Re: [RFC] MMIO accessors & barriers documentation

[Eric W. Biederman]

Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> writes:

> I've not gone too much in details about write combining (we need to do
> something about it but I don't want to mix problems) but I did define
> that the ordered accessors aren't guaranteed to provide write combining
> on storage mapped with WC enabled while the relaxed or non ordered ones
> are. That should be enough at this point.

Sounds good.

> Later, we should look into providing an ioremap_wc() and possibly page
> table flags for write combining userland mappings. Time to get rid of
> MTRRs for graphics :) And infiniband-style stuff seems to want that too.

ioremap_wc is actually the easy half.  I have an old patch that handles
that.  The trick is to make certain multiple people don't map the same
thing with different attributes.  Unfortunately I haven't had time to
work through that one yet.

Eric

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