virt_to_page/pci_map_page vs. pci_map_single

[Jamie Wellnitz <Jamie.Wellnitz@emulex.com>]

I see code similar to the following in a few drivers (qlogicfc,
sym53c8xx, acenic does something similar):

page = virt_to_page(buffer);
offset = ((unsigned long)buffer & ~PAGE_MASK);
busaddr = pci_map_page(pci_dev, page, offset, len, direction);

How is this preferable to:

pci_map_single( pci_dev, buffer, len, direction);

?

pci_map_single can't handle highmem pages (because they don't have a
kernel virtual address) but doesn't virt_to_page suffer from the same
limitation?  Is there some benefit on architectures that don't have
highmem?

Thanks,
Jamie Wellnitz
Jamie.Wellnitz@emulex.com