Re: [RFC] MMIO accessors & barriers documentation

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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