[Linux-ia64] Re: 64 Bits DMA Addresses for Alloc Consistent Interfaces.

From: Colin Ngam <cngam_at_sgi.com>
Date: 2003-05-16 09:25:54
James Bottomley wrote:

> On Thu, 2003-05-15 at 17:44, Colin Ngam wrote:
> > However, in PCI-X mode, we do not have the capability to generate SAC addresses.
> > And yes, you are also correct that it is very much efficient on our architecture
> > to generate DAC for all(PCI/PCI-X)
> >
> > So, it is a hard requirement to have DAC for PCI-X devices and not PCI devices.
> >
> > Hope that is clear ..
> Actually, no.  This seems to imply that your PCI-X cards can *never*
> access the first 4GB of memory (because they can't use an IOMMU and they
> have to generate a DAC cycle with non zero in bits 63--32).

Actually, our system does not have Physical Memory Address smaller than
48Bits - give or take couple bits ...  Hence, 32Bits Mapped DMA address
maps to 48Bits System Physical Address.

64Bits Mapped DMA address maps directly to System Physical Memory
with Bits 63-49 containing transfer attributes like hardware support
for byte swapping .. if needed(e.g. Big Endian Cards).



> James
Received on Thu May 15 16:43:33 2003

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