Re: [PATCH v2 02/22] asm-generic/io.h: add ioremap_nopost remap interface

[Lorenzo Pieralisi]

On Wed, Apr 05, 2017 at 01:38:12PM +0100, Lorenzo Pieralisi wrote:
> On Wed, Apr 05, 2017 at 11:58:41AM +0100, Russell King - ARM Linux wrote:
> > On Tue, Mar 28, 2017 at 03:45:43PM +0100, Lorenzo Pieralisi wrote:
> > > On Mon, Mar 27, 2017 at 08:41:10PM -0500, Bjorn Helgaas wrote:
> > > > On Mon, Mar 27, 2017 at 10:49:30AM +0100, Lorenzo Pieralisi wrote:
> > > > > diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> > > > > index 7afb0e2..50b292f 100644
> > > > > --- a/arch/x86/include/asm/io.h
> > > > > +++ b/arch/x86/include/asm/io.h
> > > > > @@ -171,6 +171,7 @@ static inline unsigned int isa_virt_to_bus(volatile void *address)
> > > > >  extern void __iomem *ioremap_nocache(resource_size_t offset, unsigned long size);
> > > > >  extern void __iomem *ioremap_uc(resource_size_t offset, unsigned long size);
> > > > >  #define ioremap_uc ioremap_uc
> > > > > +#define ioremap_nopost ioremap_nocache
> > > > 
> > > > These are all the same as the default from asm-generic.h.  Do we really
> > > > need these definitions in alpha, avr32, frv, ia64, x86?
> > > 
> > > Those arches do not include asm-generic.h (I suppose for a good reason)
> > > but a definition is needed anyway if we want code using ioremap_nopost()
> > > to be unconditional. This is one way of doing it, there are others not
> > > sure they are any better, I am open to suggestions.
> > 
> > We do have linux/io.h, which should be included in preference to asm/io.h.
> > linux/io.h has existed for years, but I still see (from time to time)
> > patches adding drivers that (imho incorrectly) use asm/io.h.
> > 
> > Also, this:
> > 
> > > > > diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
> > > > > index 7ef015e..0e81938 100644
> > > > > --- a/include/asm-generic/io.h
> > > > > +++ b/include/asm-generic/io.h
> > > > > @@ -915,6 +915,10 @@ extern void ioport_unmap(void __iomem *p);
> > > > >  #endif /* CONFIG_GENERIC_IOMAP */
> > > > >  #endif /* CONFIG_HAS_IOPORT_MAP */
> > > > >  
> > > > > +#ifndef ioremap_nopost
> > > > > +#define ioremap_nopost ioremap_nocache
> > > > > +#endif
> > > > > +
> > > > >  #ifndef xlate_dev_kmem_ptr
> > > > >  #define xlate_dev_kmem_ptr xlate_dev_kmem_ptr
> > > > >  static inline void *xlate_dev_kmem_ptr(void *addr)
> > 
> > could well be located in linux/io.h, which would make it available
> > everywhere.
> > 
> > I'd suggest one change to this though:
> > 
> > #ifndef ioremap_nopost
> > static inline void __iomem *ioremap_nopost(resource_size_t offset,
> > 					   unsigned long size)
> > {
> > 	return ioremap_nocache(offset, size);
> > }
> > #endif
> > 
> > This way, if someone forgets to define ioremap_nopost() in their
> > asm/io.h but provides a definition or extern prototype for
> > ioremap_nopost(), we end up with a compile error to highlight the
> > error, rather than the error being hidden by the preprocessor.
> 
> Yes, I could add ioremap_nopost() to linux/io.h I did not do it because
> linux/io.h, for whatever reason, does not seem to contain ioremap_*
> prototypes; this does not mean we should not add it there but that
> would look odd (with all others ioremap_* in asm/io.h), all I am
> saying. This stuff requires some clean-up regardless, for the records.
> 
> As for the static inline, I did that and that did not make the
> kbuild robot happy at all on some arches:
> 
> eg: openrisc
> 
> >> include/asm-generic/io.h:922:9: error: implicit declaration of
> >> function 'ioremap_nocache' [-Werror=implicit-function-declaration]
>      return ioremap_nocache(offset, size);

Indeed, the static inline ioremap_nocache() fallback does not work
on all arches (whether I add the fallback in linux/io.h or
asm-generic/io.h is irrelevant), I bump into issues such as the one
reported above.

I could make it:

#ifndef ioremap_nopost
static inline void __iomem *ioremap_nopost(resource_size_t offset,
					   unsigned long size)
{
	return NULL;
}
#endif

which would force arches to define ioremap_nopost() (if they need it).

This is what I *assume* was done for ioremap_uc() in asm-generic/io.h,
but honestly history is hard to follow here.

Thoughts ?

Thanks,
Lorenzo