linux-kernel - Re: [PATCH] ARM: makefile: use ARMv3M mode for RiscPC

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Message-ID: <CAK8P3a06uOvGcju7MppqqhsR5dwPKUBawrDbGYNXURqxGsZOKw@mail.gmail.com>
Date:   Tue, 2 Oct 2018 15:53:55 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        arm-soc <arm@...nel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>
Subject: Re: [PATCH] ARM: makefile: use ARMv3M mode for RiscPC

On Tue, Oct 2, 2018 at 3:28 PM Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
>
> On 2 October 2018 at 15:20, Jason A. Donenfeld <Jason@...c4.com> wrote:
> > The purpose of CONFIG_CPU_32v3 is to avoid ldrh/strh on the RiscPC,
> > which is pretty much an ARMv4 device, except its bus will choke on the
> > half-words. The way to make the C compiler not output ldrh/strh is with
> > -march=armv3, which doesn't support them in the ISA. However, this
> > prevents certain cryptography code from working that uses instructions
> > like umull. Fortunately there's also -march=armv3m that does support
> > those, making it possible to continue assembling optimized cryptography
> > routines for our beloved RiscPC.
> >
> > Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> > Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > Cc: Russell King <linux@...linux.org.uk>
> > Cc: Arnd Bergmann <arnd@...db.de>
>
> Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

Acked-by: Arnd Bergmann <arnd@...db.de>

Please add this to Russell's patch tracker for inclusion at
http://www.arm.linux.org.uk/developer/patches/

      Arnd