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

Christoph Hellwig
2015-07-01T06:24:07Z

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.