[Ksummit-discuss] [TECH TOPIC] Semantics of MMIO mapping attributes accross archs

[Benjamin Herrenschmidt]

On Sat, 2015-07-04 at 07:12 -0700, Dan Williams wrote:

> Another side topic that has come up in this space is the desire to
> define a "memremap" api to clean up __iomem abuses for cases where
> "memory-like" mappings are needed.
> 
> https://lkml.org/lkml/2015/6/22/100

Interesting. I had missed this. There is a similar question about
semantics (ordering etc...), ie, are they the same as memory for
example ?

Another thing we might look into is to what extent should we provide
access to the "SAO" mapping attribute that POWER7 and later support
(strong ordering, pretty-much x86 like) and whether this can be used
on ppc to reduce the need for barriers (that attribute is only available
for fully cachable mappings, not generally applicable to IO mappings).

That translate to: should your new memremap() take some kinds of flags
as an argument ? Though of course providing a cross-arch definition of
these flags would be tricky.
 
Ben.