Re: virt_to_page/pci_map_page vs. pci_map_single
From: Jamie Wellnitz
Date: Mon Nov 03 2003 - 17:05:12 EST
On Mon, Nov 03, 2003 at 12:48:42PM -0600, James Bottomley wrote:
> Jamie> The Document/DMA-mapping.txt in 2.6.0-test9 says "To map a
> Jamie> single region, you do:" and then shows pci_map_single. Is
> Jamie> DMA-mapping.txt in need of patching?
> Sounds like it needs an update.
> Erm, I don't think so. pci_map_single() covers a different use case
> from pci_map_page().
> The thing pci_map_single() can do that pci_map_page() can't is cope with
> contiguous regions greater than PAGE_SIZE in length (which you get
> either from kmalloc() or __get_free_pages()). This feature is used in
> the SCSI layer for instance.
Does "pci_map_page(virt_to_page(addr))" handle contiguous regions of
multiple pages? It seems like the i386 implementation will (assuming
we're dealing with kmalloc'd memory). Although the semantics of
map_single seem better to me than map_page, if I'm mapping a single
"region" of multiple pages.
> There has been talk of deprecating dma_map_single() in favour of
> dma_map_sg() (i.e. make all transfers use scatter/gather and eliminate
> dma_map_single() in favour of a single sg entry table) but nothing has
> been done about it (at least as far as I know).
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