Re: (reposting) how to get DMA'able memory within 4GB on 64-bit machine

From: Martin Wilck (
Date: Mon Jul 16 2001 - 11:51:10 EST


sorry to join in so late in this thread, but I think I should bring the
following to your attention:

Someone (David, I think) said that IA64 was handling 32-bit controllers
fine. To my experience, that depends strongly on the drivers.
At least for aic7xxx, it is not the case (I have documented the
related crashes on the linux-ia64 mailing lists during the last two
months). The driver is simply eating up buffer space in such vast amounts
that it freezes the software IO-memory management even at very moderate
load (you can use the "old" driver instead, but this doesn't look like a
long-term solution).

After some discussion, Justin Gibbs announced that he'll implement 39-bit
DMA addressing in the aic7xxx driver, and it appeared that this was
pretty much the only viable solution to make the "new" aic7xxx driver work on
IA64. I haven't looked at his new code yet, but I assume he's using the
IA64 approach.

It is likely that this will happen for other drivers as well, especially
those that need a lot of buffer space for good performance. Thus the IA-64
API will probably emerge as a matter-of-fact standard, and if something
better is to replace it, I think it should be decided upon quickly, so
that driver maintainers (and IA64) can adopt to it before everything has
to be written (and debugged) twice.


Martin Wilck     <>
FSC EP PS DS1, Paderborn      Tel. +49 5251 8 15113

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