Messages in this thread | | | Date | Tue, 28 Feb 2006 17:08:05 +0100 | From | Jes Sorensen <> | Subject | Re: [PATCH] Define wc_wmb, a write barrier for PCI write combining |
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Roland Dreier wrote: > Jes> Could you explain why the current mmiowb() API won't suffice > Jes> for this? It seems that this is basically trying to achieve > Jes> the same thing. > > I don't believe mmiowb() is at all the same thing. mmiowb() is all > about ordering writes between _different_ CPUs without incurring the > cost of flushing posted writes by issuing a read on the bus.
Not quite correct as far as I understand it. mmiowb() is supposed to guarantee that writes to MMIO space have completed before continuing. That of course covers the multi-CPU case, but it should also cover the write-combining case.
> wc_wmb() > would just act like a true wmb(), even when using write-combining > regions on x86 -- in other words, there would be no cross-CPU synchronization.
I wary of adding yet another variation unless there is a clear distinction between them that is easy to understandn for driver authors.
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