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

[Luis R. Rodriguez]

On Thu, Apr 06, 2017 at 11:26:36AM +0100, Lorenzo Pieralisi wrote:
> 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.

Its also not *safe* to assume on behalf of all architectures a new ioremap
call is both a good idea and proper.

> 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).

Yes, please do this.

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

Hard to follow ?

I think commit 8c7ea50c010b2 ("x86/mm, asm-generic: Add IOMMU ioremap_uc()
variant default") makes it very clear that historically we have made bad
assumptions and these assumptions are not safe, so the only correct thing we
can do to not stall development is to do what you did above, and each
architecture then can add support for its proper mapping. Its up to each
architecture maintainer to be attentive and review these patches, if they don't
get to it, this will just not work for the new driver that needs it, such is
life, its better than having incorrect defaults spread for all architectures.

The old strategy was very sloppy. Its why I tried to be as clear as possible on
both the commit log and headers about this. If the commit log and headers were
not clear, please help clarify this more somehow in your patches.

  Luis