Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: A question about ZONE_DMA | Date | Wed, 13 Oct 2010 16:57:17 +0200 |
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On Wednesday 13 October 2010, Casey Dahlin wrote: > So if I understand correctly, ZONE_DMA exists to separate and preserve the > chunk of memory to which older ISA cards are capable of doing DMA. The question > that arises for me is: > > 1) Why do all 32-bit boxes have a ZONE_DMA when surely only a tiny and > shrinking number of them have a need for it? > > 2) Why do any 64-bit boxes have a ZONE_DMA? Is there really some godless > monster out there who put an early ISA bridge and a 64-bit CPU on the same > motherboard?! > > Can someone shed light on what I'm missing?
There are some ISA devices that have become standard components, like floppy drives. A lot of PCs still have connectors for floppies even though they are hardly used these days.
Some architectures define ZONE_DMA in a different way, e.g. as the lower 2 GB because of device restrictions on 64 bit systems.
Arnd
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