[RFT PATCH v3 08/27] asm-generic/io.h: Add a non-posted variant of ioremap()

[Will Deacon]

On Thu, Mar 25, 2021 at 11:07:40PM +0900, Hector Martin wrote:
> On 25/03/2021 04.09, Arnd Bergmann wrote:
> > On Wed, Mar 24, 2021 at 7:12 PM Will Deacon <will at kernel.org> wrote:
> > > 
> > > > +/*
> > > > + * ioremap_np needs an explicit architecture implementation, as it
> > > > + * requests stronger semantics than regular ioremap(). Portable drivers
> > > > + * should instead use one of the higher-level abstractions, like
> > > > + * devm_ioremap_resource(), to choose the correct variant for any given
> > > > + * device and bus. Portable drivers with a good reason to want non-posted
> > > > + * write semantics should always provide an ioremap() fallback in case
> > > > + * ioremap_np() is not available.
> > > > + */
> > > > +#ifndef ioremap_np
> > > > +#define ioremap_np ioremap_np
> > > > +static inline void __iomem *ioremap_np(phys_addr_t offset, size_t size)
> > > > +{
> > > > +     return NULL;
> > > > +}
> > > > +#endif
> > > 
> > > Can we implement the generic pci_remap_cfgspace() in terms of ioremap_np()
> > > if it is supported by the architecture? That way, we could avoid defining
> > > both on arm64.
> > 
> > Good idea. It needs a fallback in case the ioremap_np() fails on most
> > architectures, but that sounds easy enough.
> > 
> > Since pci_remap_cfgspace() only has custom implementations, it sounds like
> > we can actually make the generic implementation unconditional in the end,
> > but that requires adding ioremap_np() on 32-bit as well, and I would keep
> > that separate from this series.
> 
> Sounds good; I'm adding a patch to adjust the generic implementation and
> remove the arm64 one in v4, and we can then complete the cleanup for other
> arches later.

Cheers. Don't forget to update the comment in the generic code which
complains about the lack of an ioremap() API for non-posted writes ;)

Will