Re: DMA from/to user-space memory

David S. Miller (
Fri, 15 May 1998 14:17:29 -0700

From: Benny Amorsen <>
Date: 15 May 1998 23:16:43 +0200

>>>>> "DSM" == David S Miller <> writes:

DSM> I also agree with Robert that making part of the DMA interface
DSM> cater to ISA 16MB limitations is likely to be totally unused by
DSM> anyone. (I'm happy to be shown wrong, if you can think of a
DSM> useful and legitimate counterexample, speak up ;-)

How about catering to PCI 4GB limitations on 64 bit architectures?

On the 64-bit architectures I know of, and PCI as specified, is not
limited to 64-bits of physical addressing.

But back to reality, yes most cards don't implement dual address
cycles at all. We could have the interface use GFP_DMA, which on
sparc64 for example gets you a page in the lower 32-bits of physical
address space.

David S. Miller

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