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From: David Mosberger <davidm@napali.hpl.hp.com>
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Date: Tue, 24 Sep 2002 11:21:45 -0700
To: Dave Olien <dmo@osdl.org>
Cc: davidm@hpl.hp.com, "David S. Miller" <davem@redhat.com>, phillips@arcor.de,
       davidm@napali.hpl.hp.com, axboe@suse.de, _deepfire@mail.ru,
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Subject: Re: DAC960 in 2.5.38, with new changes
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>>>>> On Tue, 24 Sep 2002 10:28:43 -0700, Dave Olien <dmo@osdl.org> said:

  Dave> Hmm, interesting.  A big part of what I'm doing to the driver
  Dave> right now is plugging in calls to the PCI DMA interfaces.

That's fine (actually, it's more than that: it's great!).

  Dave> So unless the underlying implementation is aware of these
  Dave> platform limitations and "doing the right thing", I'm adding
  Dave> a bunch of bounce buffer activity for many ia64 platforms.
  Dave> That would be too bad.

The idea is to do something along these lines:

 o Use PCA DMA interface for managing all DMA buffers.

 o If sizeof(dma_addr_t) > 4, turn on DAC mode and call
   pci_set_dma_mask(dev, MAX_ADDR), where MAX_ADDR is the maximum
   address that can be reached by the controller (i.e.,
   0xffffffffffffffff for a truly 64-bit-capable PCI controller).

This way, everything should work out correctly and with good
performance on all imaginable platforms (ia64 with and without
hardware I/O TLB, plain x86, x86 with >4GB RAM, SPARC64 with 32-bit
dma_addr_t, etc.).

	--david
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