Re: pci segments/domains

["David S. Miller" <davem@redhat.com>]

   From: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
   Date: Fri, 17 May 2002 15:39:03 +0400
   
   What about
   dma_addr_t pci_to_pci_map_single(struct pci_dev *master,
   				 struct pci_dev *target,
   				 dma_addr_t tgt_addr, size_t size, int dir)
   
   Could be implemented without much pain if there is enough interest. :-)
   
tgt_addr does not make any sense, we are trying to DMA to a device
resource, so pass a "struct resource *" and "unsigned long res_offset"
instead of tgt_addr.

So, as a (real life) example, suppose you wanted to portably point
your BTTV card at the framebuffer of a video card, you'd do
something like:

	res = fb_pdev->resource[1];
	res_off = OFFSET_INTO_FRAMEBUFFER;
	bttv_dma_addr = pci_to_pci_map_single(struct pci_dev *bttv_pdev,
					      struct pci_dev *fb_pdev,
					      res, res_off, size,
					      PCI_DMA_FROMDEVICE);

Note the direction is in terms of the master.  The DMA is coming
"from" the master in this "BTTV capture to framebuffer" case.