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

[David Laight <David.Laight@ACULAB.COM>]

From: Arnd Bergmann
> Sent: 13 April 2021 13:27
> 
> On Tue, Apr 13, 2021 at 1:54 PM Niklas Schnelle <schnelle@linux.ibm.com> wrote:
> >
> > When PCI_IOBASE is not defined, it is set to 0 such that it is ignored
> > in calls to the readX/writeX primitives. While mathematically obvious
> > this triggers clang's -Wnull-pointer-arithmetic warning.
> 
> Indeed, this is an annoying warning.
> 
> > An additional complication is that PCI_IOBASE is explicitly typed as
> > "void __iomem *" which causes the type conversion that converts the
> > "unsigned long" port/addr parameters to the appropriate pointer type.
> > As non pointer types are used by drivers at the callsite since these are
> > dealing with I/O port numbers, changing the parameter type would cause
> > further warnings in drivers. Instead use "uintptr_t" for PCI_IOBASE
> > 0 and explicitly cast to "void __iomem *" when calling readX/writeX.

Since the definitions make no sense when PCI_IOBASE in undefined
maybe the functions should either not be defined, be stubs that
do nothing or stubs that are BUG().

	David

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