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From: David Mosberger <davidm@napali.hpl.hp.com>
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Date: Tue, 24 Sep 2002 10:11:26 -0700
To: Dave Olien <dmo@osdl.org>
Cc: "David S. Miller" <davem@redhat.com>, phillips@arcor.de, davidm@hpl.hp.com,
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Subject: Re: DAC960 in 2.5.38, with new changes
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>>>>> On Tue, 24 Sep 2002 09:54:56 -0700, Dave Olien <dmo@osdl.org> said:

  Dave> According to the Documentation/DMA-mapping.txt file, the new
  Dave> DMA mapping interfaces should allow all PCI transfers to use
  Dave> 32-bit DMA addresses. Controllers on the PCI bus should never
  Dave> need to use DAC PCI transfers.  Based on this, writel() should
  Dave> work even on ia64.

Warning: there is a big difference between *can* and *want*.  On ia64
machines with an Intel chipset, the PCI DMA interface is implemented
via bounce buffers, so it will be *much* slower than DAC.  For this
reason, it is preferable on ia64 to use DAC where possible (and just
in case Dave Miller starts asking about this: yes, the hp zx1 chipset
for Itanium 2 does have a hardware I/O TLB... ;-).

	--david
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