Re: [PATCH] ARM: ep93xx: remove MaverickCrunch support

From: Arnd Bergmann <arnd@kernel.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Martin Guy <martinwguy@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	 Hartley Sweeten <hsweeten@visionengravers.com>,
	 Alexander Sverdlin <alexander.sverdlin@gmail.com>,
	SoC Team <soc@kernel.org>,
	 Nikita Shubin <nikita.shubin@maquefel.me>,
	Arnd Bergmann <arnd@arndb.de>,  Oleg Nesterov <oleg@redhat.com>,
	Hubert Feurstein <hubert.feurstein@contec.at>,
	 Lukasz Majewski <lukma@denx.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	 Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 linux-kernel <linux-kernel@vger.kernel.org>,
	 clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] ARM: ep93xx: remove MaverickCrunch support
Date: Tue, 3 Aug 2021 14:29:00 +0200	[thread overview]
Message-ID: <CAK8P3a0QTxd4ghTYz7kRWnxLrL8hBQ1PwNuR4ptLw-dOkKmPPg@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdbRbgjo1AkZVd0J1nhuo601o8=20rKR+ccaJR1+vqn6qg@mail.gmail.com>

On Tue, Aug 3, 2021 at 2:12 PM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Mon, Aug 2, 2021 at 5:45 PM Martin Guy <martinwguy@gmail.com> wrote:
>
> > > was removed from gcc in its 4.8 release in 2012.
> >
> > I was sad about that, as I had managed to get it working correctly in
> > 4.2 4.3 and 4.4.
> > Unfortunately the GCC ARM maintainer at the time was paid by ARM, and
> > they had no interest in it, as I gather the ARM-Cirrus partnership
> > ended up disappointingly.
>
> Political issues aside, have you considered contributing support
> to LLVM instead?
>
> It currently doesn't even support ARMv4 AFAIK but reportedly
> has an easier to use and maintain back-end. (I do not know if
> this is true, I just browsed this:
> https://llvm.org/docs/WritingAnLLVMBackend.html )
> Current ARM Targets are here:
> https://github.com/llvm/llvm-project/tree/main/llvm/lib/Target/ARM
> And they have a very clear and straight-forward developer policy:
> https://llvm.org/docs/DeveloperPolicy.html
>
> If ARMv4 support could be added to LLVM, that would solve
> a lot of my headaches for ARM32, where we have things like
> SA110 being actively maintained.

I think for ARMv4 support, the only thing we need from llvm is
to have R_ARM_V4BX relocations, and for lld to support the
--fix-v4bx switch that turns 'bx' instructions into 'mov' when those
relocations are found. This is something that we have previously
discussed with the llvm developers and that may easily happen.

For the Crunch support, I don't think it's worth spending any effort
on adding that to llvm. If there are any remaining users, they have
probably stopped upgrading their user space long ago (to be
confirmed). The SoC itself has been "not recommended for new
design" since 2019, so we are unlikely to see new users of the platform
in the future, and I think existing users are equally unlikely to move
from softfp to crunch even if they have the option.

       Arnd