Re: [Linux-ia64] 2.4.16-ia64-011128 is missing dma64_addr_t

["Gérard Roudier" <groudier@free.fr>]

On Tue, 4 Dec 2001, David Mosberger wrote:

> >>>>> On Tue, 4 Dec 2001 09:45:19 +0100, Christoph Hellwig <hch@caldera.de> said:
>
>   Christoph> On Mon, Dec 03, 2001 at 11:34:28AM -0800, David Mosberger
>   Christoph> wrote:
>   >> This error appears to be due to a bug in the sym53c8xx_2 driver.
>   >> Note that dma64_addr_t should be used only for the pci_dac_*
>   >> interface, which I do not want to support on ia64 unless and
>   >> until we absolutely have to (technically, there is no need for
>   >> pci_dac_* on ia64 or x86).
>
>   Christoph> IA64 should use instead of it's horrible iommu emulation.
>
> Huh?  pci_dac_*() does not help you here at all.  pci_dac_*() is only
> needed/useful for 64-bit platforms which use a dma_addr_t that is
> smaller than 64 bits.  And even then is it needed only for drivers
> that create tons of mappings.

I am under the impression that it has been invented for sparc64 as a
provision for PCI devices that may gain advantage of real 64 bit DMA PCI
on this hardware. This platform has some streaming mode DMA implemented
for 32 bit PCI through an IO/MMU.

Choices are:

1) Faster IOs but only in 32 bit PCI mode + software complexity as a
   malus.
2) Slower IOs in 64 bit PCI mode.

Chosing the less bad one, here choice #1, is what is to be done when no
good choice is available.

  Gérard.