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SubjectRe: virt_to_bus and >1G of memory (was MAX_DMA_ADDRESS ...)
   Date: 	Fri, 13 Nov 1998 06:29:52 +0000
From: Jamie Lokier <lkd@tantalophile.demon.co.uk>

One thing I've seen in some drivers is that virt_to_bus doesn't
work on a user-space address, _or_ an address in a module.

Right and I think it should stay this way, you must use normal
physical page references and never vmalloc() or user mapping stuff
when passing around buffers which should be DMA'd from/to

Changing this would cause a lot of headaches for not only Intel, but
various other ports as well. As mentioned in another email, the "walk
the page tables" trick won't even work on sparc64 because no page
tables exist at all for the kernel mappings.

Think about making any changes in this area later in 2.3.x, not now.
And I think our energy right now is best directed at getting 2.2.x out
the door already, not dreaming about proposed cleanups in 2.3.x

Later,
David S. Miller
davem@dm.cobaltmicro.com

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