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From: David Mosberger <davidm@napali.hpl.hp.com>
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Date: Tue, 24 Sep 2002 12:12:29 -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 11:25:19 -0700, Dave Olien <dmo@osdl.org> said:

  Dave> Ok, thanks for explaining!

  Dave> On Tue, Sep 24, 2002 at 11:21:45AM -0700, David Mosberger wrote:
  >> >>>>> On Tue, 24 Sep 2002 10:28:43 -0700, Dave Olien <dmo@osdl.org> said:
  >>
  >> 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.).

Come to think of it, the following refinement may be preferable:

 o Use PCA DMA interface for managing all DMA buffers.

 o limit = min(~(dma_addr_t) 0, 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).

 o Call pci_set_dma_mask(dev, limit).

 o If limit > 0xffffffff, turn on DAC mode.

This "algorithm" should be correct for all PCI controllers.

	--david
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