance effort is=
 much
> > > > > bigger than NOMMU(just check the various XIP_FIXUP* or CONFIG_XIP=
_KERNEL
> > > > > macros around lowlevel pgtable.h, page.h). If we can remove XIP, =
the
> > > > > code readability will be much better.
> > > > >
> > > > > Or sending out a similar XIP deprecation patch to see whether the=
re's
> > > > > any complain ? ;)
> > > > >
> > > > > > > > through to fruition, I'd also test and use it, but I urge y=
ou please
> > > > > > > > do not deprecate this.  While it's sometimes needed a bit o=
f a
> > > > >
> > > > > +1 for urge the upstream please do not deprecate NOMMU.
> > > > >
> > > > > Besides the soft(FPGA) core mentioned by Charles, here is another=
 real
> > > >
> > > > And I'd like to write more about soft core: riscv is a free and ope=
n
> > > > ISA, this make it really good for education, for simple riscv
> > > > implementation or emulator. Once riscv IMA is implemented(even if M=
MU,
> > > > cache, TLB stuff don't exist), it's not far away from making linux
> > > > running on the FPGA or emulator. If the gain is larger than the mai=
ntenance
> > > > effort, I'd like to urge keeping the NOMMU support.
> > > >
> > > > Thanks a lot
> > > >
> > > > > usage case: As is known, Sophgo CV1800B platforms such as Milk Du=
o
> > > > > contains two C906 core, one(a.k.a big core) with MMU another(a.k.=
a small
> > > > > core)w/o MMU. The vendor sdk runs freertos on the small core, but=
 it
> > > > > doesn't prevent users to run other OS such as threadx, zephyr or =
nommu
> > > > > linux on the small core. In fact, I sucessfully brought up nommu =
linux
> > > > > on the small core. I didn't just send out the patches in time dur=
ing this
> > > > > dev window duo to my personal career reason(I spent the time on h=
unting
> > > > > for a new job)
> > > > >
> > > > > I plan to send out NOMMU related patches once 6.9-rc1 is out.
> > >
> > > As is promised, the NOMMU improvement patches are sent out
> > > https://lore.kernel.org/linux-riscv/20240325164021.3229-1-jszhang@ker=
nel.org/T/#t
> > >
> > > Thanks
> > >
> > > > >
> > > > > > > > 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 ma=
ny* users.
> > > > > > > I guess deprecating stuff is a good way to have immediate fee=
dback ;).
> > > > > > > Having FDPIC psABI to be merged upstream could also probably =
be a
> > > > > > > positive point toward a better NOMMU support.
> > > > > >
> > > > > > Ya, that's probably the right way to do it.  Touching anything =
in the psABI
> > > > > > is pretty miserable, though, so I don't really want to force pe=
ople to do
> > > > > > it...
> > > > > >
> > > > > > > > I am happy to discuss the possibility of me and or one of t=
he other
> > > > > > > > RISC-V soft (FPGA) core people stepping up to try to be mor=
e active,
> > > > > > > > but so far we've just been very well serviced by the curren=
t NOMMU
> > > > > > > > Linux setup.
> > > > > > >
> > > > > > > It could probably be nice to have some feedback/Tested-by: fr=
om NOMMU
> > > > > > > users for new releases then.
> > > > > >
> > > > > > Having more upstream interaction from users is always appreciat=
ed, that's
> > > > > > the best way to prove people are using the code.  If you guys h=
ave the time
> > > > > > it'd be great to get this into some sort of CI, ideally running=
 on some real
> > > > > > platform.
> > > > >
> > > > > As above, I'd also like to step up on the NOMMU stuff, at least t=
est
> > > > > nommu on milkv duo's small core. And can be seen from my git comm=
it
> > > > > histotry, I was active, and I belive I will still be active on ri=
scv linux
> > > > > kernel development.
> > > > >
> > > > > >
> > > > > > > Thanks,
> > > > > > >
> > > > > > > Cl=C3=A9ment
> > > > > > >
> > > > > > > >
> > > > > > > > Charles
> > > > > > > >
> > > > > > > >
> > > > > > > > On Mon, Feb 26, 2024 at 8:03=E2=80=AFAM Conor Dooley <conor=
@kernel.org> wrote:
> > > > > > > > >
> > > > > > > > > On Mon, Feb 26, 2024 at 04:25:24PM +0100, Cl=C3=A9ment L=
=C3=A9ger wrote:
> > > > > > > > > > I guess I could also mark XIP as deprecated.
> > > > > > > > >
> > > > > > > > > I'm not so sure, people recently added XIP support to QEM=
U (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, th=
e 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 ex=
tensions, given
> > > > > > > > > we use alternatives for all of that (although I suppose i=
f someone has a
> > > > > > > > > usecase they could make nasty macros worse and implement =
a compiletime
> > > > > > > > > switch in the alternatives too).
> > > > > > > > >
> > > > > > > > > Cheers,
> > > > > > > > > Conor.
> > > > > > > > >
> > > > > > > > > _______________________________________________
> > > > > > > > > linux-riscv mailing list
> > > > > > > > > linux-riscv@lists.infradead.org
> > > > > > > > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> > > > > >
> > > > > > _______________________________________________
> > > > > > linux-riscv mailing list
> > > > > > linux-riscv@lists.infradead.org
> > > > > > http://lists.infradead.org/mailman/listinfo/linux-riscv