On Mon, Jul 27, 2015 at 4:43 PM, Luis R. Rodriguez <mcgrof(a)suse.com> wrote:
On Mon, Jul 27, 2015 at 04:31:09PM -0700, Dan Williams wrote:
> On Mon, Jul 27, 2015 at 4:17 PM, Luis R. Rodriguez <mcgrof(a)suse.com> wrote:
> > On Fri, Jul 24, 2015 at 10:38:42PM -0400, Dan Williams wrote:
> >> Existing users of ioremap_cache() are mapping memory that is known in
> >> advance to not have i/o side effects. These users are forced to cast
> >> away the __iomem annotation, or otherwise neglect to fix the sparse
> >> errors thrown when dereferencing pointers to this memory. Provide
> >> memremap() as a non __iomem annotated ioremap_*() in the case when
> >> ioremap is otherwise a pointer to memory.
> > Ok so a special use case.
> >> Outside of ioremap() and
> >> ioremap_nocache(), the expectation is that most calls to
> >> ioremap_<type>() are seeking memory-like semantics (e.g. speculative
> >> reads, and prefetching permitted). These callsites can be moved to
> >> memremap() over time.
> > Such memory-like smantics are not well defined yet and this has caused
> > issues over expectations over a slew of APIs. As you note above
> > your own defined 'semantics' so far for memremap are just that there
> > no i/o side effects, when the mapped memory is just a pointer to memory,
> > as such I do not think its fair to set the excpectations that we'll
> > switch all other ioremap_*() callers to the same memremap() API. Now,
> > it may be a good idea to use something similar, ie, to pass flags,
> > but setting the expectations outright to move to memremap() without having
> > any agreement having been made over semantics seems uncalled for at this
> > point in time, specially when you are noting that the expectations for
> > both sets of calls are different.
> > So perhaps:
> > "
> > Outside of ioremap() and ioremap_nocache(), all other ioremap_<type>()
> > variant calls are seeking memory-like semantics (e.g. speculative
> > reads, and prefetching permitted) and all calls expecations currently
> > differ depending on architecture. Once and if we get agreement on such
> > semantics we may be able to move such ioremap_*() variant calls to
> > a similar API where the semantics required are clearly spelled out
> > and well defined and passed as arguments.
> I still think ioremap_wc(), and now ioremap_uc(), are special and are
> not obvious candidates for conversion to memremap().
OK great, then we're in strong agreement, so removing the "Outside of
ioremap() and... over time" might be best then? Otherwise what I posted
seems to reflect the state of affairs better?
Ah yes, I need to clean that up. Thanks!