Re: virt_to_page/pci_map_page vs. pci_map_single

[Jes Sorensen <jes@trained-monkey.org>]

>>>>> "Jamie" == Jamie Wellnitz <Jamie.Wellnitz@emulex.com> writes:

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

Jamie> How is this preferable to:

Jamie> pci_map_single( pci_dev, buffer, len, direction);

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

virt_to_page() can handle any page in the standard kernel region
including pages that are physically in 64-bit space if the
architecture requires it. It doesn't handle vmalloc pages etc. but
one shouldn't try and dynamically map vmalloc pages at
random. pci_map_page() can handle all memory in the system though as
every page that can be mapped has a struct page * entry.

pci_map_page() is the correct API to use, pci_map_single() is
deprecated.

Cheers,
Jes