Re: [PATCH v3 3/3] asm-generic/io.h: Silence -Wnull-pointer-arithmetic warning on PCI_IOBASE

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Wed, 2021-04-21 at 23:19 +0800, kernel test robot wrote:
> Hi Niklas,
> 
> I love your patch! Yet something to improve:
> 
> [auto build test ERROR on soc/for-next]
> [also build test ERROR on asm-generic/master v5.12-rc8 next-20210421]
> [cannot apply to arc/for-next sparc-next/master]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
> 
> url:    https://github.com/0day-ci/linux/commits/Niklas-Schnelle/asm-generic-io-h-Silence-Wnull-pointer-arithmetic-warning-on-PCI_IOBASE/20210421-192025
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git for-next
> config: riscv-nommu_k210_defconfig (attached as .config)
> compiler: riscv64-linux-gcc (GCC) 9.3.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/0day-ci/linux/commit/05bc9b9b640336015712d139ebc42830d12a82da
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review Niklas-Schnelle/asm-generic-io-h-Silence-Wnull-pointer-arithmetic-warning-on-PCI_IOBASE/20210421-192025
>         git checkout 05bc9b9b640336015712d139ebc42830d12a82da
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross W=1 ARCH=riscv 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from arch/riscv/include/asm/clint.h:10,
>                     from arch/riscv/include/asm/timex.h:15,
>                     from include/linux/timex.h:65,
>                     from include/linux/time32.h:13,
>                     from include/linux/time.h:60,
>                     from include/linux/stat.h:19,
>                     from include/linux/module.h:13,
>                     from init/main.c:17:
>    include/asm-generic/io.h: In function 'inb_p':
> > > arch/riscv/include/asm/io.h:55:65: error: 'PCI_IOBASE' undeclared (first use in this function)
>       55 | #define inb(c)  ({ u8  __v; __io_pbr(); __v = readb_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })

Interesting, it looks to me like RISC-V sets PCI_IOBASE to 
((void __iomem *)PCI_IO_START) if running with an MMU but leaves it
undefined without an MMU. It does then use its own (broken?) inb/w/l()
macros with PCI_IOBASE 0 from asm-generic/io.h. What a mess ;-(