Re: [PATCH v5 2/6] arch: unify ioremap prototypes and macro aliases

[Christoph Hellwig <hch@lst.de>]

On Tue, Jun 30, 2015 at 03:57:16PM -0700, Dan Williams wrote:
> > void __iomem *ioremap_flags(resource_size_t offset, unsigned long size,
> >                         unsigned long prot_val, unsigned flags);
> 
> Doesn't 'flags' imply a specific 'prot_val'?

Looks like the values are arch specific.  So as a first step I'd like
to keep them separate.  As a second step we could look into unifying
the actual ioremap implementations which look mostly the same.  Once
that is done we could look into collapsing the flags and prot_val
arguments.

> One useful feature of the ifdef mess as implemented in the patch is
> that you could test for whether ioremap_cache() is actually
> implemented or falls back to default ioremap().  I think for
> completeness archs should publish an ioremap type capabilities mask
> for drivers that care... (I can imagine pmem caring), or default to
> being permissive if something like IOREMAP_STRICT is not set.  There's
> also the wrinkle of archs that can only support certain types of
> mappings at a given alignment.

I think doing this at runtime might be a better idea.  E.g. a
ioremap_flags with the CACHED argument will return -EOPNOTSUP unless
actually implemented.  On various architectures different CPUs or
boards will have different capabilities in this area.

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