Messages in this thread | | | Date | Tue, 30 Apr 2002 20:56:42 +0100 | From | arjan@fenrus ... | Subject | Re: How to write portable MMIO code? |
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In article <Pine.LNX.4.44.0204301112520.32217-100000@chaos.physics.uiowa.edu> you wrote: >> - should one in general (i.e., assuming the worst case) do wmb() on >> writes, and mb() on reads?
readl() and writel() are specified to contain the proper barriers already.
> I don't think mb() will help you. You're probably experiencing PCI posting > problems - when a writel() has executed, that doesn't necessarily mean > that the transaction has actually happened it may (and will) be buffered > for a potentially long time. > > However, PCI won't reorder reads vs. writes, so you when you want to be > sure that a write() actually reached the hardware, do a dummy read() > afterwards, that'll flush the write buffer.
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