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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Tue, 10 Aug 2021 13:33:52 +0200
Message-ID: <CAK8P3a3KTaa-AwCOjhaASMx63B3DUBZCZe6RKWk-=Qu7xr_ijQ@mail.gmail.com>
Subject: Re: [GIT PULL 1/2] asm-generic: rework PCI I/O space access
To:     John Garry <john.garry@huawei.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        linux-pci <linux-pci@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Niklas Schnelle <schnelle@linux.ibm.com>
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On Tue, Aug 10, 2021 at 11:19 AM John Garry <john.garry@huawei.com> wrote:
> On 04/08/2021 09:52, Arnd Bergmann wrote:
>
> This seems a reasonable approach. Do you have a plan for this work? Or
> still waiting for the green light?

I'm rather busy with other work at the moment, so no particular plans
for any time soon.

> I have noticed the kernel test robot reporting the following to me,
> which seems to be the same issue which was addressed in this series
> originally:
>
> config: s390-randconfig-r032-20210802 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project
> 4f71f59bf3d9914188a11d0c41bedbb339d36ff5)
> ...
> All errors (new ones prefixed by >>):
>
>     In file included from drivers/block/null_blk/main.c:12:
>     In file included from drivers/block/null_blk/null_blk.h:8:
>     In file included from include/linux/blkdev.h:25:
>     In file included from include/linux/scatterlist.h:9:
>     In file included from arch/s390/include/asm/io.h:75:
>     include/asm-generic/io.h:464:31: warning: performing pointer
> arithmetic on a null pointer has undefined behavior
> [-Wnull-pointer-arithmetic]
>             val = __raw_readb(PCI_IOBASE + addr);
>
> So I imagine lots of people are seeing these.

Right, this is the original problem that Niklas was trying to solve.

If Niklas has time to get this fixed, I can probably find a way to work
with him on finishing up my proposed patch with the changes you
suggested.

       Arnd