PCI MMIO flushing, write-combining etc

From: Krzysztof Halasa (khc@pm.waw.pl)
Date: Thu Aug 15 2002 - 18:45:54 EST


Just a few simple questions for you PCI experts (please correct any wrong

Imagine we have a PCI card with 2 MMIO regions: prefetchable PR1 and
non-prefetchable NPR2 (and we are not limited to Pentium-class machines).

I understand writes to PR1 can be reordered, merged, and delayed.
What should I do to flush the write buffers? I understand reading from
PR1 would do. Would reading from NPR2 flush PR1 write buffers?
Would writing to NPR2 flush them?

Now NPR2, the non-prefetchable MMIO region.
Is it possible that the writes there are reordered, merged and/or
delayed (delayed = not making it to the PCI device when the writel()

We have ioremap() and ioremap_nocache(). What is the exact difference
between them? Would the ioremap_nocache() disable all A) read- and
B) write-caching on a) prefetchable MMIO b) non-prefetchable MMIO ?

Would the ioremap() enable A) read- and A) write-caching on
a) prefetchable MMIO b) non-prefetchable MMIO ?

Thank you.

Krzysztof Halasa
Network Administrator
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