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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 10 Mar 2022 08:39:51 +0100
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Subject: Re: [lpieralisi-pci:pci/rcar 2/2] drivers/pci/controller/pcie-rcar-host.c:139:3:
 error: instruction requires: data-barriers
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Bjorn Helgaas <helgaas@kernel.org>,
        kernel test robot <lkp@intel.com>,
        Marek Vasut <marek.vasut+renesas@gmail.com>,
        llvm@lists.linux.dev, kbuild-all@lists.01.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Ard Biesheuvel <ardb@kernel.org>
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On Thu, Mar 10, 2022 at 1:18 AM Nathan Chancellor <nathan@kernel.org> wrote:

> > To avoid this error, for now I have cherry-picked de6b5097f58b to a
> > local pci/host/rcar branch and dropped 9775965dbae5.
>
> FWIW, this is not clang specific, the same configuration blows up with
> GCC 11.2.0 as well:
>
> $ make -skj"$(nproc)" \
>        ARCH=arm \
>        CROSS_COMPILE=arm-linux-gnueabi- \
>        olddefconfig drivers/pci/controller/pcie-rcar-host.o
> /tmp/ccz8ybtm.s: Assembler messages:
> /tmp/ccz8ybtm.s:742: Error: selected processor does not support `isb' in ARM mode
> /tmp/ccz8ybtm.s:812: Error: selected processor does not support `isb' in ARM mode
> make[4]: *** [scripts/Makefile.build:288: drivers/pci/controller/pcie-rcar-host.o] Error 1
>
> $ rg CONFIG_CPU_32 .config
> 289:CONFIG_CPU_32v4=y
>
> It does not look like isb can be used with this configuration, at least
> if I understand arch/arm/include/asm/barrier.h correctly.

My first thought was to amend the #ifdef to

#if IS_ENABLED(CONFIG_ARM) && IS_ENABLED(CONFIG_ARCH_RENESAS)

However, this is still broken because you can build a kernel that
enables the Renesas ARMv7 platform along with early ARMv6 (omap2 and
imx3) that do not support "isb" either.

What I think we want to do here instead is to add a ".arch armv7-a" in the
inline assembly.

        Arnd