question about dynamic dma?

I have a silly doubt about the pci-dma interface .
Is there any relevance of pci-dma interface on a
32 bit plateform? (though i understand its relevance on
64 bit plateform)
also in DMA-MAPPING.txt written that drivers using
this interface , should no more use virt_to_bus and
like stuffs.
what is the special significance of this?
Is it somewhere related to snooping during DMA
(as part of cache consistency protocol) ?
If anyone can explain this briefly , it will be
much helpful.
Regards..

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